ppp: deflate: never return len larger than output buffer

commit e2a4800e75780ccf4e6c2487f82b688ba736eb18 upstream.

When we've run out of space in the output buffer to store more data, we
will call zlib_deflate with a NULL output buffer until we've consumed
remaining input.

When this happens, olen contains the size the output buffer would have
consumed iff we'd have had enough room.

This can later cause skb_over_panic when ppp_generic skb_put()s
the returned length.

Reported-by: Iain Douglas <centos@1n6.org.uk>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/drivers/net/ppp/ppp_deflate.c b/drivers/net/ppp/ppp_deflate.c
index 602c625d95d5e26ba0c79f9ae6af2dd92f1f3c93..b5edc7f96a392d0080400ed4285cfb84e86d9e5c 100644 (file)
--- a/drivers/net/ppp/ppp_deflate.c
+++ b/drivers/net/ppp/ppp_deflate.c
@@ -246,7 +246,7 @@ static int z_compress(void *arg, unsigned char *rptr, unsigned char *obuf,
        /*
         * See if we managed to reduce the size of the packet.
         */
-       if (olen < isize) {
+       if (olen < isize && olen <= osize) {
                state->stats.comp_bytes += olen;
                state->stats.comp_packets++;
        } else {