selftests/net: psock_fanout seg faults in sock_fanout_read_ring()

The while loop in sock_fanout_read_ring() checks mmap region
bounds after access, causing it to segfault. Fix it to check
count before accessing header->tp_status. This problem can be
reproduced consistently when the test in run as follows:

    make -C tools/testing/selftests TARGETS=net run_tests
    or
    make run_tests from tools/testing/selftests
    or
    make run_test from tools/testing/selftests/net

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/tools/testing/selftests/net/psock_fanout.c b/tools/testing/selftests/net/psock_fanout.c
index 57b9c2b7c4ffbfb5950af351f9157e97a075caac..6f6733331d9597918353464a71af1e9d9e04a251 100644 (file)
--- a/tools/testing/selftests/net/psock_fanout.c
+++ b/tools/testing/selftests/net/psock_fanout.c
@@ -128,7 +128,7 @@ static int sock_fanout_read_ring(int fd, void *ring)
        struct tpacket2_hdr *header = ring;
        int count = 0;
 
-       while (header->tp_status & TP_STATUS_USER && count < RING_NUM_FRAMES) {
+       while (count < RING_NUM_FRAMES && header->tp_status & TP_STATUS_USER) {
                count++;
                header = ring + (count * getpagesize());
        }