rib: fix max depth IPv6 lookup

ASAN found a stack buffer overflow in lib/rib/rte_rib6.c:get_dir.
The fix for the stack buffer overflow was to make sure depth
was always < 128, since when depth = 128 it caused the index
into the ip address to be 16, which read off the end of the array.

While trying to solve the buffer overflow, I noticed that a few
changes could be made to remove the for loop entirely.

Fixes: f7e861e21c46 ("rib: support IPv6")
Cc: stable@dpdk.org
Signed-off-by: Owen Hilyard <ohilyard@iol.unh.edu>
Acked-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>

diff --git a/lib/rib/rte_rib6.c b/lib/rib/rte_rib6.c
index f6c55ee..96424e9 100644 (file)
--- a/lib/rib/rte_rib6.c
+++ b/lib/rib/rte_rib6.c
@@ -79,20 +79,33 @@ is_covered(const uint8_t ip1[RTE_RIB6_IPV6_ADDR_SIZE],
 static inline int
 get_dir(const uint8_t ip[RTE_RIB6_IPV6_ADDR_SIZE], uint8_t depth)
 {
-       int i = 0;
-       uint8_t p_depth, msk;
-
-       for (p_depth = depth; p_depth >= 8; p_depth -= 8)
-               i++;
-
-       msk = 1 << (7 - p_depth);
-       return (ip[i] & msk) != 0;
+       uint8_t index, msk;
+
+       /*
+        * depth & 127 clamps depth to values that will not
+        * read off the end of ip.
+        * depth is the number of bits deep into ip to traverse, and
+        * is incremented in blocks of 8 (1 byte). This means the last
+        * 3 bits are irrelevant to what the index of ip should be.
+        */
+       index = (depth & (UINT8_MAX - 1)) / CHAR_BIT;
+
+       /*
+        * msk is the bitmask used to extract the bit used to decide the
+        * direction of the next step of the binary search.
+        */
+       msk = 1 << (7 - (depth & 7));
+
+       return (ip[index] & msk) != 0;
 }
 
 static inline struct rte_rib6_node *
 get_nxt_node(struct rte_rib6_node *node,
        const uint8_t ip[RTE_RIB6_IPV6_ADDR_SIZE])
 {
+       if (node->depth == RIB6_MAXDEPTH)
+               return NULL;
+
        return (get_dir(ip, node->depth)) ? node->right : node->left;
 }