[PATCH 2/4] ipc/shm.c: check for overflows of shm_tot

[Manfred Spraul]

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@xxxxxxxxxxxxxxxx>
---
 ipc/shm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ipc/shm.c b/ipc/shm.c
index 382e2fb..2dfa3d6 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));
-- 
1.9.0

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