From 812f934e77700afedbf5e929b282f29a47b2d9c6 Mon Sep 17 00:00:00 2001 From: Samanta Navarro Date: Thu, 18 May 2023 11:56:17 +0000 Subject: [PATCH] process_prefix_flag: Drop privileges Using --prefix in a setuid binary is quite dangerous. An unprivileged user could prepare a custom shadow file in home directory. During a data race the user could exchange directories with links which could lead to exchange of shadow file in system's /etc directory. This could be used for local privilege escalation. Signed-off-by: Samanta Navarro --- libmisc/prefix_flag.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/libmisc/prefix_flag.c b/libmisc/prefix_flag.c index 56243f2e..d7acb9ca 100644 --- a/libmisc/prefix_flag.c +++ b/libmisc/prefix_flag.c @@ -85,6 +85,15 @@ extern const char* process_prefix_flag (const char* short_opt, int argc, char ** if (prefix != NULL) { + /* Drop privileges */ + if ( (setregid (getgid (), getgid ()) != 0) + || (setreuid (getuid (), getuid ()) != 0)) { + fprintf (log_get_logfd(), + _("%s: failed to drop privileges (%s)\n"), + log_get_progname(), strerror (errno)); + exit (EXIT_FAILURE); + } + if ( prefix[0] == '\0' || !strcmp(prefix, "/")) return ""; /* if prefix is "/" then we ignore the flag option */ /* should we prevent symbolic link from being used as a prefix? */