mptcp: fix MSG_PEEK stream corruption

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>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 655a2a45224ff03512ab389a8533ec1a4717abdf..2535788569ab3699cd8e1c4e22916034dc2508ae 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1945,22 +1945,36 @@ 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)) {
@@ -1977,16 +1991,14 @@ 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;
@@ -1994,7 +2006,6 @@ 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)
@@ -2191,7 +2202,8 @@ 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;