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authorVasiliy Kulikov <segoon@openwall.com>2011-08-08 19:02:04 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2011-08-11 11:24:42 -0700
commit72fa59970f8698023045ab0713d66f3f4f96945c (patch)
treeed9a5eaf8212270d464c6d4396ae5a568352a997 /kernel/cred.c
parent1d229d54dbc26971142f61c3d271a68db236d178 (diff)
downloadlinux-72fa59970f8698023045ab0713d66f3f4f96945c.tar.gz
move RLIMIT_NPROC check from set_user() to do_execve_common()
The patch http://lkml.org/lkml/2003/7/13/226 introduced an RLIMIT_NPROC check in set_user() to check for NPROC exceeding via setuid() and similar functions. Before the check there was a possibility to greatly exceed the allowed number of processes by an unprivileged user if the program relied on rlimit only. But the check created new security threat: many poorly written programs simply don't check setuid() return code and believe it cannot fail if executed with root privileges. So, the check is removed in this patch because of too often privilege escalations related to buggy programs. The NPROC can still be enforced in the common code flow of daemons spawning user processes. Most of daemons do fork()+setuid()+execve(). The check introduced in execve() (1) enforces the same limit as in setuid() and (2) doesn't create similar security issues. Neil Brown suggested to track what specific process has exceeded the limit by setting PF_NPROC_EXCEEDED process flag. With the change only this process would fail on execve(), and other processes' execve() behaviour is not changed. Solar Designer suggested to re-check whether NPROC limit is still exceeded at the moment of execve(). If the process was sleeping for days between set*uid() and execve(), and the NPROC counter step down under the limit, the defered execve() failure because NPROC limit was exceeded days ago would be unexpected. If the limit is not exceeded anymore, we clear the flag on successful calls to execve() and fork(). The flag is also cleared on successful calls to set_user() as the limit was exceeded for the previous user, not the current one. Similar check was introduced in -ow patches (without the process flag). v3 - clear PF_NPROC_EXCEEDED on successful calls to set_user(). Reviewed-by: James Morris <jmorris@namei.org> Signed-off-by: Vasiliy Kulikov <segoon@openwall.com> Acked-by: NeilBrown <neilb@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/cred.c')
-rw-r--r--kernel/cred.c6
1 files changed, 2 insertions, 4 deletions
diff --git a/kernel/cred.c b/kernel/cred.c
index 174fa84eca3..8ef31f53c44 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -508,10 +508,8 @@ int commit_creds(struct cred *new)
key_fsgid_changed(task);
/* do it
- * - What if a process setreuid()'s and this brings the
- * new uid over his NPROC rlimit? We can check this now
- * cheaply with the new uid cache, so if it matters
- * we should be checking for it. -DaveM
+ * RLIMIT_NPROC limits on user->processes have already been checked
+ * in set_user().
*/
alter_cred_subscribers(new, 2);
if (new->user != old->user)