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Miller" , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , Shuah Khan , Willem de Bruijn , Wei Wang , Shakeel Butt , netdev@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Octavian Purdila Content-Type: text/plain; charset="UTF-8" This series fixes a bug discovered in production in tcp_wmem_schedule() where a negative sk->sk_forward_alloc under TCP memory pressure causes tcp_wmem_schedule() to return a negative copy length when sk->sk_wmem_queued already reaches or exceeds sysctl_tcp_wmem[0]. sk->sk_forward_alloc can transiently become negative when tcp_collapse() re-packs partially read or high payload-to-truesize SKBs in the receive queue and charges newly allocated SKBs via sk_mem_charge() before freeing the original SKBs. When a subsequent send hits memory pressure in sk_wmem_schedule() with sk->sk_wmem_queued >= sysctl_tcp_wmem[0], tcp_wmem_schedule() returns min(copy, sk->sk_forward_alloc) < 0. Callers such as tcp_sendmsg_locked() then pass that negative copy length to skb_copy_to_page_nocache() -> copy_from_iter_full() -> check_copy_size(), triggering WARN_ON_ONCE(bytes > INT_MAX) in production and returning -EFAULT instead of waiting for memory or returning -EAGAIN. Patch 1 clamps the return value of tcp_wmem_schedule() to [0, copy] so a negative sk->sk_forward_alloc is treated as 0 available bytes. Patch 2 adds a packetdrill selftest that reproduces the negative sk->sk_forward_alloc condition via tcp_collapse() under memory pressure and verifies that a non-blocking write fails with EAGAIN rather than EFAULT. Changes in v3: - Fix packetdrill test failure in netdev CI (CONFIG_MAX_SKB_FRAGS=17): adjust segment sizes (35 KB) and buffer limits so the receive SKB truesize is identical across CONFIG_MAX_SKB_FRAGS=17 and 45, and tcp_collapse() deterministically drives sk_forward_alloc below -16 KB without invoking the memcg OOM killer. Changes in v2: - Include production warning trace in Patch 1 commit message. - Skip the packetdrill test when PAGE_SIZE != 4096 via --define=REQUIRES_PAGESIZE="4096" in ksft_runner.sh. - Collect Reviewed-by tags from Kuniyuki Iwashima and Eric Dumazet. Octavian Purdila (2): tcp: clamp return value of tcp_wmem_schedule() to non-negative selftests: net: packetdrill: add test for negative sk_forward_alloc in tcp_wmem_schedule() net/ipv4/tcp.c | 2 +- .../testing/selftests/net/packetdrill/config | 2 + .../selftests/net/packetdrill/ksft_runner.sh | 6 + .../tcp_wmem_schedule_negative_fwd_alloc.pkt | 108 ++++++++++++++++++ 4 files changed, 117 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_wmem_schedule_negative_fwd_alloc.pkt -- 2.56.0.307.g5fe7bd680c-goog