libceph: fix overflow in osdmap_decode()

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 <elder@inktank.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index df47871b8389..d70aaca4a45d 100644
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -667,6 +667,9 @@ struct ceph_osdmap *osdmap_decode(void **p, void *end)
                 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);