[PATCH 4.14 03/77] net: test nouarg before dereferencing zerocopy pointers

Greg Kroah-Hartman
2019-05-23T19:11:03Z

From: Willem de Bruijn <willemb@google.com>

[ Upstream commit 185ce5c38ea76f29b6bd9c7c8c7a5e5408834920 ]

Zerocopy skbs without completion notification were added for packet
sockets with PACKET_TX_RING user buffers. Those signal completion
through the TP_STATUS_USER bit in the ring. Zerocopy annotation was
added only to avoid premature notification after clone or orphan, by
triggering a copy on these paths for these packets.

The mechanism had to define a special "no-uarg" mode because packet
sockets already use skb_uarg(skb) == skb_shinfo(skb)->destructor_arg
for a different pointer.

Before deferencing skb_uarg(skb), verify that it is a real pointer.

Fixes: 5cd8d46ea1562 ("packet: copy user buffers before orphan or clone")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/skbuff.h | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1310,10 +1310,12 @@ static inline void skb_zcopy_clear(struc
struct ubuf_info *uarg = skb_zcopy(skb);

if (uarg) {
- if (uarg->callback == sock_zerocopy_callback) {
+ if (skb_zcopy_is_nouarg(skb)) {
+ /* no notification callback */
+ } else if (uarg->callback == sock_zerocopy_callback) {
uarg->zerocopy = uarg->zerocopy && zerocopy;
sock_zerocopy_put(uarg);
- } else if (!skb_zcopy_is_nouarg(skb)) {
+ } else {
uarg->callback(uarg, zerocopy);
}

@@ -2572,7 +2574,8 @@ static inline int skb_orphan_frags(struc
{
if (likely(!skb_zcopy(skb)))
return 0;
- if (skb_uarg(skb)->callback == sock_zerocopy_callback)
+ if (!skb_zcopy_is_nouarg(skb) &&
+ skb_uarg(skb)->callback == sock_zerocopy_callback)
return 0;
return skb_copy_ubufs(skb, gfp_mask);
}