Commit 439bea10 authored by Eric Biggers's avatar Eric Biggers
Browse files

fs-verity: use mempool for hash requests 

When initializing an fs-verity hash algorithm, also initialize a mempool
that contains a single preallocated hash request object.  Then replace
the direct calls to ahash_request_alloc() and ahash_request_free() with
allocating and freeing from this mempool.

This eliminates the possibility of the allocation failing, which is
desirable for the I/O path.

This doesn't cause deadlocks because there's no case where multiple hash
requests are needed at a time to make forward progress.

Link: https://lore.kernel.org/r/20191231175545.20709-1-ebiggers@kernel.org


Reviewed-by: default avatarTheodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
parent fd39073d

fs/verity/enable.c

+5 −3
Original line number Diff line number Diff line
@@ -165,9 +165,11 @@ static int build_merkle_tree(struct file *filp, 
		return 0;

	}



	/* This allocation never fails, since it's mempool-backed. */

	req = fsverity_alloc_hash_request(params->hash_alg, GFP_KERNEL);



	pending_hashes = kmalloc(params->block_size, GFP_KERNEL);

	req = ahash_request_alloc(params->hash_alg->tfm, GFP_KERNEL);

	if (!pending_hashes || !req)

	if (!pending_hashes)

		goto out;



	/*
@@ -189,7 +191,7 @@ static int build_merkle_tree(struct file *filp, 
	err = 0;

out:

	kfree(pending_hashes);

	ahash_request_free(req);

	fsverity_free_hash_request(params->hash_alg, req);

	return err;

}

fs/verity/fsverity_private.h

+11 −5
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 


#include <crypto/sha.h>

#include <linux/fsverity.h>

#include <linux/mempool.h>



struct ahash_request;
@@ -37,11 +38,12 @@ struct fsverity_hash_alg { 
	const char *name;	  /* crypto API name, e.g. sha256 */

	unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */

	unsigned int block_size;  /* block size in bytes, e.g. 64 for SHA-256 */

	mempool_t req_pool;	  /* mempool with a preallocated hash request */

};



/* Merkle tree parameters: hash algorithm, initial hash state, and topology */

struct merkle_tree_params {

	const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */

	struct fsverity_hash_alg *hash_alg; /* the hash algorithm */

	const u8 *hashstate;		/* initial hash state or NULL */

	unsigned int digest_size;	/* same as hash_alg->digest_size */

	unsigned int block_size;	/* size of data and tree blocks */
@@ -115,14 +117,18 @@ struct fsverity_signed_digest { 


extern struct fsverity_hash_alg fsverity_hash_algs[];



const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,

struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,

						unsigned int num);

const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,

struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,

						  gfp_t gfp_flags);

void fsverity_free_hash_request(struct fsverity_hash_alg *alg,

				struct ahash_request *req);

const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,

				      const u8 *salt, size_t salt_size);

int fsverity_hash_page(const struct merkle_tree_params *params,

		       const struct inode *inode,

		       struct ahash_request *req, struct page *page, u8 *out);

int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,

int fsverity_hash_buffer(struct fsverity_hash_alg *alg,

			 const void *data, size_t size, u8 *out);

void __init fsverity_check_hash_algs(void);

fs/verity/hash_algs.c

+73 −25
Original line number Diff line number Diff line
@@ -24,6 +24,8 @@ struct fsverity_hash_alg fsverity_hash_algs[] = { 
	},

};



static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);



/**

 * fsverity_get_hash_alg() - validate and prepare a hash algorithm

 * @inode: optional inode for logging purposes
@@ -36,7 +38,7 @@ struct fsverity_hash_alg fsverity_hash_algs[] = { 
 *

 * Return: pointer to the hash alg on success, else an ERR_PTR()

 */

const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,

struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,

						unsigned int num)

{

	struct fsverity_hash_alg *alg;
@@ -50,10 +52,15 @@ const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 
	}

	alg = &fsverity_hash_algs[num];



	/* pairs with cmpxchg() below */

	tfm = READ_ONCE(alg->tfm);

	if (likely(tfm != NULL))

	/* pairs with smp_store_release() below */

	if (likely(smp_load_acquire(&alg->tfm) != NULL))

		return alg;



	mutex_lock(&fsverity_hash_alg_init_mutex);



	if (alg->tfm != NULL)

		goto out_unlock;



	/*

	 * Using the shash API would make things a bit simpler, but the ahash

	 * API is preferable as it allows the use of crypto accelerators.
@@ -64,12 +71,14 @@ const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 
			fsverity_warn(inode,

				      "Missing crypto API support for hash algorithm \"%s\"",

				      alg->name);

			return ERR_PTR(-ENOPKG);

			alg = ERR_PTR(-ENOPKG);

			goto out_unlock;

		}

		fsverity_err(inode,

			     "Error allocating hash algorithm \"%s\": %ld",

			     alg->name, PTR_ERR(tfm));

		return ERR_CAST(tfm);

		alg = ERR_CAST(tfm);

		goto out_unlock;

	}



	err = -EINVAL;
@@ -78,18 +87,61 @@ const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 
	if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm)))

		goto err_free_tfm;



	err = mempool_init_kmalloc_pool(&alg->req_pool, 1,

					sizeof(struct ahash_request) +

					crypto_ahash_reqsize(tfm));

	if (err)

		goto err_free_tfm;



	pr_info("%s using implementation \"%s\"\n",

		alg->name, crypto_ahash_driver_name(tfm));



	/* pairs with READ_ONCE() above */

	if (cmpxchg(&alg->tfm, NULL, tfm) != NULL)

		crypto_free_ahash(tfm);



	return alg;

	/* pairs with smp_load_acquire() above */

	smp_store_release(&alg->tfm, tfm);

	goto out_unlock;



err_free_tfm:

	crypto_free_ahash(tfm);

	return ERR_PTR(err);

	alg = ERR_PTR(err);

out_unlock:

	mutex_unlock(&fsverity_hash_alg_init_mutex);

	return alg;

}



/**

 * fsverity_alloc_hash_request() - allocate a hash request object

 * @alg: the hash algorithm for which to allocate the request

 * @gfp_flags: memory allocation flags

 *

 * This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in

 * @gfp_flags.  However, in that case this might need to wait for all

 * previously-allocated requests to be freed.  So to avoid deadlocks, callers

 * must never need multiple requests at a time to make forward progress.

