Commit 480db500 authored by Herbert Xu's avatar Herbert Xu
Browse files

crypto: hash - Fix test underflow in shash_ahash_digest 



The test on PAGE_SIZE - offset in shash_ahash_digest can underflow,
leading to execution of the fast path even if the data cannot be
mapped into a single page.

Fix this by splitting the test into four cases:

1) nbytes > sg->length: More than one SG entry, slow path.
2) !IS_ENABLED(CONFIG_HIGHMEM): fast path.
3) nbytes > (unsigned int)PAGE_SIZE - offset: Two highmem pages, slow path.
4) Highmem fast path.

Fixes: 5f7082ed ("crypto: hash - Export shash through hash")
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent da6f9bf4

crypto/ahash.c

+28 −16
Original line number Diff line number Diff line
@@ -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>
@@ -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;

	const u8 *data;

	int err;



	if (ahash_request_isvirt(req))

		return crypto_shash_digest(desc, req->svirt, nbytes,

					   req->result);

	data = req->svirt;

	if (!nbytes || ahash_request_isvirt(req))

		return crypto_shash_digest(desc, data, 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);



	page = sg_page(sg);

	offset = sg->offset;

	data = lowmem_page_address(page) + offset;

	if (!IS_ENABLED(CONFIG_HIGHMEM))

		return crypto_shash_digest(desc, data, nbytes, req->result);



		data = kmap_local_page(sg_page(sg));

	page += offset >> PAGE_SHIFT;

	offset = offset_in_page(offset);



	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);

	} else

		err = crypto_shash_init(desc) ?:

		      shash_ahash_finup(req, desc);



	return err;

}

EXPORT_SYMBOL_GPL(shash_ahash_digest);