From 197c949e7798fbf28cfadc69d9ca0c2abbf93191 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 30 Dec 2015 08:51:12 -0500 Subject: [PATCH] udp: properly support MSG_PEEK with truncated buffers 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 Acked-by: Herbert Xu Signed-off-by: David S. Miller --- net/ipv4/udp.c | 6 ++++-- net/ipv6/udp.c | 6 ++++-- 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 8841e984f8bf..ac14ae44390d 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1271,6 +1271,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock, int peeked, off = 0; int err; int is_udplite = IS_UDPLITE(sk); + bool checksum_valid = false; bool slow; if (flags & MSG_ERRQUEUE) @@ -1296,11 +1297,12 @@ 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_msg(skb, sizeof(struct udphdr), msg, copied); else { diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c index 9da3287a3923..00775ee27d86 100644 --- a/net/ipv6/udp.c +++ b/net/ipv6/udp.c @@ -402,6 +402,7 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int peeked, off = 0; int err; int is_udplite = IS_UDPLITE(sk); + bool checksum_valid = false; int is_udp4; bool slow; @@ -433,11 +434,12 @@ 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_msg(skb, sizeof(struct udphdr), msg, copied); else { -- 2.20.1