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* [PATCH mptcp-next v19 0/5] Reduce the differences between TCP and MPTCP for TLS usage
@ 2026-10-30 12:06 Geliang Tang
  2026-10-30 12:06 ` [PATCH mptcp-next v19 1/5] mptcp: drop the mptcp_ooo_try_coalesce() helper Geliang Tang
                   ` (5 more replies)
  0 siblings, 6 replies; 12+ messages in thread
From: Geliang Tang @ 2026-10-30 12:06 UTC (permalink / raw)
  To: mptcp; +Cc: Geliang Tang

From: Geliang Tang <tanggeliang@kylinos.cn>

v19:
 - Replace mptcp_iasn() computed function with msk->tfo_iasn immutable
   snapshot (set in subflow_set_remote_key()), removing tfo_skb_len field
   and the DATA_FIN off-by-one concern.
 - Move MPTCP_SYNC_SEQ handling (test_and_clear_bit + copied_seq update)
   out of __mptcp_sync_rcv_sequence() into callers, since the function
   can be called without the socket lock held.
 - Patch 2: move MPTCP_SYNC_SEQ check in mptcp_release_cb() from
   post-loop to loop start (before backlog spooling). Add the same
   check in mptcp_move_skbs() to sync copied_seq before backlog
   processing when user holds the socket lock.
 - Patch 4: clamp max_seq to ack_seq in mptcp_data_queue_ofo() to
   prevent 64-bit after64() wrap-around when ack_seq > rcv_wnd_sent.

v18:
 - Re-add patch 2 "mptcp: drop the cant_coalesce CB field".
 - Patch 3: simplify TFO sync by relying on patch 2's __mptcp_sync_rcv_sequence()
   instead of complex copied_seq checks. Use copied_seq += mptcp_iasn(msk).
 - Patch 4: move subflow.c changes to patch 2, use map_seq64 for TFO init.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1793349369.git.geliang@kernel.org/

v17:
 - Patch 2: add TFO synchronization: subflow_set_remote_key() preserves
   partial read progress by checking copied_seq against the initial TFO
   value before updating. Add WRITE_ONCE/READ_ONCE for ordering between
   BH (3rd ACK processing) and user-space readers. Add underflow guard
   (copied_seq >= map_seq) before offset subtraction in
   __mptcp_recvmsg_mskq() to protect MSG_PEEK traversals. Skip skbs
   entirely before copied_seq. Update subflow.c to set both map_seq
   (u32) and map_seq64 (u64) for TFO.
 - Patch 3: adapt to the new map_seq (u32) + map_seq64 (u64) layout
   introduced in patch 2.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1793326853.git.tanggeliang@kylinos.cn/

v16:
 - Simplified the series to retain only the core changes required by both
   kTLS and sockmap: drop the CB offset field, add copied_seq tracking,
   and sync the MPTCP skb CB layout with the TCP one.
 - Dropped patch 2, leaving the fastopen code unchanged.
 - Moved patches 6-11 into a separate series "prepare interfaces for kTLS
   and sockmap support".
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1793255126.git.tanggeliang@kylinos.cn/

v15:
 - Patch 2: drop mptcp_data_lock() in mptcp_inq_hint(), use READ_ONCE()
   and __test_and_clear_bit() instead. This issue is unrelated to this
   series and will be addressed in a separate patch later.
 - Patch 5: Guard mptcp_cleanup_rbuf() with read_copied > 0. Initialize/
   reset msk->read_copied. Drop redundant mptcp_recv_skb() in
   __mptcp_read_sock().
 - Patch 6: simplify memory ordering, drop smp_mb()/smp_rmb(), keep
   existing smp_mb__before_atomic(). Check SOCK_DONE inline.
 - Patch 9: drop tcp_sock_rate_check_app_limited() split, call
   tcp_rate_check_app_limited() directly as Paolo suggested. Add
   write_seq != snd_nxt early bail-out.
 - Patch 10: wrap assertion behind expect_all_features().
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1792718041.git.tanggeliang@kylinos.cn/

