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>

diff --git a/ipc/shm.c b/ipc/shm.c
index dda8f1f..9e51bf2 100644 (file)
--- 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));