tcp: fix reordering addition overflow in MTU probing

Commit efb8763d7bbb ("net: ipv4: bound TCP reordering sysctl writes and
MTU probe sizes") widened size_needed and the MSS multiplication, but
tp->reordering + 1 is still evaluated as u32. RTAX_REORDERING accepts
an unrestricted u32, and tcp_init_metrics() can install U32_MAX.

In that case the extra-data requirement becomes zero. A write queue
with probe_size - 1 data bytes and a FIN satisfies the sequence-space
check. The coalescing walk can pass the queue head to
tcp_skb_can_collapse(), and tcp_clone_payload() can produce an skb
whose advertised payload exceeds the data in its fragments. Local
delivery followed by TCP_ZEROCOPY_RECEIVE can then walk beyond the
fragment array. KASAN reports a slab-out-of-bounds read in
can_map_frag().

Cast reordering before incrementing it so the arithmetic handles the
entire u32 metric range. For U32_MAX, the required size exceeds the
32-bit queue and window limits, so the existing checks skip the probe.
The calculation is unchanged for all other reordering values.

Fixes: efb8763d7bbb ("net: ipv4: bound TCP reordering sysctl writes and MTU probe sizes")
Cc: stable@vger.kernel.org
Cc: Wyatt Feng <bronzed_45_vested@icloud.com>
Cc: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Signed-off-by: Eric Dumazet <edumazet@kernel.org>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://patch.msgid.link/20261028160226.2170244-1-edumazet@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions