[PATCH] quic: Avoid possible buffer overflow in find_bucket

Proved by fuzzing the code.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Acked-by: Uri Lublin <uril@redhat.com>
Gbp-Pq: Name CVE-2020-14355_part4.patch

diff --git a/spice-common/common/quic_family_tmpl.c b/spice-common/common/quic_family_tmpl.c
index 9a434e038b11402f833c3578dbf846aae35c265d..4038dbaacdcebd7f9ffa99f406de219c34145318 100644 (file)
--- a/spice-common/common/quic_family_tmpl.c
+++ b/spice-common/common/quic_family_tmpl.c
@@ -107,7 +107,12 @@ static s_bucket *FNAME(find_bucket)(Channel *channel, const unsigned int val)
 {
     spice_assert(val < (0x1U << BPC));
 
-    return channel->_buckets_ptrs[val];
+    /* The and (&) here is to avoid buffer overflows in case of garbage or malicious
+     * attempts. Is much faster then using comparisons and save us from such situations.
+     * Note that on normal build the check above won't be compiled as this code path
+     * is pretty hot and would cause speed regressions.
+     */
+    return channel->_buckets_ptrs[val & ((1U << BPC) - 1)];
 }
 
 #undef FNAME