rbd: fix integer overflow in rbd_header_from_disk()

ondisk->snap_count is read from disk via rbd_req_sync_read() and thus
needs validation.  Otherwise, a bogus `snap_count' could overflow the
kmalloc() size, leading to memory corruption.

Also use `u32' consistently for `snap_count'.

[elder@dreamhost.com: changed to use UINT_MAX rather than ULONG_MAX]

Signed-off-by: Xi Wang <xi.wang@gmail.com>
Reviewed-by: Alex Elder <elder@dreamhost.com>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index ca59d4d..a75fe93 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -487,16 +487,18 @@ static void rbd_coll_release(struct kref *kref)
  */
 static int rbd_header_from_disk(struct rbd_image_header *header,
                                 struct rbd_image_header_ondisk *ondisk,
-                                int allocated_snaps,
+                                u32 allocated_snaps,
                                 gfp_t gfp_flags)
 {
-       int i;
-       u32 snap_count;
+       u32 i, snap_count;
 
        if (memcmp(ondisk, RBD_HEADER_TEXT, sizeof(RBD_HEADER_TEXT)))
                return -ENXIO;
 
        snap_count = le32_to_cpu(ondisk->snap_count);
+       if (snap_count > (UINT_MAX - sizeof(struct ceph_snap_context))
+                        / sizeof (*ondisk))
+               return -EINVAL;
        header->snapc = kmalloc(sizeof(struct ceph_snap_context) +
                                snap_count * sizeof (*ondisk),
                                gfp_flags);
@@ -1591,7 +1593,7 @@ static int rbd_read_header(struct rbd_device *rbd_dev,
 {
        ssize_t rc;
        struct rbd_image_header_ondisk *dh;
-       int snap_count = 0;
+       u32 snap_count = 0;
        u64 ver;
        size_t len;