| Message ID | Y6Kthn+rIUnCEJWz@gondor.apana.org.au (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | [v2] lib/mpi: Fix buffer overrun when SG is too long | expand |
On Wed, Dec 21, 2022 at 02:53:58PM +0800, Herbert Xu wrote: > 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 <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..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; That's fine, I guess. One quirk of the above approach is that if the last needed element of the scatterlist has a lot of extra pages, this will iterate through all those extra pages, processing 0 bytes from each. It could just stop when done. I suppose it's not worth worrying about that case, though. - Eric
On Wed, Dec 21, 2022 at 12:53:29PM -0800, Eric Biggers wrote: > > That's fine, I guess. One quirk of the above approach is that if the last > needed element of the scatterlist has a lot of extra pages, this will iterate > through all those extra pages, processing 0 bytes from each. It could just stop > when done. I suppose it's not worth worrying about that case, though. Ideally this should be handled in the sg_miter interface, IOW, it should allow us to cap the SG list at a certain number of bytes as opposed to a certain number of entries. Cheers,
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;