From: Willem de Bruijn <willemdebruijn.kernel@gmail•com>
To: mheib@redhat•com, netdev@vger•kernel.org
Cc: willemdebruijn.kernel@gmail•com, davem@davemloft•net,
edumazet@google•com, kuba@kernel•org, pabeni@redhat•com,
horms@kernel•org, kernelxing@tencent•com, kuniyu@google•com,
atenart@kernel•org, aleksander.lobakin@intel•com,
Mohammad Heib <mheib@redhat•com>
Subject: Re: [PATCH net v3] net: fix memory leak in skb_segment_list for GRO packets
Date: Mon, 05 Jan 2026 14:34:08 -0500 [thread overview]
Message-ID: <willemdebruijn.kernel.7b8203e93a89@gmail.com> (raw)
In-Reply-To: <20260104213101.352887-1-mheib@redhat.com>
mheib@ wrote:
> From: Mohammad Heib <mheib@redhat•com>
>
> When skb_segment_list() is called during packet forwarding, it handles
> packets that were aggregated by the GRO engine.
>
> Historically, the segmentation logic in skb_segment_list assumes that
> individual segments are split from a parent SKB and may need to carry
> their own socket memory accounting. Accordingly, the code transfers
> truesize from the parent to the newly created segments.
>
> Prior to commit ed4cccef64c1 ("gro: fix ownership transfer"), this
> truesize subtraction in skb_segment_list() was valid because fragments
> still carry a reference to the original socket.
>
> However, commit ed4cccef64c1 ("gro: fix ownership transfer") changed
> this behavior by ensuring that fraglist entries are explicitly
> orphaned (skb->sk = NULL) to prevent illegal orphaning later in the
> stack. This change meant that the entire socket memory charge remained
> with the head SKB, but the corresponding accounting logic in
> skb_segment_list() was never updated.
>
> As a result, the current code unconditionally adds each fragment's
> truesize to delta_truesize and subtracts it from the parent SKB. Since
> the fragments are no longer charged to the socket, this subtraction
> results in an effective under-count of memory when the head is freed.
> This causes sk_wmem_alloc to remain non-zero, preventing socket
> destruction and leading to a persistent memory leak.
>
> The leak can be observed via KMEMLEAK when tearing down the networking
> environment:
>
> unreferenced object 0xffff8881e6eb9100 (size 2048):
> comm "ping", pid 6720, jiffies 4295492526
> backtrace:
> kmem_cache_alloc_noprof+0x5c6/0x800
> sk_prot_alloc+0x5b/0x220
> sk_alloc+0x35/0xa00
> inet6_create.part.0+0x303/0x10d0
> __sock_create+0x248/0x640
> __sys_socket+0x11b/0x1d0
>
> Since skb_segment_list() is exclusively used for SKB_GSO_FRAGLIST
> packets constructed by GRO, the truesize adjustment is removed.
>
> The call to skb_release_head_state() must be preserved. As documented in
> commit cf673ed0e057 ("net: fix fraglist segmentation reference count
> leak"), it is still required to correctly drop references to SKB
> extensions that may be overwritten during __copy_skb_header().
>
> Fixes: ed4cccef64c1 ("gro: fix ownership transfer")
> Signed-off-by: Mohammad Heib <mheib@redhat•com>
Reviewed-by: Willem de Bruijn <willemb@google•com>
next prev parent reply other threads:[~2026-01-05 19:34 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-04 21:31 [PATCH net v3] net: fix memory leak in skb_segment_list for GRO packets mheib
2026-01-05 19:34 ` Willem de Bruijn [this message]
2026-01-06 1:10 ` patchwork-bot+netdevbpf
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