[PATCH net] llc: fix data loss when reading from a socket in llc_ui_recvmsg()

[PATCH net] llc: fix data loss when reading from a socket in llc_ui_recvmsg()

[Ilia Gavrilov]

For SOCK_STREAM sockets, if user buffer size (len) is less
than skb size (skb->len), the remaining data from skb
will be lost after calling kfree_skb().

To fix this, move the statement for partial reading
above skb deletion.

Found by InfoTeCS on behalf of Linux Verification Center (linuxtesting.org)

Fixes: 30a584d944fb ("[LLX]: SOCK_DGRAM interface fixes")
Cc: stable@vger.kernel.org
Signed-off-by: Ilia Gavrilov <Ilia.Gavrilov@infotecs.ru>
---
 net/llc/af_llc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index 0259cde394ba..cc77ec5769d8 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -887,15 +887,15 @@ static int llc_ui_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 		if (sk->sk_type != SOCK_STREAM)
 			goto copy_uaddr;
 
+		/* Partial read */
+		if (used + offset < skb_len)
+			continue;
+
 		if (!(flags & MSG_PEEK)) {
 			skb_unlink(skb, &sk->sk_receive_queue);
 			kfree_skb(skb);
 			*seq = 0;
 		}
-
-		/* Partial read */
-		if (used + offset < skb_len)
-			continue;
 	} while (len > 0);
 
 out:
-- 
2.39.5

Re: [PATCH net] llc: fix data loss when reading from a socket in llc_ui_recvmsg()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by David S. Miller <davem@davemloft.net>:

On Thu, 15 May 2025 12:20:15 +0000 you wrote:
> For SOCK_STREAM sockets, if user buffer size (len) is less
> than skb size (skb->len), the remaining data from skb
> will be lost after calling kfree_skb().
> 
> To fix this, move the statement for partial reading
> above skb deletion.
> 
> [...]

Here is the summary with links:
  - [net] llc: fix data loss when reading from a socket in llc_ui_recvmsg()
    https://git.kernel.org/netdev/net/c/239af1970bcb

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html