Re: [PATCH 6.12] netconsole: avoid OOB reads, msg is not nul-terminated

[Breno Leitao]

On Mon, Aug 03, 2026 at 08:41:29PM +0200, Markus Boehme wrote:
> From: Jakub Kicinski <kuba@xxxxxxxxxx>
> 
> [ Upstream commit 82aec772fca2223bc5774bd9af486fd95766e578 ]
> 
> 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 <kuba@xxxxxxxxxx>
> Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
> Link: https://patch.msgid.link/20260219195021.2099699-1-kuba@xxxxxxxxxx
> Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>

Acked-by: Breno Leitao <leitao@xxxxxxxxxx>