linux-kernel - Re: [Linux-kernel-mentees] [PATCH v2 net] rose: Fix Null pointer dereference in rose_send

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Date:   Fri, 06 Nov 2020 13:04:27 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     Anmol Karn <anmol.karan123@...il.com>, ralf@...ux-mips.org,
        davem@...emloft.net, kuba@...nel.org
Cc:     gregkh@...uxfoundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hams@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzkaller-bugs@...glegroups.com,
        syzbot+a1c743815982d9496393@...kaller.appspotmail.com
Subject: Re: [Linux-kernel-mentees] [PATCH v2 net] rose: Fix Null pointer
 dereference in rose_send_frame()

On Thu, 2020-11-05 at 21:26 +0530, Anmol Karn wrote:
> rose_send_frame() dereferences `neigh->dev` when called from
> rose_transmit_clear_request(), and the first occurance of the `neigh`
> is in rose_loopback_timer() as `rose_loopback_neigh`, and it is
> initialized
> in rose_add_loopback_neigh() as NULL. i.e when `rose_loopback_neigh`
> used in 
> rose_loopback_timer() its `->dev` was still NULL and
> rose_loopback_timer() 
> was calling rose_rx_call_request() without checking for NULL.
> 
> - net/rose/rose_link.c
> This bug seems to get triggered in this line:
> 
> rose_call = (ax25_address *)neigh->dev->dev_addr;
> 
> Fix it by adding NULL checking for `rose_loopback_neigh->dev` in
> rose_loopback_timer(). 
> 
> Reported-and-tested-by: 
> syzbot+a1c743815982d9496393@...kaller.appspotmail.com 
> Link: 
> https://syzkaller.appspot.com/bug?id=9d2a7ca8c7f2e4b682c97578dfa3f236258300b3
>  
> Signed-off-by: Anmol Karn <anmol.karan123@...il.com>

missing proper fixes tag.

> ---
>  net/rose/rose_loopback.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c
> index 7b094275ea8b..cd7774cb1d07 100644
> --- a/net/rose/rose_loopback.c
> +++ b/net/rose/rose_loopback.c
> @@ -96,7 +96,7 @@ static void rose_loopback_timer(struct timer_list
> *unused)
>  		}
>  
>  		if (frametype == ROSE_CALL_REQUEST) {
> -			if ((dev = rose_dev_get(dest)) != NULL) {
> +			if (rose_loopback_neigh->dev && (dev =
> rose_dev_get(dest)) != NULL) {
>  				if (rose_rx_call_request(skb, dev,
> rose_loopback_neigh, lci_o) == 0)
>  					kfree_skb(skb);
>  			} else {

check patch is not happy:

WARNING:TYPO_SPELLING: 'occurance' may be misspelled - perhaps
'occurrence'?
#7: 
rose_transmit_clear_request(), and the first occurance of the `neigh`

ERROR:ASSIGN_IN_IF: do not use assignment in if condition
#36: FILE: net/rose/rose_loopback.c:99:
+                       if (rose_loopback_neigh->dev && (dev =
rose_dev_get(dest)) != NULL) {

total: 1 errors, 1 warnings, 0 checks, 8 lines checked