CVE-2026-74715: bpf: Fix netns reference imbalance in conntrack kfuncs

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

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

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

bpf: Fix netns reference imbalance in conntrack kfuncs

The opts argument of the BPF conntrack kfuncs can point to a shared
map value.  __bpf_nf_ct_lookup() and __bpf_nf_ct_alloc_entry() read
opts->netns_id separately when acquiring and releasing the network
namespace reference.

The reference imbalance can occur as follows:

  CPU 0                                  CPU 1
  read opts->netns_id (-1)
  skip get_net_ns_by_id()
                                         write opts->netns_id (id)
  read opts->netns_id (id)
  put_net(net) /* no matching get */

The reverse transition leaks the reference.  Repeating the unmatched put
can destroy a live namespace and crash later users.

The kernel reported:

  Oops: general protection fault, probably for non-canonical address
  KASAN: null-ptr-deref in range [0x00000000000000e8-0x00000000000000ef]
  RIP: 0010:bpf_prog_test_run_xdp+0x52c/0x1700
  Call Trace:
   __sys_bpf+0x1662/0x50c0
   __x64_sys_bpf+0x73/0xb0
   do_syscall_64+0xf9/0x540
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  Kernel panic - not syncing: Fatal exception

Snapshot every input field of opts with READ_ONCE() before validating or
using it.  The netns_id snapshot keeps the namespace get/put pair
balanced, while the other snapshots keep the remaining options from
changing partway through an invocation.  The individual reads can still
observe an inconsistent combination during a concurrent update, but each
selected field value remains stable for that invocation.

The Linux kernel CVE team has assigned CVE-2026-74715 to this issue.


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

	Issue introduced in 6.0 with commit aed8ee7feb44b6537af1e0b4f03365d42928be38 and fixed in 7.1.9 with commit e5e060eb63d10b41ab60fd955649479d99b38210
	Issue introduced in 6.0 with commit aed8ee7feb44b6537af1e0b4f03365d42928be38 and fixed in 7.2 with commit fdeba03fea78407a8c52faa99177c9f7f29f90eb

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-2026-74715
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/netfilter/nf_conntrack_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/e5e060eb63d10b41ab60fd955649479d99b38210
	https://git.kernel.org/stable/c/fdeba03fea78407a8c52faa99177c9f7f29f90eb