linux-cve-announce - CVE-2025-21852: net: Add rx_skb of kfree_skb to raw_tp_null

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Message-ID: <2025031213-CVE-2025-21852-b942@gregkh>
Date: Wed, 12 Mar 2025 10:42:18 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21852: net: Add rx_skb of kfree_skb to raw_tp_null_args[].

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

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

net: Add rx_skb of kfree_skb to raw_tp_null_args[].

Yan Zhai reported a BPF prog could trigger a null-ptr-deref [0]
in trace_kfree_skb if the prog does not check if rx_sk is NULL.

Commit c53795d48ee8 ("net: add rx_sk to trace_kfree_skb") added
rx_sk to trace_kfree_skb, but rx_sk is optional and could be NULL.

Let's add kfree_skb to raw_tp_null_args[] to let the BPF verifier
validate such a prog and prevent the issue.

Now we fail to load such a prog:

  libbpf: prog 'drop': -- BEGIN PROG LOAD LOG --
  0: R1=ctx() R10=fp0
  ; int BPF_PROG(drop, struct sk_buff *skb, void *location, @ kfree_skb_sk_null.bpf.c:21
  0: (79) r3 = *(u64 *)(r1 +24)
  func 'kfree_skb' arg3 has btf_id 5253 type STRUCT 'sock'
  1: R1=ctx() R3_w=trusted_ptr_or_null_sock(id=1)
  ; bpf_printk("sk: %d, %d\n", sk, sk->__sk_common.skc_family); @ kfree_skb_sk_null.bpf.c:24
  1: (69) r4 = *(u16 *)(r3 +16)
  R3 invalid mem access 'trusted_ptr_or_null_'
  processed 2 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
  -- END PROG LOAD LOG --

Note this fix requires commit 838a10bd2ebf ("bpf: Augment raw_tp
arguments with PTR_MAYBE_NULL").

[0]:
BUG: kernel NULL pointer dereference, address: 0000000000000010
 PF: supervisor read access in kernel mode
 PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
PREEMPT SMP
RIP: 0010:bpf_prog_5e21a6db8fcff1aa_drop+0x10/0x2d
Call Trace:
 <TASK>
 ? __die+0x1f/0x60
 ? page_fault_oops+0x148/0x420
 ? search_bpf_extables+0x5b/0x70
 ? fixup_exception+0x27/0x2c0
 ? exc_page_fault+0x75/0x170
 ? asm_exc_page_fault+0x22/0x30
 ? bpf_prog_5e21a6db8fcff1aa_drop+0x10/0x2d
 bpf_trace_run4+0x68/0xd0
 ? unix_stream_connect+0x1f4/0x6f0
 sk_skb_reason_drop+0x90/0x120
 unix_stream_connect+0x1f4/0x6f0
 __sys_connect+0x7f/0xb0
 __x64_sys_connect+0x14/0x20
 do_syscall_64+0x47/0xc30
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

The Linux kernel CVE team has assigned CVE-2025-21852 to this issue.

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

	Issue introduced in 6.11 with commit c53795d48ee8f385c6a9e394651e7ee914baaeba and fixed in 6.12.17 with commit f579afacd0a66971fc8481f30d2d377e230a8342
	Issue introduced in 6.11 with commit c53795d48ee8f385c6a9e394651e7ee914baaeba and fixed in 6.13.5 with commit 4dba79c1e7aad6620bbb707b6c4459380fd90860
	Issue introduced in 6.11 with commit c53795d48ee8f385c6a9e394651e7ee914baaeba and fixed in 6.14-rc4 with commit 5da7e15fb5a12e78de974d8908f348e279922ce9

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-2025-21852
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:
	kernel/bpf/btf.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/f579afacd0a66971fc8481f30d2d377e230a8342
	https://git.kernel.org/stable/c/4dba79c1e7aad6620bbb707b6c4459380fd90860
	https://git.kernel.org/stable/c/5da7e15fb5a12e78de974d8908f348e279922ce9