[PATCH v2] audit: Initialize lsmctx to avoid memory allocation error

[Paul Moore]

On Jan 25, 2025 Huacai Chen <chenhuacai at loongson.cn> wrote:
> 
> Initialize the local variable lsmctx in audit_receive_msg(), so as to
> avoid memory allocation errors like:
> 
> [  258.074914] WARNING: CPU: 2 PID: 443 at mm/page_alloc.c:4727 __alloc_pages_noprof+0x4c8/0x1040
> [  258.074997] pc 900000000304d588 ra 9000000003059644 tp 9000000107774000 sp 9000000107777890
> [  258.075000] a0 0000000000040cc0 a1 0000000000000012 a2 0000000000000000 a3 0000000000000000
> [  258.075003] a4 9000000107777bd0 a5 0000000000000280 a6 0000000000000010 a7 0000000000000000
> [  258.075006] t0 9000000004b4c000 t1 0000000000000001 t2 1f3f37829c264c80 t3 000000000000002e
> [  258.075009] t4 0000000000000000 t5 00000000000003f6 t6 90000001066b6310 t7 000000000000002f
> [  258.075011] t8 000000000000003c u0 00000000000000b4 s9 900000010006f880 s0 9000000004a4b000
> [  258.075014] s1 0000000000000000 s2 9000000004a4b000 s3 9000000106673400 s4 9000000107777af0
> [  258.075017] s5 90000001066b6300 s6 0000000000000012 s7 fffffffffffff000 s8 0000000000000004
> [  258.075019]    ra: 9000000003059644 ___kmalloc_large_node+0x84/0x1e0
> [  258.075026]   ERA: 900000000304d588 __alloc_pages_noprof+0x4c8/0x1040
> [  258.075030]  CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
> [  258.075040]  PRMD: 00000004 (PPLV0 +PIE -PWE)
> [  258.075045]  EUEN: 00000007 (+FPE +SXE +ASXE -BTE)
> [  258.075051]  ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7)
> [  258.075056] ESTAT: 000c0000 [BRK] (IS= ECode=12 EsubCode=0)
> [  258.075061]  PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)
> [  258.075064] CPU: 2 UID: 0 PID: 443 Comm: auditd Not tainted 6.13.0-rc1+ #1899
> [  258.075070] Stack : ffffffffffffffff 0000000000000000 9000000002debf5c 9000000107774000
> [  258.075077]         90000001077774f0 0000000000000000 90000001077774f8 900000000489e480
> [  258.075083]         9000000004b380e8 9000000004b380e0 9000000107777380 0000000000000001
> [  258.075089]         0000000000000001 9000000004a4b000 1f3f37829c264c80 90000001001a9b40
> [  258.075094]         9000000107774000 9000000004b080e8 00000000000003d4 9000000004b080e8
> [  258.075100]         9000000004a580e8 000000000000002d 0000000006ebc000 900000010006f880
> [  258.075106]         00000000000000b4 0000000000000000 0000000000000004 0000000000001277
> [  258.075112]         900000000489e480 90000001066b6300 0000000000000012 fffffffffffff000
> [  258.075118]         0000000000000004 900000000489e480 9000000002def6a8 00007ffff2ba4065
> [  258.075124]         00000000000000b0 0000000000000004 0000000000000000 0000000000071c1d
> [  258.075129]         ...
> [  258.075132] Call Trace:
> [  258.075135] [<9000000002def6a8>] show_stack+0x30/0x148
> [  258.075146] [<9000000002debf58>] dump_stack_lvl+0x68/0xa0
> [  258.075152] [<9000000002e0fe18>] __warn+0x80/0x108
> [  258.075158] [<900000000407486c>] report_bug+0x154/0x268
> [  258.075163] [<90000000040ad468>] do_bp+0x2a8/0x320
> [  258.075172] [<9000000002dedda0>] handle_bp+0x120/0x1c0
> [  258.075178] [<900000000304d588>] __alloc_pages_noprof+0x4c8/0x1040
> [  258.075183] [<9000000003059640>] ___kmalloc_large_node+0x80/0x1e0
> [  258.075187] [<9000000003061504>] __kmalloc_noprof+0x2c4/0x380
> [  258.075192] [<9000000002f0f7ac>] audit_receive_msg+0x764/0x1530
> [  258.075199] [<9000000002f1065c>] audit_receive+0xe4/0x1c0
> [  258.075204] [<9000000003e5abe8>] netlink_unicast+0x340/0x450
> [  258.075211] [<9000000003e5ae9c>] netlink_sendmsg+0x1a4/0x4a0
> [  258.075216] [<9000000003d9ffd0>] __sock_sendmsg+0x48/0x58
> [  258.075222] [<9000000003da32f0>] __sys_sendto+0x100/0x170
> [  258.075226] [<9000000003da3374>] sys_sendto+0x14/0x28
> [  258.075229] [<90000000040ad574>] do_syscall+0x94/0x138
> [  258.075233] [<9000000002ded318>] handle_syscall+0xb8/0x158

If you are going to include the backtrace, please ensure that the lines
do not wrap when viewing the commit using 'git log' in an 80 char wide
terminal.

> Root cause: if we enable AUDIT but disable LSM, in the AUDIT_SIGNAL_INFO
> case, lsmprop_is_set() returns false, then kmalloc() may try to allocate
> a large amount of memory with an uninitialized length.

You shouldn't need to have a special "Root cause:" section, just work
that into the commit description normally.  I would suggest that the
commit description could simply be something like the following:

  When audit is enabled in a kernel build, and there are no LSMs
  active that support LSM labeling, it is possible that the lsmctx
  variable in the AUDIT_SIGNAL_INFO handler in audit_receive_msg()
  could be used before it is properly initialize.  This patch
  corrects this problem by initializing the lsmctx to a safe value
  when it is declared.

> Fixes: 6fba89813ccf333d ("lsm: ensure the correct LSM context releaser")
> Signed-off-by: Huacai Chen <chenhuacai at loongson.cn>
> ---
> V2: Update commit message and CC list.
> 
>  kernel/audit.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 13d0144efaa3..5f5bf85bcc90 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1221,7 +1221,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
>  	struct audit_buffer	*ab;
>  	u16			msg_type = nlh->nlmsg_type;
>  	struct audit_sig_info   *sig_data;
> -	struct lsm_context	lsmctx;
> +	struct lsm_context	lsmctx = { NULL, 0, 0 };
>  
>  	err = audit_netlink_ok(skb, msg_type);
>  	if (err)
> -- 
> 2.47.1

--
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