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'
- Eric
