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tar,unzip: postpone creation of symlinks with "suspicious" targets

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This mostly reverts commit bc9bbeb2b8
"libarchive: do not extract unsafe symlinks unless $EXTRACT_UNSAFE_SYMLINKS=1"

Users report that it is somewhat too restrictive. See
https://bugs.busybox.net/show_bug.cgi?id=8411

In particular, this interferes with unpacking of busybox-based
filesystems with links like "sbin/applet" -> "../bin/busybox".

The change is made smaller by deleting ARCHIVE_EXTRACT_QUIET flag -
it is unused since 2010, and removing conditionals on it
allows commonalizing some error message codes.

function                                             old     new   delta
create_or_remember_symlink                             -      94     +94
create_symlinks_from_list                              -      64     +64
tar_main                                            1002    1006      +4
unzip_main                                          2732    2724      -8
data_extract_all                                     984     891     -93
unsafe_symlink_target                                147       -    -147
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 1/2 up/down: 162/-248)          Total: -86 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2018-02-20 15:57:45 +01:00
parent 95121d98e6
commit a84db18fc7
6 changed files with 71 additions and 82 deletions
Download Patch File Download Diff File Expand all files Collapse all files

65
archival/libarchive/unsafe_symlink_target.c
View File

@@ -5,44 +5,37 @@
#include "libbb.h"
#include "bb_archive.h"
int FAST_FUNC unsafe_symlink_target(const char *target)
void FAST_FUNC create_or_remember_symlink(llist_t **symlink_placeholders,
const char *target,
const char *linkname)
{
const char *dot;
if (target[0] == '/') {
const char *var;
unsafe:
var = getenv("EXTRACT_UNSAFE_SYMLINKS");
if (var) {
if (LONE_CHAR(var, '1'))
return 0; /* pretend it's safe */
return 1; /* "UNSAFE!" */
}
bb_error_msg("skipping unsafe symlink to '%s' in archive,"
" set %s=1 to extract",
target,
"EXTRACT_UNSAFE_SYMLINKS"
if (target[0] == '/' || strstr(target, "..")) {
llist_add_to(symlink_placeholders,
xasprintf("%s%c%s", linkname, '\0', target)
);
/* Prevent further messages */
setenv("EXTRACT_UNSAFE_SYMLINKS", "0", 0);
return 1; /* "UNSAFE!" */
return;
}
dot = target;
for (;;) {
dot = strchr(dot, '.');
if (!dot)
return 0; /* safe target */
/* Is it a path component starting with ".."? */
if ((dot[1] == '.')
&& (dot == target || dot[-1] == '/')
/* Is it exactly ".."? */
&& (dot[2] == '/' || dot[2] == '\0')
) {
goto unsafe;
}
/* NB: it can even be trailing ".", should only add 1 */
dot += 1;
if (symlink(target, linkname) != 0) {
/* shared message */
bb_perror_msg_and_die("can't create %slink '%s' to '%s'",
"sym", linkname, target
);
}
}
void FAST_FUNC create_symlinks_from_list(llist_t *list)
{
while (list) {
char *target;
target = list->data + strlen(list->data) + 1;
if (symlink(target, list->data)) {
/* shared message */
bb_error_msg_and_die("can't create %slink '%s' to '%s'",
"sym",
list->data, target
);
}
list = list->link;
}
}