CVE-2026-74589: bpf, sockmap: Fix sk_redir use-after-free in send verdict

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

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

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

bpf, sockmap: Fix sk_redir use-after-free in send verdict

sk_psock_msg_verdict() takes a socket reference for psock->sk_redir.
tcp_bpf_send_verdict() copies that pointer while holding the source socket
lock, but does not take a reference for the local copy before dropping the
lock around tcp_bpf_sendmsg_redir().

When apply_bytes keeps the cached verdict active, another sendmsg() on the
same source socket can consume the remaining bytes and release the cached
reference while the first thread still holds only the raw local pointer:

  CPU 0                                  CPU 1
  sk_redir = psock->sk_redir
  apply_bytes remains nonzero
  release_sock(sk)
                                         lock_sock(sk)
                                         apply_bytes reaches zero
                                         psock->sk_redir = NULL
                                         release_sock(sk)
                                         tcp_bpf_sendmsg_redir(sk_redir)
                                         sock_put(sk_redir)
  tcp_bpf_sendmsg_redir(sk_redir)

The final sock_put() can free sk_redir before CPU 0 dereferences it.

KASAN reported:

  BUG: KASAN: slab-use-after-free in tcp_bpf_sendmsg_redir+0xf39/0x1020
  Read of size 8 at addr ffff888108537090 by task poc/87
  Call Trace:
   tcp_bpf_sendmsg_redir+0xf39/0x1020
   tcp_bpf_sendmsg+0x977/0x1a50
   __sys_sendto+0x32c/0x3a0
   __x64_sys_sendto+0xdb/0x1b0
  Allocated by task 85:
   sk_prot_alloc+0x56/0x210
   sk_clone+0x6f/0x14b0
   inet_csk_clone_lock+0x24/0x740
   tcp_create_openreq_child+0x25/0x2710
   tcp_v4_syn_recv_sock+0x10a/0xe00
  Freed by task 0:
   __kasan_slab_free+0x43/0x70
   slab_free_after_rcu_debug+0xa6/0x1e0
   rcu_core+0x50a/0x1850
  Last potentially related work creation:
   __sk_destruct+0x3da/0x540
   sk_psock_destroy+0x81e/0xab0
   process_one_work+0x63a/0x1070

Take a temporary socket reference while the source socket lock still
protects psock->sk_redir, and drop it after tcp_bpf_sendmsg_redir()
returns.  This keeps each unlocked use independent of cached-verdict
ownership.

The Linux kernel CVE team has assigned CVE-2026-74589 to this issue.


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

	Issue introduced in 4.20 with commit 604326b41a6fb9b4a78b6179335decee0365cd8c and fixed in 5.10.265 with commit 41b7da0cb72ca5aa1e62b68dab323d0791fc6bdf
	Issue introduced in 4.20 with commit 604326b41a6fb9b4a78b6179335decee0365cd8c and fixed in 5.15.216 with commit 9b4fbc371a6ecf1b4e43b5a629015cc0830d8de3
	Issue introduced in 4.20 with commit 604326b41a6fb9b4a78b6179335decee0365cd8c and fixed in 6.1.183 with commit 90a19b0894ba79a699b48cf44421b36fbd566e99
	Issue introduced in 4.20 with commit 604326b41a6fb9b4a78b6179335decee0365cd8c and fixed in 6.6.152 with commit d192cff2a37d59206dabe6ec2e60ceac6271f274
	Issue introduced in 4.20 with commit 604326b41a6fb9b4a78b6179335decee0365cd8c and fixed in 6.12.104 with commit 4c9d9aa809c261dc0490a0e19d675f7e8e4c85bf
	Issue introduced in 4.20 with commit 604326b41a6fb9b4a78b6179335decee0365cd8c and fixed in 6.18.45 with commit a14e4ef1d90c3418f01b3b6b8fd3a40a0a208a10
	Issue introduced in 4.20 with commit 604326b41a6fb9b4a78b6179335decee0365cd8c and fixed in 7.1.9 with commit 1cec526cf0a2227395f2c2f4b671cb052ff0b00e
	Issue introduced in 4.20 with commit 604326b41a6fb9b4a78b6179335decee0365cd8c and fixed in 7.2 with commit a76624733730e541e4955fdecf506af2f6b20558

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-2026-74589
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_bpf.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/41b7da0cb72ca5aa1e62b68dab323d0791fc6bdf
	https://git.kernel.org/stable/c/9b4fbc371a6ecf1b4e43b5a629015cc0830d8de3
	https://git.kernel.org/stable/c/90a19b0894ba79a699b48cf44421b36fbd566e99
	https://git.kernel.org/stable/c/d192cff2a37d59206dabe6ec2e60ceac6271f274
	https://git.kernel.org/stable/c/4c9d9aa809c261dc0490a0e19d675f7e8e4c85bf
	https://git.kernel.org/stable/c/a14e4ef1d90c3418f01b3b6b8fd3a40a0a208a10
	https://git.kernel.org/stable/c/1cec526cf0a2227395f2c2f4b671cb052ff0b00e
	https://git.kernel.org/stable/c/a76624733730e541e4955fdecf506af2f6b20558