linux-kernel - Re: [PATCH v2] net: caif: fix memory leak in ldisc

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Message-ID: <ed294369-e463-4d4b-83c8-43df0e24c014@kernel.org>
Date: Mon, 19 Jan 2026 08:00:37 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Osama Abdelkader <osama.abdelkader@...il.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Sjur Braendeland <sjur.brandeland@...ricsson.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: syzbot+f9d847b2b84164fa69f3@...kaller.appspotmail.com,
 stable@...r.kernel.org
Subject: Re: [PATCH v2] net: caif: fix memory leak in ldisc_receive

On 19. 01. 26, 7:58, Jiri Slaby wrote:
> On 18. 01. 26, 18:44, Osama Abdelkader wrote:
>> Add NULL pointer checks for ser and ser->dev in ldisc_receive() to
>> prevent memory leaks when the function is called during device close
>> or in race conditions where tty->disc_data or ser->dev may be NULL.
>>
>> The memory leak occurred because ser->dev was accessed before checking
>> if ser or ser->dev was NULL, which could cause a NULL pointer
>> dereference or use of freed memory. Additionally, set tty->disc_data
>> to NULL in ldisc_close() to prevent receive_buf() from using a freed
>> ser pointer after the line discipline is closed.
>>
>> Reported-by: syzbot+f9d847b2b84164fa69f3@...kaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=f9d847b2b84164fa69f3
>> Fixes: 9b27105b4a44 ("net-caif-driver: add CAIF serial driver (ldisc)")
>> CC: stable@...r.kernel.org
>> Signed-off-by: Osama Abdelkader <osama.abdelkader@...il.com>
>> ---
>> v2:
>> 1.Combine NULL pointer checks for ser and ser->dev in ldisc_receive()
>> 2.Set tty->disc_data = NULL in ldisc_close() to prevent receive_buf()
>> from using a freed ser pointer after close.
>> 3.Add NULL pointer check for ser in ldisc_close()
>> ---
>>   drivers/net/caif/caif_serial.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/ 
>> caif_serial.c
>> index c398ac42eae9..970237a3ccca 100644
>> --- a/drivers/net/caif/caif_serial.c
>> +++ b/drivers/net/caif/caif_serial.c
>> @@ -152,6 +152,8 @@ static void ldisc_receive(struct tty_struct *tty, 
>> const u8 *data,
>>       int ret;
>>       ser = tty->disc_data;
>> +    if (!ser || !ser->dev)
>> +        return;
>>       /*
>>        * NOTE: flags may contain information about break or overrun.
>> @@ -170,8 +172,6 @@ static void ldisc_receive(struct tty_struct *tty, 
>> const u8 *data,
>>           return;
>>       }
>> -    BUG_ON(ser->dev == NULL);
>> -
>>       /* Get a suitable caif packet and copy in data. */
>>       skb = netdev_alloc_skb(ser->dev, count+1);
> 
> Wait, the reported error is memory leak of mem allocated here. So both 
> ser and ser->dev appear to be valid?
> 
> So instead, does netif_rx() return an error few lines below for some 
> reason? So should skb just be freed in that path?
> 
>          if (skb == NULL)
>                  return;
>          skb_put_data(skb, data, count);
> 
>          skb->protocol = htons(ETH_P_CAIF);
>          skb_reset_mac_header(skb);
>          debugfs_rx(ser, data, count);
>          /* Push received packet up the stack. */
>          ret = netif_rx(skb);
>          if (!ret) {
>                  ser->dev->stats.rx_packets++;
>                  ser->dev->stats.rx_bytes += count;
>          } else
>                  ++ser->dev->stats.rx_dropped;
> 
> Not calling skb_free() in this else path _is_ a BUG™ in any case IMO.

No, it's not: netif_rx() always eats the buffer. So care to elaborate 
why the socket buffer is actually leaked?

> thanks,
-- 
js
suse labs