v14:
 - v13 can no longer be applied to the export branch, so it has been
   rebased here with the following corrections:
 - Patch 2: move locking in mptcp_inq_hint() to avoid races with ack_seq
   change from patch 3 to here. Update commit log.
 - Patch 3: add mptcp_data_lock() in __mptcp_move_skb() around copied_seq
   update. Remove local delta variable in __mptcp_ofo_queue(). Initialize
   msk->copied_seq to 0 in mptcp_propagate_state() fallback path.
 - Patch 4: add map_seq64 comparison in __mptcp_try_coalesce() for 64-bit
   sequence consistency.
 - New patch 11: rename mptcp_check_readable to mptcp_stream_is_readable,
   and align with TCP by calling sk_is_readable() for KTLS support.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1790734083.git.tanggeliang@kylinos.cn/

v13:
 - use smp_mb instead of smp_mb__before_atomic in mptcp_check_data_fin.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1788245079.git.tanggeliang@kylinos.cn/

v12:
 - Move sock_set_flag(SOCK_DONE) to after smp_mb__before_atomic() in
   mptcp_check_data_fin() and reuse the existing barrier rather than adding
   a new smp_wmb().
 - Sample SOCK_DONE before smp_rmb() in mptcp_inq_hint() and mptcp_inq(),
   so the smp_rmb() only orders SOCK_DONE read relative to the subsequent
   ack_seq/copied_seq reads.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1788171508.git.tanggeliang@kylinos.cn/

v11:
 - __mptcp_move_skb(): gate __mptcp_sync_rcv_sequence() on
   test_and_clear_bit(MPTCP_SYNC_SEQ) so the dummy mapping is only re-based
   after ack_seq = iasn.
 - a new patch to set and test SOCK_DONE.
 - use SOCK_DONE in mptcp_inq_hint() and mptcp_inq().
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1788099847.git.tanggeliang@kylinos.cn/

v10:
 - Drop "mptcp: use atomic64_t for locklessly accessed u64 fields"
   (v9 patch 1) and the squash to bpf_burst test (v9 patch 11).
   Series reduced from 11 to 9 patches.
 - Revert all atomic64_read()/atomic64_set() on msk->ack_seq back to
   plain reads and WRITE_ONCE() in patches 1-4. Remove the local u64
   ack_seq variables that only existed to hold atomic64_read() results.
 - mptcp_inq_hint: move test_bit(MPTCP_SYNC_SEQ) inside mptcp_data_lock()
   to close the race between the flag check and the ack_seq read. Revert
   atomic64_read() to plain msk->ack_seq under the lock.
 - mptcp_inq (patch 6): use READ_ONCE() for both ack_seq and copied_seq
   instead of atomic64_read(). Add comment for the FIN subtraction,
   mirroring tcp_inq(). Update commit log.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1787888115.git.tanggeliang@kylinos.cn/

v9:
 - Extend atomic64_t conversion from only msk->ack_seq to all locklessly
   accessed u64 fields: write_seq, snd_nxt, snd_una, wnd_end,
   bytes_received, bytes_consumed.
 - Add mptcp_data_lock() in mptcp_inq_hint() to read ack_seq and
   copied_seq atomically.
 - Add read_copied field and drain it under mptcp_data_lock() in
   mptcp_read_complete() to fix the BH vs worker data race.
 - New patches: mptcp_inq/peek_len and sendmsg_locked proto_ops.
 - Squash to "selftests/bpf: Add bpf_burst scheduler & test".
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1787827525.git.tanggeliang@kylinos.cn/

