Re: [PATCH] audit: use supplied gfp_mask from audit_buffer in kauditd_send_multicast_skb

[Paul Moore]

On Thursday, December 18, 2014 11:09:27 PM Richard Guy Briggs wrote:
> Eric Paris explains: Since kauditd_send_multicast_skb() gets called in
> audit_log_end(), which can come from any context (aka even a sleeping
> context) GFP_KERNEL can't be used.  Since the audit_buffer knows what
> context it should use, pass that down and use that.
> 
> See: https://lkml.org/lkml/2014/12/16/542
> 
> BUG: sleeping function called from invalid context at mm/slab.c:2849
> in_atomic(): 1, irqs_disabled(): 0, pid: 885, name: sulogin
> 2 locks held by sulogin/885:
>   #0:  (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff91152e30>]
> prepare_bprm_creds+0x28/0x8b #1:  (tty_files_lock){+.+.+.}, at:
> [<ffffffff9123e787>] selinux_bprm_committing_creds+0x55/0x22b CPU: 1 PID:
> 885 Comm: sulogin Not tainted 3.18.0-next-20141216 #30 Hardware name: Dell
> Inc. Latitude E6530/07Y85M, BIOS A15 06/20/2014 ffff880223744f10
> ffff88022410f9b8 ffffffff916ba529 0000000000000375 ffff880223744f10
> ffff88022410f9e8 ffffffff91063185 0000000000000006 0000000000000000
> 0000000000000000 0000000000000000 ffff88022410fa38 Call Trace:
>   [<ffffffff916ba529>] dump_stack+0x50/0xa8
>   [<ffffffff91063185>] ___might_sleep+0x1b6/0x1be
>   [<ffffffff910632a6>] __might_sleep+0x119/0x128
>   [<ffffffff91140720>] cache_alloc_debugcheck_before.isra.45+0x1d/0x1f
>   [<ffffffff91141d81>] kmem_cache_alloc+0x43/0x1c9
>   [<ffffffff914e148d>] __alloc_skb+0x42/0x1a3
>   [<ffffffff914e2b62>] skb_copy+0x3e/0xa3
>   [<ffffffff910c263e>] audit_log_end+0x83/0x100
>   [<ffffffff9123b8d3>] ? avc_audit_pre_callback+0x103/0x103
>   [<ffffffff91252a73>] common_lsm_audit+0x441/0x450
>   [<ffffffff9123c163>] slow_avc_audit+0x63/0x67
>   [<ffffffff9123c42c>] avc_has_perm+0xca/0xe3
>   [<ffffffff9123dc2d>] inode_has_perm+0x5a/0x65
>   [<ffffffff9123e7ca>] selinux_bprm_committing_creds+0x98/0x22b
>   [<ffffffff91239e64>] security_bprm_committing_creds+0xe/0x10
>   [<ffffffff911515e6>] install_exec_creds+0xe/0x79
>   [<ffffffff911974cf>] load_elf_binary+0xe36/0x10d7
>   [<ffffffff9115198e>] search_binary_handler+0x81/0x18c
>   [<ffffffff91153376>] do_execveat_common.isra.31+0x4e3/0x7b7
>   [<ffffffff91153669>] do_execve+0x1f/0x21
>   [<ffffffff91153967>] SyS_execve+0x25/0x29
>   [<ffffffff916c61a9>] stub_execve+0x69/0xa0
> 
> Cc: stable@xxxxxxxxxxxxxxx #v3.16-rc1
> Reported-by: Valdis Kletnieks <Valdis.Kletnieks@xxxxxx>
> Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> ---
>  kernel/audit.c |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)

Looks good to me, thanks.

I've got this patch (and the PID filter fix) queued up to go to Linus for 
v3.19; considering that -rc1 is due on Sunday I think I'll hold this until 
early next week (targeting -rc2) just in case something nasty appears after 
the merge window closes.

> diff --git a/kernel/audit.c b/kernel/audit.c
> index 7b83c55..ce484fb 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -429,7 +429,7 @@ static void kauditd_send_skb(struct sk_buff *skb)
>   * This function doesn't consume an skb as might be expected since it has
> to * copy it anyways.
>   */
> -static void kauditd_send_multicast_skb(struct sk_buff *skb)
> +static void kauditd_send_multicast_skb(struct sk_buff *skb, gfp_t gfp_mask)
> {
>  	struct sk_buff		*copy;
>  	struct audit_net	*aunet = net_generic(&init_net, audit_net_id);
> @@ -448,11 +448,11 @@ static void kauditd_send_multicast_skb(struct sk_buff
> *skb) * no reason for new multicast clients to continue with this
>  	 * non-compliance.
>  	 */
> -	copy = skb_copy(skb, GFP_KERNEL);
> +	copy = skb_copy(skb, gfp_mask);
>  	if (!copy)
>  		return;
> 
> -	nlmsg_multicast(sock, copy, 0, AUDIT_NLGRP_READLOG, GFP_KERNEL);
> +	nlmsg_multicast(sock, copy, 0, AUDIT_NLGRP_READLOG, gfp_mask);
>  }
> 
>  /*
> @@ -1949,7 +1949,7 @@ void audit_log_end(struct audit_buffer *ab)
>  		struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
> 
>  		nlh->nlmsg_len = ab->skb->len;
> -		kauditd_send_multicast_skb(ab->skb);
> +		kauditd_send_multicast_skb(ab->skb, ab->gfp_mask);
> 
>  		/*
>  		 * The original kaudit unicast socket sends up messages with

-- 
paul moore
security @ redhat

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