CVE-2026-64575: bpf: tcp: fix double sock release on batch realloc

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

bpf: tcp: fix double sock release on batch realloc

bpf_iter_tcp_batch() releases the current batch via
bpf_iter_tcp_put_batch(), which drops the socket refs and rewrites
each slot with the socket cookie, then grows the batch. cur_sk/end_sk
are kept for bpf_iter_tcp_resume(), but on realloc failure the function
returns ERR_PTR() before resume runs, leaving cur_sk < end_sk over
slots that now hold cookies rather than sock pointers.
bpf_iter_tcp_seq_stop() then calls bpf_iter_tcp_put_batch() again and
dereferences a cookie as a struct sock.

Empty the batch on the failure path so stop() does not release it
again. The sockets were already freed by the first
bpf_iter_tcp_put_batch(), so nothing leaks, and a later read() rescans
the bucket from the start instead of skipping it. The sibling
GFP_NOWAIT failure path still holds real socket references and is left
for stop() to release.

  BUG: KASAN: null-ptr-deref in __sock_gen_cookie
  Read of size 8 at addr 0000000000000059 by task exploit
   ...
   __sock_gen_cookie (net/core/sock_diag.c:28)
   bpf_iter_tcp_put_batch (net/ipv4/tcp_ipv4.c:2918)
   bpf_iter_tcp_seq_stop (net/ipv4/tcp_ipv4.c:3270)
   bpf_seq_read (kernel/bpf/bpf_iter.c:205)
   vfs_read (fs/read_write.c:572)
   ksys_read (fs/read_write.c:716)
   do_syscall_64
   entry_SYSCALL_64_after_hwframe
  Kernel panic - not syncing: Fatal exception

The Linux kernel CVE team has assigned CVE-2026-64575 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.17 with commit cdec67a489d4fdae3e83e04fca0419136a83c4c2 and fixed in 6.18.42 with commit 9f27c4f0ae35b5390ce4f7a54d3501144e41a54d
	Issue introduced in 6.17 with commit cdec67a489d4fdae3e83e04fca0419136a83c4c2 and fixed in 7.1.6 with commit 8a726e9585ffe7bfbfad2b5279277a00973970f3
	Issue introduced in 6.17 with commit cdec67a489d4fdae3e83e04fca0419136a83c4c2 and fixed in 7.2-rc5 with commit 980a813452754f8001704744e92f7aa697c53dd3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64575
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/ipv4/tcp_ipv4.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/9f27c4f0ae35b5390ce4f7a54d3501144e41a54d
	https://git.kernel.org/stable/c/8a726e9585ffe7bfbfad2b5279277a00973970f3
	https://git.kernel.org/stable/c/980a813452754f8001704744e92f7aa697c53dd3