v8:
 - check MPTCP_SYNC_SEQ in mptcp_inq_hint:
       if (hint_val >= INT_MAX) {
               if (test_bit(MPTCP_SYNC_SEQ, &msk->cb_flags))
                       return 0;
               return INT_MAX;
       }
 - rename mptcp_sock_rate_check_app_limited to
   mptcp_rate_check_app_limited.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1787644449.git.tanggeliang@kylinos.cn/

v7:
 - Patch 1 is a new one to fix the existing issue Sashiko mentioned -
   using atomic64_t for msk->ack_seq.
 - Fix the map_subflow_seq setting in fallback mode in patch 4.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1787537436.git.tanggeliang@kylinos.cn/

v6:
 - Memory ordering for MPTCP_SYNC_SEQ: Add smp_wmb() before set_bit() in
   subflow_set_remote_key() and smp_rmb() after test_and_clear_bit() in
   __mptcp_move_skb() and mptcp_release_cb() to prevent data races on
   weakly-ordered architectures, ensuring ack_seq updates are visible
   before the flag is set and readers see the updated sequence after
   observing the flag.
 - Lockdep nested locking: Use lock_sock_fast_nested(ssk) instead of
   lock_sock_fast(ssk) in mptcp_sock_rate_check_app_limited() to suppress
   false positive recursive locking warnings when acquiring subflow socket
   locks while holding the parent MPTCP socket lock.
 - Receive window advertisement order: Swap mptcp_rcv_space_adjust() and
   mptcp_cleanup_rbuf() in mptcp_read_complete() to expand the receive
   buffer before evaluating window updates, ensuring ACKs advertise the
   new (larger) window size instead of delaying the advertisement until
   the next cycle.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1787446274.git.tanggeliang@kylinos.cn/

v5:
 - only patch 3 changed.
 - Fallback offset underflow: Initialize MPTCP sequence space to 0 in
   mptcp_propagate_state() when mp_opt == NULL, ensuring SKB's map_seq
   starts from 0 to match msk->copied_seq and prevent offset calculation
   underflow in fallback mode.
 - Stale peek_seq: Move peek_seq recomputation into the mptcp_move_skbs()
   continue path and add another recomputation after sk_wait_data(),
   ensuring peek_seq stays synchronized with msk->copied_seq updates from
   MPTCP_SYNC_SEQ processing in both paths.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1787368526.git.tanggeliang@kylinos.cn/

v4:
 - mptcp_recvmsg: move the peek_seq recompute from after sk_wait_data()
   to before the mptcp_move_skbs() continue check.
   mptcp_move_skbs() -> __mptcp_move_skb() may shift the head skb's
   map_seq to the IASN frame via __mptcp_sync_rcv_sequence(); if
   'continue' then exits the loop, the recompute is skipped, and the
   next __mptcp_recvmsg_mskq() computes offset with peek_seq in the old
   frame minus map_seq in the new frame. The underflow makes the offset
   test fail and the skb is skipped (and mptcp_recv_skb() actually frees
   the TFO skb via mptcp_eat_recv_skb()).
 - Make all three MPTCP_SYNC_SEQ bit accesses atomic:
   - subflow_set_remote_key:   __set_bit            -> set_bit
   - __mptcp_move_skb:         __test_and_clear_bit -> test_and_clear_bit
   - mptcp_release_cb:         __test_and_clear_bit -> test_and_clear_bit
   The flag is set in BH under mptcp_data_lock() (msk slock held) and
   cleared in user context under lock_sock() slow path (only owned=1,
   slock not held). The non-atomic RMW on the two sides races, which can
   lose the IASN sync.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1787295147.git.tanggeliang@kylinos.cn/

v3:
 - Patch 2, handle "offset" in __mptcp_sync_rcv_sequence().
 - Patch 3, update __mptcp_move_skb() in response to Sashiko comments:

 	if (__test_and_clear_bit(MPTCP_SYNC_SEQ, &msk->cb_flags))
		msk->copied_seq += mptcp_iasn(msk);

