fib_trie: Address possible NULL pointer dereference in resize

If the inflate call failed it would return NULL.  As a result tp would be
set to NULL and cause use to trigger a NULL pointer dereference in
should_halve if the inflate failed on the first attempt.

In order to prevent this we should decrement max_work before we actually
attempt to inflate as this will force us to exit before attempting to halve
a node we should have inflated.  In order to keep things symmetric between
inflate and halve I went ahead and also moved the decrement of max_work for
the halve case as well so we take care of that before we actually attempt
to halve the tnode.

Fixes: 88bae714 ("fib_trie: Add key vector to root, return parent key_vector in resize")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 4 deletions

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 44cab1d41463..83290beaf7cf 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -830,7 +830,7 @@ static struct key_vector *resize(struct trie *t, struct key_vector *tn)
         /* Double as long as the resulting node has a number of
          * nonempty nodes that are above the threshold.
          */
-        while (should_inflate(tp, tn) && max_work) {
+        while (should_inflate(tp, tn) && max_work--) {
                 tp = inflate(t, tn);
                 if (!tp) {
 #ifdef CONFIG_IP_FIB_TRIE_STATS
@@ -839,7 +839,6 @@ static struct key_vector *resize(struct trie *t, struct key_vector *tn)
                         break;
                 }
 
-                max_work--;
                 tn = get_child(tp, cindex);
         }
 
@@ -850,7 +849,7 @@ static struct key_vector *resize(struct trie *t, struct key_vector *tn)
         /* Halve as long as the number of empty children in this
          * node is above threshold.
          */
-        while (should_halve(tp, tn) && max_work) {
+        while (should_halve(tp, tn) && max_work--) {
                 tp = halve(t, tn);
                 if (!tp) {
 #ifdef CONFIG_IP_FIB_TRIE_STATS
@@ -859,7 +858,6 @@ static struct key_vector *resize(struct trie *t, struct key_vector *tn)
                         break;
                 }
 
-                max_work--;
                 tn = get_child(tp, cindex);
         }