diff mbox

[3.16.y-ckt,127/128] udp: properly support MSG_PEEK with truncated buffers

Message ID 1453672883-2708-128-git-send-email-luis.henriques@canonical.com
State New
Headers show

Commit Message

Luis Henriques Jan. 24, 2016, 10:01 p.m. UTC 
3.16.7-ckt23 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Eric Dumazet <edumazet@google.com>

commit 197c949e7798fbf28cfadc69d9ca0c2abbf93191 upstream.

Backport of this upstream commit into stable kernels :
89c22d8c3b27 ("net: Fix skb csum races when peeking")
exposed a bug in udp stack vs MSG_PEEK support, when user provides
a buffer smaller than skb payload.

In this case,
skb_copy_and_csum_datagram_iovec(skb, sizeof(struct udphdr),
                                 msg->msg_iov);
returns -EFAULT.

This bug does not happen in upstream kernels since Al Viro did a great
job to replace this into :
skb_copy_and_csum_datagram_msg(skb, sizeof(struct udphdr), msg);
This variant is safe vs short buffers.

For the time being, instead reverting Herbert Xu patch and add back
skb->ip_summed invalid changes, simply store the result of
udp_lib_checksum_complete() so that we avoid computing the checksum a
second time, and avoid the problematic
skb_copy_and_csum_datagram_iovec() call.

This patch can be applied on recent kernels as it avoids a double
checksumming, then backported to stable kernels as a bug fix.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 net/ipv4/udp.c | 6 ++++--
 net/ipv6/udp.c | 6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

Comments

Ben Hutchings Jan. 25, 2016, 1:41 a.m. UTC | #1 
On Sun, 2016-01-24 at 22:01 +0000, Luis Henriques wrote:
> 3.16.7-ckt23 -stable review patch.  If anyone has any objections, please let me know.
> 
> ---8<------------------------------------------------------------
> 
> From: Eric Dumazet <edumazet@google.com>
> 
> commit 197c949e7798fbf28cfadc69d9ca0c2abbf93191 upstream.
[...]

Please also revert commit fa89ae5548ed282f0ceb4660b3b93e4e2ee875f3
which was the previous attempt to fix this.

Ben.
Luis Henriques Jan. 25, 2016, 10:54 a.m. UTC | #2 
On Mon, Jan 25, 2016 at 01:41:23AM +0000, Ben Hutchings wrote:
> On Sun, 2016-01-24 at 22:01 +0000, Luis Henriques wrote:
> > 3.16.7-ckt23 -stable review patch.  If anyone has any objections, please let me know.
> > 
> > ---8<------------------------------------------------------------
> > 
> > From: Eric Dumazet <edumazet@google.com>
> > 
> > commit 197c949e7798fbf28cfadc69d9ca0c2abbf93191 upstream.
> [...]
> 
> Please also revert commit fa89ae5548ed282f0ceb4660b3b93e4e2ee875f3
> which was the previous attempt to fix this.
> 

Thanks, I'll add that revert to 3.16.7-ckt23 as well.

Cheers,
--
Luís

> Ben.
> 
> -- 
> Ben Hutchings
> Klipstein's 4th Law of Prototyping and Production:
>                                     A fail-safe circuit will destroy others.
diff mbox

Patch

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 4b9e4aba11b0..c57fa4c74c94 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1272,6 +1272,7 @@  int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	int peeked, off = 0;
 	int err;
 	int is_udplite = IS_UDPLITE(sk);
+	bool checksum_valid = false;
 	bool slow;
 
 	if (flags & MSG_ERRQUEUE)
@@ -1297,11 +1298,12 @@  try_again:
 	 */
 
 	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) {
-		if (udp_lib_checksum_complete(skb))
+		checksum_valid = !udp_lib_checksum_complete(skb);
+		if (!checksum_valid)
 			goto csum_copy_err;
 	}
 
-	if (skb_csum_unnecessary(skb))
+	if (checksum_valid || skb_csum_unnecessary(skb))
 		err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
 					      msg->msg_iov, copied);
 	else {
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index eb38829d8919..e432f8eb3c60 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -389,6 +389,7 @@  int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
 	int peeked, off = 0;
 	int err;
 	int is_udplite = IS_UDPLITE(sk);
+	bool checksum_valid = false;
 	int is_udp4;
 	bool slow;
 
@@ -420,11 +421,12 @@  try_again:
 	 */
 
 	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) {
-		if (udp_lib_checksum_complete(skb))
+		checksum_valid = !udp_lib_checksum_complete(skb);
+		if (!checksum_valid)
 			goto csum_copy_err;
 	}
 
-	if (skb_csum_unnecessary(skb))
+	if (checksum_valid || skb_csum_unnecessary(skb))
 		err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
 					      msg->msg_iov, copied);
 	else {