Subject: Re: [PATCH net] netconsole: avoid OOB reads, msg is not nul-terminated

From: Breno Leitao <[email-masked]>
Date: Mon, 2 Mar 2026 01:47:18 -0800

On Sun, Feb 22, 2026 at 04:13:19PM +0000, Simon Horman wrote:
> On Thu, Feb 19, 2026 at 11:50:21AM -0800, Jakub Kicinski wrote:
> > msg passed to netconsole from the console subsystem is not guaranteed
> > to be nul-terminated. Before recent
> > commit 7eab73b18630 ("netconsole: convert to NBCON console infrastructure")
> > the message would be placed in printk_shared_pbufs, a static global
> > buffer, so KASAN had harder time catching OOB accesses. Now we see:
> > 
> >     printk: console [netcon_ext0] enabled
> >     BUG: KASAN: slab-out-of-bounds in string+0x1f7/0x240
> >     Read of size 1 at addr ffff88813b6d4c00 by task pr/netcon_ext0/594
> > 
> >     CPU: 65 UID: 0 PID: 594 Comm: pr/netcon_ext0 Not tainted 6.19.0-11754-g4246fd6547c9
> >     Call Trace:
> >      kasan_report+0xe4/0x120
> >      string+0x1f7/0x240
> >      vsnprintf+0x655/0xba0
> >      scnprintf+0xba/0x120
> >      netconsole_write+0x3fe/0xa10
> >      nbcon_emit_next_record+0x46e/0x860
> >      nbcon_kthread_func+0x623/0x750
> > 
> >     Allocated by task 1:
> >      nbcon_alloc+0x1ea/0x450
> >      register_console+0x26b/0xe10
> >      init_netconsole+0xbb0/0xda0
> > 
> >     The buggy address belongs to the object at ffff88813b6d4000
> >                 which belongs to the cache kmalloc-4k of size 4096
> >     The buggy address is located 0 bytes to the right of
> >                 allocated 3072-byte region [ffff88813b6d4000, ffff88813b6d4c00)
> > 
> > Fixes: c62c0a17f9b7 ("netconsole: Append kernel version to message")
> > Signed-off-by: Jakub Kicinski <[email-masked]>
> 
> Reviewed-by: Simon Horman <[email-masked]>

Thanks for the fix and review while I was out.

--breno