Commit 5ccf7b4d authored by Eric Dumazet's avatar Eric Dumazet Committed by Willy Tarreau

udp: properly support MSG_PEEK with truncated buffers

commit 197c949e upstream.

Backport of this upstream commit into stable kernels :
89c22d8c ("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: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
(cherry picked from commit 18a6eba2)
Signed-off-by: default avatarWilly Tarreau <w@1wt.eu>
parent d699b47f
...@@ -941,6 +941,7 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, ...@@ -941,6 +941,7 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
int peeked; int peeked;
int err; int err;
int is_udplite = IS_UDPLITE(sk); int is_udplite = IS_UDPLITE(sk);
bool checksum_valid = false;
if (flags & MSG_ERRQUEUE) if (flags & MSG_ERRQUEUE)
return ip_recv_error(sk, msg, len, addr_len); return ip_recv_error(sk, msg, len, addr_len);
...@@ -965,11 +966,12 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, ...@@ -965,11 +966,12 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
*/ */
if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) { 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; 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), err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
msg->msg_iov, copied); msg->msg_iov, copied);
else { else {
......
...@@ -198,6 +198,7 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk, ...@@ -198,6 +198,7 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
int peeked; int peeked;
int err; int err;
int is_udplite = IS_UDPLITE(sk); int is_udplite = IS_UDPLITE(sk);
bool checksum_valid = false;
int is_udp4; int is_udp4;
if (flags & MSG_ERRQUEUE) if (flags & MSG_ERRQUEUE)
...@@ -225,11 +226,12 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk, ...@@ -225,11 +226,12 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
*/ */
if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) { 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; 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), err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
msg->msg_iov, copied ); msg->msg_iov, copied );
else { else {
......
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