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wall,crontab: use xopen_as_uid_gid()

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This fixes a narrow security race in crontab.

function                                             old     new   delta
xopen_as_uid_gid                                       -      80     +80
seteuid                                                -      64     +64
setegid                                                -      64     +64
setreuid                                               -      37     +37
xseteuid                                               -      22     +22
xsetegid                                               -      22     +22
crontab_main                                         590     577     -13
setfsuid                                              33       -     -33
setfsgid                                              33       -     -33
wall_main                                            138     102     -36
open_as_user                                         109       -    -109

   text    data     bss     dec     hex filename
 893539     497    7568  901604   dc1e4 busybox_old
 893618     497    7568  901683   dc233 busybox_unstripped

Signed-off-by: Ryan Mallon <rmallon@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Ryan Mallon 2013-10-08 14:53:29 +02:00 committed by Denys Vlasenko
parent 5906a5c26c
commit 1d30b3f1f6
2 changed files with 2 additions and 31 deletions
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27
miscutils/crontab.c
View File

@ -55,28 +55,6 @@ static void edit_file(const struct passwd *pas, const char *file)
bb_perror_msg_and_die("can't execute '%s'", ptr);
}
static int open_as_user(const struct passwd *pas, const char *file)
{
pid_t pid;
char c;
pid = xvfork();
if (pid) { /* PARENT */
if (wait4pid(pid) == 0) {
/* exitcode 0: child says it can read */
return open(file, O_RDONLY);
}
return -1;
}
/* CHILD */
/* initgroups, setgid, setuid */
change_identity(pas);
/* We just try to read one byte. If it works, file is readable
* under this user. We signal that by exiting with 0. */
_exit(safe_read(xopen(file, O_RDONLY), &c, 1) < 0);
}
int crontab_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int crontab_main(int argc UNUSED_PARAM, char **argv)
{
@ -137,10 +115,7 @@ int crontab_main(int argc UNUSED_PARAM, char **argv)
if (!argv[0])
bb_show_usage();
if (NOT_LONE_DASH(argv[0])) {
src_fd = open_as_user(pas, argv[0]);
if (src_fd < 0)
bb_error_msg_and_die("user %s cannot read %s",
pas->pw_name, argv[0]);
src_fd = xopen_as_uid_gid(argv[0], O_RDONLY, pas->pw_uid, pas->pw_gid);
}
}

6
miscutils/wall.c
View File

@ -41,11 +41,7 @@ int wall_main(int argc UNUSED_PARAM, char **argv)
/* The applet is setuid.
* Access to the file must be under user's uid/gid.
*/
setfsuid(getuid());
setfsgid(getgid());
fd = xopen(argv[1], O_RDONLY);
setfsuid(geteuid());
setfsgid(getegid());
fd = xopen_as_uid_gid(argv[1], O_RDONLY, getuid(), getgid());
}
msg = xmalloc_read(fd, NULL);
if (ENABLE_FEATURE_CLEAN_UP && argv[1])