On Tue, Mar 11, 2025 at 10:44:31AM -0700, Eric Biggers wrote:
> On Tue, Mar 11, 2025 at 06:20:31PM +0800, Herbert Xu wrote:
> > Use nth_page instead of adding n to the page pointer.
> >
> > This also fixes a real bug in shash_ahash_digest where the the
> > check for continguous hash data may be incorrect in the presence
> > of highmem. This could result in an incorrect hash or worse.
> >
> > Fixes: 5f7082ed4f48 ("crypto: hash - Export shash through hash")
> > Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> > ---
> > crypto/ahash.c | 38 +++++++++++++++++++++++++-------------
> > 1 file changed, 25 insertions(+), 13 deletions(-)
> >
> > diff --git a/crypto/ahash.c b/crypto/ahash.c
> > index 9c26175c21a8..75d642897e36 100644
> > --- a/crypto/ahash.c
> > +++ b/crypto/ahash.c
> > @@ -16,6 +16,7 @@
> > #include <linux/cryptouser.h>
> > #include <linux/err.h>
> > #include <linux/kernel.h>
> > +#include <linux/mm.h>
> > #include <linux/module.h>
> > #include <linux/sched.h>
> > #include <linux/slab.h>
> > @@ -79,7 +80,7 @@ static int hash_walk_new_entry(struct crypto_hash_walk *walk)
> >
> > sg = walk->sg;
> > walk->offset = sg->offset;
> > - walk->pg = sg_page(walk->sg) + (walk->offset >> PAGE_SHIFT);
> > + walk->pg = nth_page(sg_page(walk->sg), walk->offset >> PAGE_SHIFT);
> > walk->offset = offset_in_page(walk->offset);
> > walk->entrylen = sg->length;
> >
> > @@ -201,25 +202,36 @@ int shash_ahash_digest(struct ahash_request *req, struct shash_desc *desc)
> > unsigned int nbytes = req->nbytes;
> > struct scatterlist *sg;
> > unsigned int offset;
> > + struct page *page;
> > + void *data;
> > int err;
> >
> > - if (ahash_request_isvirt(req))
> > + if (!nbytes || ahash_request_isvirt(req))
> > return crypto_shash_digest(desc, req->svirt, nbytes,
> > req->result);
> >
> > - if (nbytes &&
> > - (sg = req->src, offset = sg->offset,
> > - nbytes <= min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset))) {
> > - void *data;
> > + sg = req->src;
> > + if (nbytes > sg->length)
> > + return crypto_shash_init(desc) ?:
> > + shash_ahash_finup(req, desc);
> >
> > - data = kmap_local_page(sg_page(sg));
> > - err = crypto_shash_digest(desc, data + offset, nbytes,
> > - req->result);
> > - kunmap_local(data);
> > - } else
> > - err = crypto_shash_init(desc) ?:
> > - shash_ahash_finup(req, desc);
> > + page = sg_page(sg);
> > + offset = sg->offset;
> > + page = nth_page(page, offset >> PAGE_SHIFT);
> > + offset = offset_in_page(offset);
> >
> > + if (!IS_ENABLED(CONFIG_HIGHMEM))
> > + return crypto_shash_digest(desc, page_address(page) + offset,
> > + nbytes, req->result);
> > +
> > + if (nbytes > (unsigned int)PAGE_SIZE - offset)
> > + return crypto_shash_init(desc) ?:
> > + shash_ahash_finup(req, desc);
> > +
> > + data = kmap_local_page(page);
> > + err = crypto_shash_digest(desc, data + offset, nbytes,
> > + req->result);
> > + kunmap_local(data);
> > return err;
>
> I guess you think this is fixing a bug in the case where sg->offset > PAGE_SIZE?
> Is that case even supported? It is supposed to be the offset into a page.
>
> Even if so, a simpler fix (1 line) would be to use:
> 'sg->length >= nbytes && sg->offset + nbytes <= PAGE_SIZE'
Or just make this optimization specific to !HIGHMEM, and use
nbytes <= sg->length and sg_virt().
- Eric