 - Patch 4, replace after64() to after() in mptcp_prune_ofo_queue(). The
   pre-existing issue raised by Sashiko regarding changing the type of
   ack_seq to atomic64_t is not addressed in this series.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1786445142.git.tanggeliang@kylinos.cn/

v2:
 - Patch 3, updated in response to Sashiko comments:

        if (unlikely(msk->rcvd_dummy_seq)) {
                msk->copied_seq += mptcp_iasn(msk);
                __mptcp_sync_rcv_sequence(sk);
                /* Release cb() would otherwise re-base copied_seq
                 * again.
                 */
                test_and_clear_bit(MPTCP_SYNC_SEQ, &msk->cb_flags);
        }

        /* Skip the already peeked data. */
        if (offset >= skb->len) {
                *last = skb;
                continue;
        }
 - Patch 5, replaced with Paolo's patch.
 - Patch 6, 7, new patches addressing app-limited conditions.
 - The patch "trim the duplicated skb head at receive enqueue" has been
   dropped, as it is no longer needed after Paolo updated the "mptcp:
   out-of-order queue pruning" series.
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1786158416.git.tanggeliang@kylinos.cn/

v1:
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1785150300.git.tanggeliang@kylinos.cn/

The goal of this series is to reduce the differences between TCP and MPTCP
for TLS usage, in preparation for adding TLS over MPTCP support in the
future.

In previous versions [1], a struct tls_prot_ops was defined to represent
the interface differences between TCP and MPTCP, which contained the
following callbacks:

	struct sk_buff *(*recv_skb)(struct sock *sk, u32 *off);
	bool (*lock_is_held)(struct sock *sk);
	void (*read_done)(struct sock *sk, size_t len);
	u32 (*get_skb_seq)(struct sk_buff *skb);
	int (*skb_get_header)(const struct sk_buff *skb, int offset,
	                      void *to, int len);
	bool (*epollin_ready)(const struct sock *sk);
	void (*check_app_limited)(struct sock *sk);

In reality, some of these callbacks are unnecessary. This series aims to
eliminate the get_skb_seq(), skb_get_header(), and lock_is_held()
callbacks.

The first four patches come from Paolo's "mptcp: address stall under memory
pressure" series v5 [2], with only minor cleanup from my side.

They remove the CB offset field and sync the MPTCP skb CB layout with the
TCP one, so that we can obtain the TCP or MPTCP sequence number in a
unified way, e.g.:

	struct tls_skb_cb {
	    u32 seq;
	};

	#define TLS_SKB_CB(__skb) ((struct tls_skb_cb *)&((__skb)->cb[0]))

This eliminates the need for a separate get_skb_seq() callback.

Building on the removal of the CB offset field, I also added patch 5 that
trims the duplicated skb head at receive enqueue. With that in place, KTLS
can retrieve the record header via skb_copy_bits() directly, so there is no
longer any need for a dedicated MPTCP helper like mptcp_skb_get_header().
The skb_get_header() callback can thus be removed.

Patch 6 defers sk_data_ready to the worker, which avoids recursive locking
when TLS calls back into MPTCP under mptcp_data_lock(). With this change,
the lock_is_held() callback is no longer needed and can be removed.

[1]
https://patchwork.kernel.org/project/mptcp/cover/cover.1782123118.git.tanggeliang@kylinos.cn/
[2]
https://patchwork.kernel.org/project/mptcp/cover/cover.1778446731.git.pabeni@redhat.com/

Geliang Tang (1):
  mptcp: defer read_sock cleanup to mptcp_worker

Paolo Abeni (4):
  mptcp: drop the mptcp_ooo_try_coalesce() helper
  mptcp: drop the cant_coalesce CB field
  mptcp: remove CB offset field
  mptcp: sync mptcp skb cb layout with tcp one

 net/mptcp/fastopen.c |  16 ++-
 net/mptcp/protocol.c | 268 ++++++++++++++++++++++++++-----------------
 net/mptcp/protocol.h |  16 ++-
 net/mptcp/subflow.c  |  19 ++-
 4 files changed, 201 insertions(+), 118 deletions(-)

