3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Xi Wang <xi.wang@gmail.com>

(cherry picked from commit e91a9b639a691e0982088b5954eaafb5a25c8f1c)

On 32-bit systems, a large `n' would overflow `n * sizeof(u32)' and bypass
the check ceph_decode_need(p, end, n * sizeof(u32), bad).  It would also
overflow the subsequent kmalloc() size, leading to out-of-bounds write.

Signed-off-by: Xi Wang <xi.wang@gmail.com>
Reviewed-by: Alex Elder <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ceph/osdmap.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c

@@ -674,6 +674,9 @@ struct ceph_osdmap *osdmap_decode(void *
 		ceph_decode_need(p, end, sizeof(u32) + sizeof(u64), bad);
 		ceph_decode_copy(p, &pgid, sizeof(pgid));
 		n = ceph_decode_32(p);
+		err = -EINVAL;
+		if (n > (UINT_MAX - sizeof(*pg)) / sizeof(u32))
+			goto bad;
 		ceph_decode_need(p, end, n * sizeof(u32), bad);
 		err = -ENOMEM;
 		pg = kmalloc(sizeof(*pg) + n*sizeof(u32), GFP_NOFS);