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process_prefix_flag: Drop privileges

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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 <ferivoz@riseup.net>
This commit is contained in:
Samanta Navarro 2023-05-18 11:56:17 +00:00 committed by Iker Pedrosa
parent 1132b89236
commit 812f934e77
1 changed files with 9 additions and 0 deletions
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9
libmisc/prefix_flag.c
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@ -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? */