tar: postpone creation of symlinks with "suspicious" targets. Closes 8411
function old new delta data_extract_all 968 1038 +70 tar_main 952 986 +34 scan_tree 258 262 +4 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 3/0 up/down: 108/0) Total: 108 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
parent
c810978552
commit
b920a38dc0
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@ -128,10 +128,11 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
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res = link(hard_link, dst_name);
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if (res != 0 && !(archive_handle->ah_flags & ARCHIVE_EXTRACT_QUIET)) {
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/* shared message */
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bb_perror_msg("can't create %slink "
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"%s to %s", "hard",
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bb_perror_msg("can't create %slink '%s' to '%s'",
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"hard",
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dst_name,
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hard_link);
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hard_link
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);
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}
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/* Hardlinks have no separate mode/ownership, skip chown/chmod */
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goto ret;
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@ -178,15 +179,44 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
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case S_IFLNK:
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/* Symlink */
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//TODO: what if file_header->link_target == NULL (say, corrupted tarball?)
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/* To avoid a directory traversal attack via symlinks,
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* for certain link targets postpone creation of symlinks.
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*
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* For example, consider a .tar created via:
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* $ tar cvf bug.tar anything.txt
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* $ ln -s /tmp symlink
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* $ tar --append -f bug.tar symlink
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* $ rm symlink
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* $ mkdir symlink
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* $ tar --append -f bug.tar symlink/evil.py
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*
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* This will result in an archive that contains:
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* $ tar --list -f bug.tar
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* anything.txt
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* symlink [-> /tmp]
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* symlink/evil.py
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*
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* Untarring bug.tar would otherwise place evil.py in '/tmp'.
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*/
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if (file_header->link_target[0] == '/'
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|| strstr(file_header->link_target, "..")
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) {
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llist_add_to(&archive_handle->symlink_placeholders,
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xasprintf("%s%c%s", file_header->name, '\0', file_header->link_target)
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);
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break;
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}
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res = symlink(file_header->link_target, dst_name);
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if (res != 0
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&& !(archive_handle->ah_flags & ARCHIVE_EXTRACT_QUIET)
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) {
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/* shared message */
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bb_perror_msg("can't create %slink "
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"%s to %s", "sym",
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bb_perror_msg("can't create %slink '%s' to '%s'",
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"sym",
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dst_name,
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file_header->link_target);
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file_header->link_target
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);
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}
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break;
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case S_IFSOCK:
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@ -22,24 +22,6 @@
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*
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* Licensed under GPLv2 or later, see file LICENSE in this source tree.
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*/
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/* TODO: security with -C DESTDIR option can be enhanced.
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* Consider tar file created via:
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* $ tar cvf bug.tar anything.txt
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* $ ln -s /tmp symlink
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* $ tar --append -f bug.tar symlink
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* $ rm symlink
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* $ mkdir symlink
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* $ tar --append -f bug.tar symlink/evil.py
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*
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* This will result in an archive which contains:
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* $ tar --list -f bug.tar
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* anything.txt
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* symlink
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* symlink/evil.py
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*
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* Untarring it puts evil.py in '/tmp' even if the -C DESTDIR is given.
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* This doesn't feel right, and IIRC GNU tar doesn't do that.
