libceph: fix overflow in __decode_pool_names()

`len' is read from network and thus needs validation.  Otherwise a
large `len' would cause out-of-bounds access via the memcpy() call.
In addition, len = 0xffffffff would overflow the kmalloc() size,
leading to out-of-bounds write.

This patch adds a check of `len' via ceph_decode_need().  Also use
kstrndup rather than kmalloc/memcpy.

[elder@inktank.com: added -ENOMEM return for null kstrndup() result]

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

1 files changed, 7 insertions, 6 deletions

diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index 1892c523c43c..df47871b8389 100644
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -488,15 +488,16 @@ static int __decode_pool_names(void **p, void *end, struct ceph_osdmap *map)
                 ceph_decode_32_safe(p, end, pool, bad);
                 ceph_decode_32_safe(p, end, len, bad);
                 dout("  pool %d len %d\n", pool, len);
+                ceph_decode_need(p, end, len, bad);
                 pi = __lookup_pg_pool(&map->pg_pools, pool);
                 if (pi) {
+                        char *name = kstrndup(*p, len, GFP_NOFS);
+
+                        if (!name)
+                                return -ENOMEM;
                         kfree(pi->name);
-                        pi->name = kmalloc(len + 1, GFP_NOFS);
-                        if (pi->name) {
-                                memcpy(pi->name, *p, len);
-                                pi->name[len] = '\0';
-                                dout("  name is %s\n", pi->name);
-                        }
+                        pi->name = name;
+                        dout("  name is %s\n", pi->name);
                 }
                 *p += len;
         }