mptcp: fix MSG_PEEK stream corruption

[ Upstream commit 8e04ce45a8db7a080220e86e249198fa676b83dc ]

If a MSG_PEEK | MSG_WAITALL read operation consumes all the bytes in the
receive queue and recvmsg() need to waits for more data - i.e. it's a
blocking one - upon arrival of the next packet the MPTCP protocol will
start again copying the oldest data present in the receive queue,
corrupting the data stream.

Address the issue explicitly tracking the peeked sequence number,
restarting from the last peeked byte.

Fixes: ca4fb892579f ("mptcp: add MSG_PEEK support")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Geliang Tang <geliang@kernel.org>
Tested-by: Geliang Tang <geliang@kernel.org>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251028-net-mptcp-send-timeout-v1-2-38ffff5a9ec8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index e4398ee9b55ac82391feb92861693ed6a19a653a..86ca04c6add4146e1af68c31d10981588b340abf 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1892,22 +1892,36 @@ do_error:
 
 static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied);
 
-static int __mptcp_recvmsg_mskq(struct sock *sk,
-                               struct msghdr *msg,
-                               size_t len, int flags,
+static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg,
+                               size_t len, int flags, int copied_total,
                                struct scm_timestamping_internal *tss,
                                int *cmsg_flags)
 {
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *skb, *tmp;
+       int total_data_len = 0;
        int copied = 0;
 
        skb_queue_walk_safe(&sk->sk_receive_queue, skb, tmp) {
-               u32 offset = MPTCP_SKB_CB(skb)->offset;
+               u32 delta, offset = MPTCP_SKB_CB(skb)->offset;
                u32 data_len = skb->len - offset;
-               u32 count = min_t(size_t, len - copied, data_len);
+               u32 count;
                int err;
 
+               if (flags & MSG_PEEK) {
+                       /* skip already peeked skbs */
+                       if (total_data_len + data_len <= copied_total) {
+                               total_data_len += data_len;
+                               continue;
+                       }
+
+                       /* skip the already peeked data in the current skb */
+                       delta = copied_total - total_data_len;
+                       offset += delta;
+                       data_len -= delta;
+               }
+
+               count = min_t(size_t, len - copied, data_len);
                if (!(flags & MSG_TRUNC)) {
                        err = skb_copy_datagram_msg(skb, offset, msg, count);
                        if (unlikely(err < 0)) {
@@ -1924,16 +1938,14 @@ static int __mptcp_recvmsg_mskq(struct sock *sk,
 
                copied += count;
 
-               if (count < data_len) {
-                       if (!(flags & MSG_PEEK)) {
+               if (!(flags & MSG_PEEK)) {
+                       msk->bytes_consumed += count;
+                       if (count < data_len) {
                                MPTCP_SKB_CB(skb)->offset += count;
                                MPTCP_SKB_CB(skb)->map_seq += count;
-                               msk->bytes_consumed += count;
+                               break;
                        }
-                       break;
-               }
 
-               if (!(flags & MSG_PEEK)) {
                        /* avoid the indirect call, we know the destructor is sock_rfree */
                        skb->destructor = NULL;
                        skb->sk = NULL;
@@ -1941,7 +1953,6 @@ static int __mptcp_recvmsg_mskq(struct sock *sk,
                        sk_mem_uncharge(sk, skb->truesize);
                        __skb_unlink(skb, &sk->sk_receive_queue);
                        skb_attempt_defer_free(skb);
-                       msk->bytes_consumed += count;
                }
 
                if (copied >= len)
@@ -2164,7 +2175,8 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
        while (copied < len) {
                int err, bytes_read;
 
-               bytes_read = __mptcp_recvmsg_mskq(sk, msg, len - copied, flags, &tss, &cmsg_flags);
+               bytes_read = __mptcp_recvmsg_mskq(sk, msg, len - copied, flags,
+                                                 copied, &tss, &cmsg_flags);
                if (unlikely(bytes_read < 0)) {
                        if (!copied)
                                copied = bytes_read;