-- 
2.55.0


^ permalink raw reply	[flat|nested] 12+ messages in thread
* Re: [PATCH mptcp-next v19 4/5] mptcp: sync mptcp skb cb layout with tcp one
@ 2026-11-01  2:02 netdev-bot+sashiko
  0 siblings, 0 replies; 12+ messages in thread
From: netdev-bot+sashiko @ 2026-11-01  2:02 UTC (permalink / raw)
  To: geliang; +Cc: mptcp, tanggeliang, pabeni, kuba

Thank you for your contribution! Sashiko AI review found 3 potential
issue(s) to consider.

Critical: 1 · High: 0 · Medium: 0 · Low: 2

If you believe none of the issues are legitimate, please reply to each
issue of Medium severity or higher and explain why the AI is wrong.
If any of them are legitimate and you plan to respin, please let patchwork
know by including "pw-bot: cr" as a separate line at the end of your reply
(one such reply per series is enough).

- [Critical] mptcp: subtracting offset from map_seq64 in mptcp_init_skb()
  corrupts OFO data
- [Low] The commit message of "mptcp: sync mptcp skb cb layout with tcp
  one" gets its own safety argument wrong in two places.
- [Low] The commit says the new layout makes "fields with a corresponding
  TCP-level data use the same area inside the CB itself".

--

mptcp: sync mptcp skb cb layout with tcp one

This commit narrows the MPTCP skb CB sequence numbers to 32 bits, so that
map_seq, end_seq and flags sit at the same offsets as the matching fields
in struct tcp_skb_cb. A 64-bit map_seq64 copy is kept for the admission
checks. The receive and OFO queue paths now use 32-bit after()/before()
arithmetic, and BUILD_BUG_ON() checks on the CB offsets are added in
mptcp_proto_init().

> The 32-bit sequence numbers are safe because all SKBs in the receive queue
> and OFO queue have been validated against the receive window (max INT_MAX),
> so their sequence numbers are guaranteed to be within 2^31 of the current
> ack_seq or copied_seq. This ensures that 32-bit arithmetic (comparisons
> and subtractions) produces correct results even when 64-bit values cross
> the 2^32 boundary, as the relative distance remains small.
>
> Add build time check to ensure the latter invariant.

[Severity: Low]
Is the last sentence accurate? The only build time check added is
CHK_CB_FIELD() in mptcp_proto_init():

    CHK_CB_FIELD(map_seq, seq);
    CHK_CB_FIELD(end_seq, end_seq);
    CHK_CB_FIELD(flags, tcp_flags);

These compare offsetof()/offsetofend() of the mptcp_skb_cb fields against
struct tcp_skb_cb. That checks the CB layout. Nothing checks the 2^31
sequence distance from the previous paragraph, either at build time or at
run time.

The claim that all skbs in the receive queue were validated against the
receive window also doesn't seem to match __mptcp_move_skb(). In-sequence
and partial skbs go onto sk_receive_queue without any rcv_wnd_sent
comparison:

    if (MPTCP_SKB_CB(skb)->map_seq64 == msk->ack_seq) {
        /* in sequence */
    insert:
        if (!mptcp_try_rmem_schedule(sk, skb)) {
        ...
        __skb_queue_tail(&sk->sk_receive_queue, skb);

The rcv_wnd_sent check exists only in mptcp_data_queue_ofo(). For fallback
sockets, mptcp_can_ingest() also skips the rcvbuf bound on purpose:

    return likely(sk_rmem_alloc_get(sk) <= READ_ONCE(sk->sk_rcvbuf)) ||
           __mptcp_check_fallback(mptcp_sk(sk));

The message also leaves out functional changes that the 32-bit narrowing
appears to depend on:

  - the new after64(MPTCP_SKB_CB(skb)->map_seq64, max_seq) admission check
    in mptcp_data_queue_ofo()
  - clamping max_seq to ack_seq in mptcp_data_queue_ofo()
  - the new 64-bit contiguity check on map_seq64 in __mptcp_try_coalesce()

As far as I can tell the code itself is fine. OFO distances are bounded by
the TCP selected window, and the receive queue offset math only needs
distances below 2^32.