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*/
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//config:config TAR
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//config: bool "tar (40 kb)"
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@ -296,6 +278,23 @@ static void chksum_and_xwrite(int fd, struct tar_header_t* hp)
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xwrite(fd, hp, sizeof(*hp));
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}
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static void replace_symlink_placeholders(llist_t *list)
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{
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while (list) {
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char *target;
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target = list->data + strlen(list->data) + 1;
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if (symlink(target, list->data)) {
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/* shared message */
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bb_error_msg_and_die("can't create %slink '%s' to '%s'",
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"sym",
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list->data, target
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);
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}
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list = list->link;
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}
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}
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#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
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static void writeLongname(int fd, int type, const char *name, int dir)
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{
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@ -1252,6 +1251,8 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
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while (get_header_tar(tar_handle) == EXIT_SUCCESS)
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bb_got_signal = EXIT_SUCCESS; /* saw at least one header, good */
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replace_symlink_placeholders(tar_handle->symlink_placeholders);
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/* Check that every file that should have been extracted was */
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while (tar_handle->accept) {
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if (!find_list_entry(tar_handle->reject, tar_handle->accept->data)
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16
archival/tar_symlink_attack
Executable file
16
archival/tar_symlink_attack
Executable file
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@ -0,0 +1,16 @@
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#!/bin/sh
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# Makes "symlink attack" tarball (needs GNU tar for --append)
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true >anything.txt
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tar cvf tar_symlink_attack.tar anything.txt
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rm anything.txt
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ln -s /tmp symlink
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tar --append -f tar_symlink_attack.tar symlink
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rm symlink
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mkdir symlink
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echo BUG >symlink/bb_test_evilfile
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tar --append -f tar_symlink_attack.tar symlink/bb_test_evilfile
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rm symlink/bb_test_evilfile
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rmdir symlink
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@ -33,7 +33,7 @@ int link_main(int argc UNUSED_PARAM, char **argv)
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if (link(argv[0], argv[1]) != 0) {
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/* shared message */
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bb_perror_msg_and_die("can't create %slink "
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"%s to %s", "hard",
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"'%s' to '%s'", "hard",
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argv[1], argv[0]
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);
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}
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@ -64,6 +64,9 @@ typedef struct archive_handle_t {
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/* Currently processed file's header */
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file_header_t *file_header;
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/* List of symlink placeholders */
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llist_t *symlink_placeholders;
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/* Process the header component, e.g. tar -t */
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void FAST_FUNC (*action_header)(const file_header_t *);
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@ -188,6 +191,7 @@ char get_header_ar(archive_handle_t *archive_handle) FAST_FUNC;
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char get_header_cpio(archive_handle_t *archive_handle) FAST_FUNC;
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char get_header_tar(archive_handle_t *archive_handle) FAST_FUNC;
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char get_header_tar_gz(archive_handle_t *archive_handle) FAST_FUNC;
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char get_header_tar_xz(archive_handle_t *archive_handle) FAST_FUNC;
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char get_header_tar_bz2(archive_handle_t *archive_handle) FAST_FUNC;
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char get_header_tar_lzma(archive_handle_t *archive_handle) FAST_FUNC;
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char get_header_tar_xz(archive_handle_t *archive_handle) FAST_FUNC;
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@ -10,9 +10,6 @@ unset LC_COLLATE
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unset LC_ALL
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umask 022
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rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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# testing "test name" "script" "expected result" "file input" "stdin"
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testing "Empty file is not a tarball" '\
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@ -53,6 +50,7 @@ dd if=/dev/zero bs=512 count=20 2>/dev/null | tar xvf - 2>&1; echo $?
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"" ""
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SKIP=
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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# "tar cf test.tar input input_dir/ input_hard1 input_hard2 input_hard1 input_dir/ input":
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# GNU tar 1.26 records as hardlinks:
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# input_hard2 -> input_hard1
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@ -64,7 +62,6 @@ SKIP=
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# We also don't use "hrw-r--r--" notation for hardlinks in "tar tv" listing.
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optional FEATURE_TAR_CREATE FEATURE_LS_SORTFILES
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testing "tar hardlinks and repeated files" '\
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rm -rf input_* test.tar 2>/dev/null
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>input_hard1
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ln input_hard1 input_hard2
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mkdir input_dir
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@ -95,10 +92,11 @@ drwxr-xr-x input_dir
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" \
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"" ""
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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optional FEATURE_TAR_CREATE FEATURE_LS_SORTFILES
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testing "tar hardlinks mode" '\
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rm -rf input_* test.tar 2>/dev/null
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>input_hard1
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chmod 741 input_hard1
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ln input_hard1 input_hard2
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@ -128,10 +126,11 @@ Ok: 0
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" \
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"" ""
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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optional FEATURE_TAR_CREATE FEATURE_LS_SORTFILES
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testing "tar symlinks mode" '\
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rm -rf input_* test.tar 2>/dev/null
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>input_file
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chmod 741 input_file
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ln -s input_file input_soft
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@ -159,10 +158,11 @@ lrwxrwxrwx input_file
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" \
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"" ""
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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optional FEATURE_TAR_CREATE FEATURE_TAR_LONG_OPTIONS
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testing "tar --overwrite" "\
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rm -rf input_* test.tar 2>/dev/null
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ln input input_hard
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tar cf test.tar input_hard
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echo WRONG >input
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@ -174,12 +174,13 @@ Ok
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" \
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"Ok\n" ""
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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test x"$SKIP_KNOWN_BUGS" = x"" && {
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# Needs to be run under non-root for meaningful test
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optional FEATURE_TAR_CREATE
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testing "tar writing into read-only dir" '\
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rm -rf input_* test.tar 2>/dev/null
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mkdir input_dir
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>input_dir/input_file
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chmod 550 input_dir
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@ -201,7 +202,9 @@ dr-xr-x--- input_dir
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"" ""
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SKIP=
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}
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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# Had a bug where on extract autodetect first "switched off" -z
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# and then failed to recognize .tgz extension
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optional FEATURE_TAR_CREATE FEATURE_SEAMLESS_GZ GUNZIP
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@ -217,7 +220,9 @@ Ok
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" \
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"" ""
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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# Do we detect XZ-compressed data (even w/o .tar.xz or txz extension)?
