SHMMAX is the upper limit of a shared memory segment,
counted in bytes. The actual allocation is that size, rounded
up to the next full page.
Add a check that prevents the creation of segments where the
rounded up size causes an integer overflow.

Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
---
 ipc/shm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/ipc/shm.c b/ipc/shm.c
index 2dfa3d6..f000696 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -493,6 +493,9 @@ static int newseg(struct ipc_namespace *ns, struct 
ipc_params *params)
        if (size < SHMMIN || size > ns->shm_ctlmax)
                return -EINVAL;
 
+       if (numpages << PAGE_SHIFT < size)
+               return -ENOSPC;
+
        if (ns->shm_tot + numpages < ns->shm_tot ||
                        ns->shm_tot + numpages > ns->shm_ctlall)
                return -ENOSPC;
-- 
1.9.0

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