Could the commit message be updated to describe what actually guarantees
the invariant, and what the build time check covers?

[ ... ]

> diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
> index 7878e6ac6c0b6..fa54f70ab501d 100644
> --- a/net/mptcp/protocol.h
> +++ b/net/mptcp/protocol.h
> @@ -129,9 +129,12 @@
>  #define MPTCP_SYNC_SEQ		8
>  
>  struct mptcp_skb_cb {
> -	u64 map_seq;
> -	u64 end_seq;
> +	u32 map_seq;
> +	u32 end_seq;
> +	u32 unused;
> +	u16 flags;
>  	u8  has_rxtstamp;
> +	u64 map_seq64;
>  };

[Severity: Low]
The commit message says the new layout makes fields "with a corresponding
TCP-level data use the same area inside the CB itself". Is that true for
has_rxtstamp?

In struct tcp_skb_cb, has_rxtstamp is a 1-bit field in the byte at
offset 16:

    __u8        txstamp_ack:2,
                eor:1,
                has_rxtstamp:1,
                unused:4;

Offset 14 in struct tcp_skb_cb is sacked.

Here the u8 has_rxtstamp lands at offset 14, on top of TCP's sacked.
map_seq64 takes offsets 16-23, so it overlaps TCP's
txstamp_ack/eor/has_rxtstamp byte and ack_seq. On an msk-level skb,
TCP_SKB_CB(skb)->has_rxtstamp or ->eor would read bits from the low byte
of map_seq64.

CHK_CB_FIELD() in mptcp_proto_init() checks only map_seq, end_seq and
flags, so the build does not catch this.

Nothing reads those TCP fields on msk skbs today. That includes the
following patch, "mptcp: defer read_sock cleanup to mptcp_worker". The
TLS strparser helpers tls_strp_check_queue_ok() and tls_rx_msg_size() use
only TCP_SKB_CB(skb)->seq, and that field is aliased correctly.

Should the commit message say the layout is only partially synced? The
other option is to move has_rxtstamp to match TCP and add it to the
CHK_CB_FIELD() checks.

[ ... ]

> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -421,11 +430,13 @@ static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset)
>  
>  	/* the skb map_seq accounts for the skb offset:
>  	 * mptcp_subflow_get_mapped_dsn() is based on the current tp->copied_seq
> -	 * value
> +	 * value; note that end seq number is only available in 32bits format.
>  	 */
> -	MPTCP_SKB_CB(skb)->map_seq = mptcp_subflow_get_mapped_dsn(subflow) -
> -				     offset;
> +	MPTCP_SKB_CB(skb)->map_seq64 = mptcp_subflow_get_mapped_dsn(subflow) -
> +				       offset;
> +	MPTCP_SKB_CB(skb)->map_seq = (u32)MPTCP_SKB_CB(skb)->map_seq64;
>  	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + skb->len;
> +	MPTCP_SKB_CB(skb)->flags = 0;
>  	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
>  
>  	__skb_unlink(skb, &ssk->sk_receive_queue);

[Severity: Critical]
mptcp_init_skb() assigns DSNs to the whole skb starting at
mptcp_subflow_get_mapped_dsn(subflow) - offset. Here offset is
tp->copied_seq - TCP_SKB_CB(skb)->seq, as computed in
__mptcp_move_skbs_from_subflow(). Only the bytes [offset, skb->len)
belong to the DSS mapping that subflow_check_data_avail() validated
with validate_mapping() and, when checksums are enabled,
validate_data_csum().

