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 <[email protected]>
> > Signed-off-by: Herbert Xu <[email protected]>
> >
> > 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
On Tue, Dec 20, 2022 at 08:30:16PM +0000, Eric Biggers wrote:
>
> > 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).
Thanks for the quick feedback Roberto!
> I think it should look like:
>
> while (nbytes) {
> sg_miter_next(&miter);
> ...
> }
> sg_miter_stop(&miter);
You're right Eric. However, we could also do it by simply not
checking nbytes since we already set nents according to nbytes
at the top of the function.
---8<---
The helper mpi_read_raw_from_sgl sets the number of entries in
the SG list according to nbytes. However, if the last entry
in the SG list contains more data than nbytes, then it may overrun
the buffer because it only allocates enough memory for nbytes.
Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers")
Reported-by: Roberto Sassu <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>
diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index 39c4c6731094..157ef532a6a2 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -504,7 +501,8 @@ MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
while (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;
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt