CVE-2026-22979: net: fix memory leak in skb_segment_list for GRO packets

In the Linux kernel, the following vulnerability has been resolved:

net: fix memory leak in skbsegmentlist for GRO packets

When skbsegmentlist() is called during packet forwarding, it handles packets that were aggregated by the GRO engine.

Historically, the segmentation logic in skbsegmentlist 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 skbsegmentlist() 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 skbsegmentlist() was never updated.

As a result, the current code unconditionally adds each fragment's truesize to deltatruesize 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 skwmemalloc 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: kmemcacheallocnoprof+0x5c6/0x800 skprotalloc+0x5b/0x220 skalloc+0x35/0xa00 inet6create.part.0+0x303/0x10d0 sockcreate+0x248/0x640 syssocket+0x11b/0x1d0

Since skbsegmentlist() is exclusively used for SKBGSOFRAGLIST packets constructed by GRO, the truesize adjustment is removed.

The call to skbreleaseheadstate() 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 copyskbheader().