The patch titled
Subject: exec: avoid RLIMIT_STACK races with prlimit()
has been added to the -mm tree. Its filename is
exec-avoid-rlimit_stack-races-with-prlimit.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/exec-avoid-rlimit_stack-races-with-prlimit.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/exec-avoid-rlimit_stack-races-with-prlimit.patch
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------------------------------------------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: exec: avoid RLIMIT_STACK races with prlimit()
While the defense-in-depth RLIMIT_STACK limit on setuid processes was
protected against races from other threads calling setrlimit(), I missed
protecting it against races from external processes calling prlimit().
This adds locking around the change and makes sure that rlim_max is set
too.
Link: http://lkml.kernel.org/r/20171127193457.GA11348@beast
Fixes: 64701dee4178e ("exec: Use sane stack rlimit under secureexec")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reported-by: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>
Reported-by: Brad Spengler <spender@xxxxxxxxxxxxxx>
Cc: James Morris <james.l.morris@xxxxxxxxxx>
Cc: Serge Hallyn <serge@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff -puN fs/exec.c~exec-avoid-rlimit_stack-races-with-prlimit fs/exec.c
--- a/fs/exec.c~exec-avoid-rlimit_stack-races-with-prlimit
+++ a/fs/exec.c
@@ -1340,10 +1340,15 @@ void setup_new_exec(struct linux_binprm
* avoid bad behavior from the prior rlimits. This has to
* happen before arch_pick_mmap_layout(), which examines
* RLIMIT_STACK, but after the point of no return to avoid
- * needing to clean up the change on failure.
+ * races from other threads changing the limits. This also
+ * must be protected from races with prlimit() calls.
*/
+ task_lock(current->group_leader);
if (current->signal->rlim[RLIMIT_STACK].rlim_cur > _STK_LIM)
current->signal->rlim[RLIMIT_STACK].rlim_cur = _STK_LIM;
+ if (current->signal->rlim[RLIMIT_STACK].rlim_max > _STK_LIM)
+ current->signal->rlim[RLIMIT_STACK].rlim_max = _STK_LIM;
+ task_unlock(current->group_leader);
}
arch_pick_mmap_layout(current->mm);
_
Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are
exec-avoid-rlimit_stack-races-with-prlimit.patch
makefile-move-stack-protector-compiler-breakage-test-earlier.patch
makefile-move-stack-protector-availability-out-of-kconfig.patch
makefile-introduce-config_cc_stackprotector_auto.patch