 *

 * Return: the request object on success; NULL on failure (but see above)

 */

struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,

						  gfp_t gfp_flags)

{

	struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags);



	if (req)

		ahash_request_set_tfm(req, alg->tfm);

	return req;

}



/**

 * fsverity_free_hash_request() - free a hash request object

 * @alg: the hash algorithm

 * @req: the hash request object to free

 */

void fsverity_free_hash_request(struct fsverity_hash_alg *alg,

				struct ahash_request *req)

{

	if (req) {

		ahash_request_zero(req);

		mempool_free(req, &alg->req_pool);

	}

}



/**
@@ -101,7 +153,7 @@ err_free_tfm: 
 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed

 *	   initial hash state on success or an ERR_PTR() on failure.

 */

const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,

const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,

				      const u8 *salt, size_t salt_size)

{

	u8 *hashstate = NULL;
@@ -119,11 +171,8 @@ const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg, 
	if (!hashstate)

		return ERR_PTR(-ENOMEM);



	req = ahash_request_alloc(alg->tfm, GFP_KERNEL);

	if (!req) {

		err = -ENOMEM;

		goto err_free;

	}

	/* This allocation never fails, since it's mempool-backed. */

	req = fsverity_alloc_hash_request(alg, GFP_KERNEL);



	/*

	 * Zero-pad the salt to the next multiple of the input size of the hash
@@ -158,7 +207,7 @@ const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg, 
	if (err)

		goto err_free;

out:

	ahash_request_free(req);

	fsverity_free_hash_request(alg, req);

	kfree(padded_salt);

	return hashstate;
@@ -229,7 +278,7 @@ int fsverity_hash_page(const struct merkle_tree_params *params, 
 *

 * Return: 0 on success, -errno on failure

 */

int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,

int fsverity_hash_buffer(struct fsverity_hash_alg *alg,

			 const void *data, size_t size, u8 *out)

{

	struct ahash_request *req;
@@ -237,9 +286,8 @@ int fsverity_hash_buffer(const struct fsverity_hash_alg *alg, 
	DECLARE_CRYPTO_WAIT(wait);

	int err;



	req = ahash_request_alloc(alg->tfm, GFP_KERNEL);

	if (!req)

		return -ENOMEM;

	/* This allocation never fails, since it's mempool-backed. */

	req = fsverity_alloc_hash_request(alg, GFP_KERNEL);



	sg_init_one(&sg, data, size);

	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
@@ -249,7 +297,7 @@ int fsverity_hash_buffer(const struct fsverity_hash_alg *alg, 


	err = crypto_wait_req(crypto_ahash_digest(req), &wait);



	ahash_request_free(req);

	fsverity_free_hash_request(alg, req);

	return err;

}

fs/verity/open.c

+2 −2
Original line number Diff line number Diff line
@@ -31,7 +31,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, 
				     unsigned int log_blocksize,

				     const u8 *salt, size_t salt_size)

{

	const struct fsverity_hash_alg *hash_alg;

	struct fsverity_hash_alg *hash_alg;

	int err;

	u64 blocks;

	u64 offset;
@@ -127,7 +127,7 @@ out_err: 
 * Compute the file measurement by hashing the fsverity_descriptor excluding the

 * signature and with the sig_size field set to 0.

 */

static int compute_file_measurement(const struct fsverity_hash_alg *hash_alg,

static int compute_file_measurement(struct fsverity_hash_alg *hash_alg,

				    struct fsverity_descriptor *desc,

				    u8 *measurement)

{

fs/verity/verify.c

+6 −11
Original line number Diff line number Diff line
@@ -192,13 +192,12 @@ bool fsverity_verify_page(struct page *page) 
	struct ahash_request *req;

	bool valid;



	req = ahash_request_alloc(vi->tree_params.hash_alg->tfm, GFP_NOFS);

	if (unlikely(!req))

		return false;

	/* This allocation never fails, since it's mempool-backed. */

	req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);



	valid = verify_page(inode, vi, req, page, 0);



	ahash_request_free(req);

	fsverity_free_hash_request(vi->tree_params.hash_alg, req);



	return valid;

}
@@ -229,12 +228,8 @@ void fsverity_verify_bio(struct bio *bio) 
	struct bvec_iter_all iter_all;

	unsigned long max_ra_pages = 0;



	req = ahash_request_alloc(params->hash_alg->tfm, GFP_NOFS);

	if (unlikely(!req)) {

		bio_for_each_segment_all(bv, bio, iter_all)

			SetPageError(bv->bv_page);

		return;

	}

	/* This allocation never fails, since it's mempool-backed. */

	req = fsverity_alloc_hash_request(params->hash_alg, GFP_NOFS);



	if (bio->bi_opf & REQ_RAHEAD) {

		/*
@@ -262,7 +257,7 @@ void fsverity_verify_bio(struct bio *bio) 
			SetPageError(page);

	}



	ahash_request_free(req);

	fsverity_free_hash_request(params->hash_alg, req);

}

EXPORT_SYMBOL_GPL(fsverity_verify_bio);

#endif /* CONFIG_BLOCK */

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