diff mbox series

lib/mpi: Fix buffer overrun when SG is too long

Message ID Y6FjQPZiJYTEG1zI@gondor.apana.org.au
State New
Headers
Series lib/mpi: Fix buffer overrun when SG is too long |

Commit Message

Herbert Xu Dec. 20, 2022, 7:24 a.m. UTC 
  On Mon, Dec 19, 2022 at 09:49:29AM +0100, Roberto Sassu wrote:
>
> do you have any news on this bug?

Thanks for the reminder.  Could you please try this patch?

---8<---
The helper mpi_read_raw_from_sgl ignores the second parameter
nbytes when reading the SG list and may overrun its own buffer
because it only allocates enough memory according to nbytes.

Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers")
Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Comments

Roberto Sassu Dec. 20, 2022, 10:36 a.m. UTC | #1 
On 12/20/2022 8:24 AM, Herbert Xu wrote:
> On Mon, Dec 19, 2022 at 09:49:29AM +0100, Roberto Sassu wrote:
>>
>> do you have any news on this bug?
> 
> Thanks for the reminder.  Could you please try this patch?

Tried, could not boot the UML kernel.

After looking, it seems we have to call sg_miter_stop(). Or 
alternatively, we could let sg_miter_next() be called but not writing 
anything inside the loop.

With either of those fixes, the tests pass (using one scatterlist).

Roberto

> ---8<---
> The helper mpi_read_raw_from_sgl ignores the second parameter
> nbytes when reading the SG list and may overrun its own buffer
> because it only allocates enough memory according to nbytes.
> 
> Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers")
> Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> 
> diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
> index 39c4c6731094..6bffc68c1a5a 100644
> --- a/lib/mpi/mpicoder.c
> +++ b/lib/mpi/mpicoder.c
> @@ -494,17 +494,15 @@ MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
>   	val->sign = 0;
>   	val->nlimbs = nlimbs;
>   
> -	if (nbytes == 0)
> -		return val;
> -
>   	j = nlimbs - 1;
>   	a = 0;
>   	z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
>   	z %= BYTES_PER_MPI_LIMB;
>   
> -	while (sg_miter_next(&miter)) {
> +	while (nbytes && sg_miter_next(&miter)) {
>   		buff = miter.addr;
> -		len = miter.length;
> +		len = min_t(unsigned, miter.length, nbytes);
> +		nbytes -= len;
>   
>   		for (x = 0; x < len; x++) {
>   			a <<= 8;
Eric Biggers Dec. 20, 2022, 8:30 p.m. UTC | #2 
On Tue, Dec 20, 2022 at 11:36:50AM +0100, Roberto Sassu wrote:
> On 12/20/2022 8:24 AM, Herbert Xu wrote:
> > On Mon, Dec 19, 2022 at 09:49:29AM +0100, Roberto Sassu wrote:
> > > 
> > > do you have any news on this bug?
> > 
> > Thanks for the reminder.  Could you please try this patch?
> 
> Tried, could not boot the UML kernel.
> 
> After looking, it seems we have to call sg_miter_stop(). Or alternatively,
> we could let sg_miter_next() be called but not writing anything inside the
> loop.
> 
> With either of those fixes, the tests pass (using one scatterlist).
> 
> Roberto
> 
> > ---8<---
> > The helper mpi_read_raw_from_sgl ignores the second parameter
> > nbytes when reading the SG list and may overrun its own buffer
> > because it only allocates enough memory according to nbytes.
> > 
> > Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers")
> > Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com>
> > Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> > 
> > diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
> > index 39c4c6731094..6bffc68c1a5a 100644
> > --- a/lib/mpi/mpicoder.c
> > +++ b/lib/mpi/mpicoder.c
> > @@ -494,17 +494,15 @@ MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
> >   	val->sign = 0;
> >   	val->nlimbs = nlimbs;
> > -	if (nbytes == 0)
> > -		return val;
> > -
> >   	j = nlimbs - 1;
> >   	a = 0;
> >   	z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
> >   	z %= BYTES_PER_MPI_LIMB;
> > -	while (sg_miter_next(&miter)) {
> > +	while (nbytes && sg_miter_next(&miter)) {
> >   		buff = miter.addr;
> > -		len = miter.length;
> > +		len = min_t(unsigned, miter.length, nbytes);
> > +		nbytes -= len;
> >   		for (x = 0; x < len; x++) {
> >   			a <<= 8;

I think it should look like:

	while (nbytes) {
		sg_miter_next(&miter);
		...
	}
	sg_miter_stop(&miter);

- Eric
diff mbox series

Patch

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index 39c4c6731094..6bffc68c1a5a 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -494,17 +494,15 @@  MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 	val->sign = 0;
 	val->nlimbs = nlimbs;
 
-	if (nbytes == 0)
-		return val;
-
 	j = nlimbs - 1;
 	a = 0;
 	z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 	z %= BYTES_PER_MPI_LIMB;
 
-	while (sg_miter_next(&miter)) {
+	while (nbytes && sg_miter_next(&miter)) {
 		buff = miter.addr;
-		len = miter.length;
+		len = min_t(unsigned, miter.length, nbytes);
+		nbytes -= len;
 
 		for (x = 0; x < len; x++) {
 			a <<= 8;