CVE-2026-52938: bpf: Fix NULL pointer dereference in bpf_sk_storage_clone and diag paths

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

bpf: Fix NULL pointer dereference in bpf_sk_storage_clone and diag paths

bpf_selem_unlink_nofail() sets SDATA(selem)->smap to NULL before
removing the selem from the storage hlist. A concurrent RCU reader in
bpf_sk_storage_clone() can observe the selem still on the list with
smap already NULL, causing a NULL pointer dereference.

 general protection fault, probably for non-canonical address 0xdffffc000000000a:
 KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057]
 RIP: 0010:bpf_sk_storage_clone+0x1cd/0xaa0 net/core/bpf_sk_storage.c:174
 Call Trace:
  <IRQ>
  sk_clone+0xfed/0x1980 net/core/sock.c:2591
  inet_csk_clone_lock+0x30/0x760 net/ipv4/inet_connection_sock.c:1222
  tcp_create_openreq_child+0x35/0x2680 net/ipv4/tcp_minisocks.c:571
  tcp_v4_syn_recv_sock+0x123/0xf90 net/ipv4/tcp_ipv4.c:1729
  tcp_check_req+0x8e1/0x2580 include/net/tcp.h:855
  tcp_v4_rcv+0x1845/0x3b80 net/ipv4/tcp_ipv4.c:2347

Add a NULL check for smap in bpf_sk_storage_clone().

bpf_sk_storage_diag_put_all() has the same issue. Add a NULL check
and pass the validated smap directly to diag_get(), which is refactored
to take smap as a parameter instead of reading it internally.

bpf_sk_storage_diag_put() uses diag->maps[i] which is always valid
under its refcount, so diag->maps[i] is passed directly to diag_get().

The Linux kernel CVE team has assigned CVE-2026-52938 to this issue.


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

	Issue introduced in 7.0 with commit 5d800f87d0a5ea1b156c47a4b9fd128479335153 and fixed in 7.1 with commit 375e4e33c18dfa05c5dfd5f3dfffeb29343dd4c7

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-2026-52938
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/core/bpf_sk_storage.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/375e4e33c18dfa05c5dfd5f3dfffeb29343dd4c7