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# (the uuencoded hello_world.txz contains one empty file named "hello_world")
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optional UUDECODE FEATURE_TAR_AUTODETECT FEATURE_SEAMLESS_XZ
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@ -236,7 +241,9 @@ AAAEWVo=
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====
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"
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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# On extract, everything up to and including last ".." component is stripped
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optional FEATURE_TAR_CREATE
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testing "tar strips /../ on extract" "\
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@ -255,7 +262,9 @@ Ok
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" \
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"" ""
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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# attack.tar.bz2 has symlink pointing to a system file
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# followed by a regular file with the same name
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# containing "root::0:0::/root:/bin/sh":
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@ -270,6 +279,7 @@ optional UUDECODE FEATURE_TAR_AUTODETECT FEATURE_SEAMLESS_BZ2
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testing "tar does not extract into symlinks" "\
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>>/tmp/passwd && uudecode -o input && tar xf input 2>&1 && rm passwd; cat /tmp/passwd; echo \$?
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" "\
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tar: can't create symlink 'passwd' to '/tmp/passwd'
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0
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" \
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"" "\
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@ -281,12 +291,15 @@ l4/V8LDoe90yiWJhOJvIypgEfxdyRThQkBVn/bI=
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====
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"
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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# And same with -k
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optional UUDECODE FEATURE_TAR_AUTODETECT FEATURE_SEAMLESS_BZ2
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testing "tar -k does not extract into symlinks" "\
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>>/tmp/passwd && uudecode -o input && tar xf input -k 2>&1 && rm passwd; cat /tmp/passwd; echo \$?
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" "\
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tar: can't open 'passwd': File exists
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tar: can't create symlink 'passwd' to '/tmp/passwd'
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0
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" \
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"" "\
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@ -298,7 +311,9 @@ l4/V8LDoe90yiWJhOJvIypgEfxdyRThQkBVn/bI=
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====
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"
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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optional UNICODE_SUPPORT FEATURE_TAR_GNU_EXTENSIONS FEATURE_SEAMLESS_BZ2 FEATURE_TAR_AUTODETECT
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testing "Pax-encoded UTF8 names and symlinks" '\
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tar xvf ../tar.utf8.tar.bz2 2>&1; echo $?
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@ -318,8 +333,36 @@ etc/ssl/certs/f80cc7f6.0 -> EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.pem
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" \
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"" ""
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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cd .. && rm -rf tar.tempdir || exit 1
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mkdir tar.tempdir && cd tar.tempdir || exit 1
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optional FEATURE_SEAMLESS_BZ2 FEATURE_TAR_AUTODETECT
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testing "Symlink attack: create symlink and then write through it" '\
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exec 2>&1
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uudecode -o input && tar xvf input; echo $?
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ls /tmp/bb_test_evilfile
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ls bb_test_evilfile
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ls symlink/bb_test_evilfile
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' "\
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anything.txt
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symlink
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symlink/bb_test_evilfile
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tar: can't create symlink 'symlink' to '/tmp'
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1
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ls: /tmp/bb_test_evilfile: No such file or directory
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ls: bb_test_evilfile: No such file or directory
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symlink/bb_test_evilfile
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" \
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"" "\
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begin-base64 644 tar_symlink_attack.tar.bz2
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QlpoOTFBWSZTWZgs7bQAALT/hMmQAFBAAf+AEMAGJPPv32AAAIAIMAC5thlR
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omAjAmCMADQT1BqNE0AEwAAjAEwElTKeo9NTR6h6gaeoA0DQNLVdwZZ5iNTk
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AQwCAV6S00QFJYhrlfFkVCEDEGtgNVqYrI0uK3ggnt30gqk4e1TTQm5QIAKa
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SJqzRGSFLMmOloHSAcvLiFxxRiQtQZF+qPxbo173ZDISOAoNoPN4PQPhBhKS
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n8fYaKlioCTzL2oXYczyUUIP4u5IpwoSEwWdtoA=
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====
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"
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SKIP=
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cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
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exit $FAILCOUNT
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