The leading [0, offset) bytes are something else. They are either
data dropped by mptcp_subflow_discard_data() for an earlier mapping,
or the overlapping head of a TCP segment that tcp_data_queue() or
tcp_ofo_queue() queued with seq before copied_seq. They can come from
a different mapping. Nothing guarantees that their DSNs are
[mapped_dsn - offset, mapped_dsn), where mapped_dsn is the value
returned by mptcp_subflow_get_mapped_dsn().

When the mapping is in order at the msk level, msk->ack_seq is
already at or past mapped_dsn. The prefix is then skipped by the
partial packet branch in __mptcp_move_skb() and by the read offset in
__mptcp_recvmsg_mskq() and mptcp_recv_skb(). That no longer holds
when mapped_dsn is after msk->ack_seq:

  - If mapped_dsn - offset is at or before msk->ack_seq,
    __mptcp_move_skb() takes the in-sequence or partial packet
    branch. The skb is queued on (or coalesced into)
    sk_receive_queue, and msk->ack_seq moves across
    [msk->ack_seq, mapped_dsn), which was never received. recvmsg
    then returns the stale prefix bytes for that range.

  - Otherwise mptcp_data_queue_ofo() puts the skb in the OFO tree
    starting at mapped_dsn - offset. When the real data for
    [mapped_dsn - offset, mapped_dsn) arrives later on another
    subflow, it is dropped as MPTCP_MIB_DUPDATA. Also,
    __mptcp_try_coalesce() can append the prefix to a preceding OFO
    skb that ends at mapped_dsn - offset. __mptcp_ofo_queue() moves
    the skb to the receive queue once msk->ack_seq reaches
    mapped_dsn - offset.

In both cases user space silently gets corrupted stream data, and the
prefix never went through the DSS checksum. A peer can trigger this
by sending an out-of-order mapping on a subflow whose head skb has a
non-zero offset.

The subtraction is not new here: the old 64-bit map_seq was computed
the same way. This patch does rewrite these lines, though, and now
derives map_seq, end_seq and map_seq64 from the same shifted base.
Should the prefix be pulled off the skb before it lands in the msk
queues, at least when the mapping is ahead of msk->ack_seq? Or is
there something I am missing that rules out a non-zero offset in that
case?

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/cover.1793361629.git.tanggeliang%40kylinos.cn

^ permalink raw reply	[flat|nested] 12+ messages in thread
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Thread overview: 12+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-10-30 12:06 [PATCH mptcp-next v19 0/5] Reduce the differences between TCP and MPTCP for TLS usage Geliang Tang
2026-10-30 12:06 ` [PATCH mptcp-next v19 1/5] mptcp: drop the mptcp_ooo_try_coalesce() helper Geliang Tang
2026-10-30 12:06 ` [PATCH mptcp-next v19 2/5] mptcp: drop the cant_coalesce CB field Geliang Tang
2026-10-30 12:29   ` sashiko-bot
2026-10-30 12:06 ` [PATCH mptcp-next v19 3/5] mptcp: remove CB offset field Geliang Tang
2026-10-30 12:52   ` sashiko-bot
2026-10-30 12:06 ` [PATCH mptcp-next v19 4/5] mptcp: sync mptcp skb cb layout with tcp one Geliang Tang
2026-10-30 12:39   ` sashiko-bot
2026-10-30 12:06 ` [PATCH mptcp-next v19 5/5] mptcp: defer read_sock cleanup to mptcp_worker Geliang Tang
2026-10-30 12:56   ` sashiko-bot
2026-10-30 14:06 ` [PATCH mptcp-next v19 0/5] Reduce the differences between TCP and MPTCP for TLS usage MPTCP CI
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2026-11-01  2:02 [PATCH mptcp-next v19 4/5] mptcp: sync mptcp skb cb layout with tcp one netdev-bot+sashiko

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