Re: [PATCH] drivers: net: bsd_comp: fix integer overflow in bsd_decompress()

[Sergey Shtylyov <s.shtylyov@omp.ru>]

Hello!

   Failed to notice an issue with the subject in the internal review;
I think it should look like "net: ppp: bsd_comp: fix integer overflow
in bsd_decompress()"...

On 8/12/24 11:43 AM, Roman Smirnov wrote:

> The result of a bit shift has type int.

   So far, so good... :-)

> If ibuf is greater than or

   *ibuf maybe? :-)

> equal to 128, a sign switch will occur.

   I wonder whether you had looked at the .lsy file before writing
that...
   Actually, movzvl (%rdi),%eax is used when reading *buf, so no 
sign extension occurs at this point... it occurs when casting the 
result of shift to *unsignjed long*

> After that, the higher 32 bits in accm will be set to 1.

   Only if we have 1 in the bit 31 after shl %cl,%eax...

> Cast the result of the expression to unsigned long.

   I strongly suspect we should re-declare accm as *unsigned int*
instead...

> Found by Linux Verification Center (linuxtesting.org) with Svace.
> 
> Signed-off-by: Roman Smirnov <r.smirnov@omp.ru>
> ---
>  drivers/net/ppp/bsd_comp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ppp/bsd_comp.c b/drivers/net/ppp/bsd_comp.c
> index 55954594e157..078fe8c9bee8 100644
> --- a/drivers/net/ppp/bsd_comp.c
> +++ b/drivers/net/ppp/bsd_comp.c
> @@ -918,7 +918,7 @@ static int bsd_decompress (void *state, unsigned char *ibuf, int isize,
>  	 */
>  
>  	bitno -= 8;
> -	accm  |= *ibuf++ << bitno;
> +	accm  |= (unsigned long)(*ibuf++) << bitno;
>  	if (tgtbitno < bitno)
>  	  {
>  	    continue;
> 

MBR, Sergey