From f4293f9fbc2b855878f549d9124bdd638fb08c60 Mon Sep 17 00:00:00 2001 From: Skyler Ferrante Date: Fri, 8 Mar 2024 12:53:21 -0500 Subject: [PATCH] lib/, src/: Add checks for fd omission Adding function check_fds to new file fd.c. The function check_fds should be called in every setuid/setgid program. Co-developed-by: Alejandro Colomar Cherry-picked-from: d2f2c1877a30 ("Adding checks for fd omission") Link: Link: [alx: It seems we shouldn't need this, as libc does it for us. But it ] [ shouldn't hurt either. Let's be paranoic. ] Cc: Cc: "Serge E. Hallyn" Cc: "Skyler Ferrante (RIT Student)" Cc: Iker Pedrosa Cc: Christian Brauner Cc: Rich Felker Cc: Andreas Schwab Cc: Thorsten Glaser Cc: NRK Cc: Florian Weimer Cc: enh Cc: Laurent Bercot Cc: Gabriel Ravier Cc: Zack Weinberg Signed-off-by: Alejandro Colomar --- lib/Makefile.am | 1 + lib/fd.c | 41 +++++++++++++++++++++++++++++++++++++++++ lib/prototypes.h | 3 +++ src/chage.c | 7 +++---- src/chfn.c | 4 +++- src/chsh.c | 1 + src/expiry.c | 5 +++-- src/gpasswd.c | 2 ++ src/newgrp.c | 3 +++ src/passwd.c | 1 + src/su.c | 2 ++ 11 files changed, 63 insertions(+), 7 deletions(-) create mode 100644 lib/fd.c diff --git a/lib/Makefile.am b/lib/Makefile.am index 7db960c8..1146e39b 100644 --- a/lib/Makefile.am +++ b/lib/Makefile.am @@ -53,6 +53,7 @@ libshadow_la_SOURCES = \ faillog.h \ failure.c \ failure.h \ + fd.c \ fields.c \ find_new_gid.c \ find_new_uid.c \ diff --git a/lib/fd.c b/lib/fd.c new file mode 100644 index 00000000..bcfa374a --- /dev/null +++ b/lib/fd.c @@ -0,0 +1,41 @@ +// SPDX-FileCopyrightText: 2024, Skyler Ferrante +// SPDX-License-Identifier: BSD-3-Clause + +/** + * To protect against file descriptor omission attacks, we open the std file + * descriptors with /dev/null if they are not already open. Code is based on + * fix_fds from sudo.c. + */ + +#include +#include +#include + +#include "prototypes.h" + +static void check_fd(int fd); + +void +check_fds(void) +{ + /** + * Make sure stdin, stdout, stderr are open + * If they are closed, set them to /dev/null + */ + check_fd(STDIN_FILENO); + check_fd(STDOUT_FILENO); + check_fd(STDERR_FILENO); +} + +static void +check_fd(int fd) +{ + int devnull; + + if (fcntl(fd, F_GETFL, 0) != -1) + return; + + devnull = open("/dev/null", O_RDWR); + if (devnull != fd) + abort(); +} diff --git a/lib/prototypes.h b/lib/prototypes.h index cacf3d21..b9d4fbdf 100644 --- a/lib/prototypes.h +++ b/lib/prototypes.h @@ -127,6 +127,9 @@ extern void initenv (void); extern void set_env (int, char *const *); extern void sanitize_env (void); +/* fd.c */ +extern void check_fds (void); + /* fields.c */ extern void change_field (char *, size_t, const char *); extern int valid_field (const char *, const char *); diff --git a/src/chage.c b/src/chage.c index b64961f6..18ad80eb 100644 --- a/src/chage.c +++ b/src/chage.c @@ -762,13 +762,12 @@ int main (int argc, char **argv) gid_t rgid; const struct passwd *pw; - /* - * Get the program name so that error messages can use it. - */ + sanitize_env (); + check_fds (); + log_set_progname(Prog); log_set_logfd(stderr); - sanitize_env (); (void) setlocale (LC_ALL, ""); (void) bindtextdomain (PACKAGE, LOCALEDIR); (void) textdomain (PACKAGE); diff --git a/src/chfn.c b/src/chfn.c index 2fd81d3d..213b0bb7 100644 --- a/src/chfn.c +++ b/src/chfn.c @@ -616,10 +616,12 @@ int main (int argc, char **argv) char new_gecos[BUFSIZ]; /* buffer for new GECOS fields */ char *user; + sanitize_env (); + check_fds (); + log_set_progname(Prog); log_set_logfd(stderr); - sanitize_env (); (void) setlocale (LC_ALL, ""); (void) bindtextdomain (PACKAGE, LOCALEDIR); (void) textdomain (PACKAGE); diff --git a/src/chsh.c b/src/chsh.c index e29ac580..c019e357 100644 --- a/src/chsh.c +++ b/src/chsh.c @@ -473,6 +473,7 @@ int main (int argc, char **argv) const struct passwd *pw; /* Password entry from /etc/passwd */ sanitize_env (); + check_fds (); log_set_progname(Prog); log_set_logfd(stderr); diff --git a/src/expiry.c b/src/expiry.c index 673cbc3c..1900335e 100644 --- a/src/expiry.c +++ b/src/expiry.c @@ -123,11 +123,12 @@ int main (int argc, char **argv) struct passwd *pwd; struct spwd *spwd; + sanitize_env (); + check_fds (); + log_set_progname(Prog); log_set_logfd(stderr); - sanitize_env (); - /* * Start by disabling all of the keyboard signals. */ diff --git a/src/gpasswd.c b/src/gpasswd.c index 34205cc7..a3fa80d0 100644 --- a/src/gpasswd.c +++ b/src/gpasswd.c @@ -956,6 +956,8 @@ int main (int argc, char **argv) #endif sanitize_env (); + check_fds (); + (void) setlocale (LC_ALL, ""); (void) bindtextdomain (PACKAGE, LOCALEDIR); (void) textdomain (PACKAGE); diff --git a/src/newgrp.c b/src/newgrp.c index 68e80fe9..051b5675 100644 --- a/src/newgrp.c +++ b/src/newgrp.c @@ -390,6 +390,9 @@ int main (int argc, char **argv) #ifdef WITH_AUDIT audit_help_open (); #endif + + check_fds (); + (void) setlocale (LC_ALL, ""); (void) bindtextdomain (PACKAGE, LOCALEDIR); (void) textdomain (PACKAGE); diff --git a/src/passwd.c b/src/passwd.c index 3ef0cf3f..b9873b06 100644 --- a/src/passwd.c +++ b/src/passwd.c @@ -730,6 +730,7 @@ int main (int argc, char **argv) const struct spwd *sp; /* Shadow file entry for user */ sanitize_env (); + check_fds (); log_set_progname(Prog); log_set_logfd(stderr); diff --git a/src/su.c b/src/su.c index 8c3be346..f9a18e25 100644 --- a/src/su.c +++ b/src/su.c @@ -999,6 +999,8 @@ int main (int argc, char **argv) int ret; #endif /* USE_PAM */ + check_fds (); + (void) setlocale (LC_ALL, ""); (void) bindtextdomain (PACKAGE, LOCALEDIR); (void) textdomain (PACKAGE);