ipc/shm.c: check for overflows of shm_tot

shm_tot counts the total number of pages used by shm segments.

If SHMALL is ULONG_MAX (or nearly ULONG_MAX), then the number can
overflow.  Subsequent calls to shmctl(,SHM_INFO,) would return wrong
values for shm_tot.

The patch adds a detection for overflows.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Acked-by: Davidlohr Bueso <davidlohr@hp.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index dda8f1ff3c35..9e51bf246344 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -493,7 +493,8 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
         if (size < SHMMIN || size > ns->shm_ctlmax)
                 return -EINVAL;
 
-        if (ns->shm_tot + numpages > ns->shm_ctlall)
+        if (ns->shm_tot + numpages < ns->shm_tot ||
+                        ns->shm_tot + numpages > ns->shm_ctlall)
                 return -ENOSPC;
 
         shp = ipc_rcu_alloc(sizeof(*shp));