rds: fix an integer overflow test in rds_info_getsockopt()

commit 468b732b6f76b138c0926eadf38ac88467dcd271 upstream.

"len" is a signed integer.  We check that len is not negative, so it
goes from zero to INT_MAX.  PAGE_SIZE is unsigned long so the comparison
is type promoted to unsigned long.  ULONG_MAX - 4095 is a higher than
INT_MAX so the condition can never be true.

I don't know if this is harmful but it seems safe to limit "len" to
INT_MAX - 4095.

Fixes: a8c879a7ee98 ('RDS: Info and stats')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/rds/info.c b/net/rds/info.c
index f1c016c..a4adb39 100644 (file)
--- a/net/rds/info.c
+++ b/net/rds/info.c
@@ -176,7 +176,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
 
        /* check for all kinds of wrapping and the like */
        start = (unsigned long)optval;
-       if (len < 0 || len + PAGE_SIZE - 1 < len || start + len < start) {
+       if (len < 0 || len > INT_MAX - PAGE_SIZE + 1 || start + len < start) {
                ret = -EINVAL;
                goto out;
        }