From: Eric Dumazet <eduma...@google.com>
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 <eduma...@google.com>
---
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 {
--
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