[apparmor] [PATCH] apparmor: Use shash crypto API interface for profile hashes

[Tyler Hicks]

Use the shash interface, rather than the hash interface, when hashing
AppArmor profiles. The shash interface does not use scatterlists and it
is a better fit for what AppArmor needs.

This fixes a kernel paging BUG when aa_calc_profile_hash() is passed a
buffer from vmalloc(). The hash interface requires callers to handle
vmalloc() buffers differently than what AppArmor was doing. Due to
vmalloc() memory not being physically contiguous, each individual page
behind the buffer must be assigned to a scatterlist with sg_set_page()
and then the scatterlist passed to crypto_hash_update().

The shash interface does not have that limitation and allows vmalloc()
and kmalloc() buffers to be handled in the same manner.

https://launchpad.net/bugs/1216294/

Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
Cc: John Johansen <john.johansen at canonical.com>
---

I've tested this patch by comparing aafs/policy/profiles/*/sha1 between a
patched i386 VM (i386 is where the BUG is easily reproduced) and an unpatched
amd64 VM. Then I did `service apparmor restart` to trigger a profile
replacement and compared the sha1 files in aafs again. I put all of that into a
loop and let it run for a while.

Tyler

 security/apparmor/crypto.c | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

diff --git a/security/apparmor/crypto.c b/security/apparmor/crypto.c
index d6222ba..532471d 100644
--- a/security/apparmor/crypto.c
+++ b/security/apparmor/crypto.c
@@ -15,14 +15,14 @@
  * it should be.
  */
 
-#include <linux/crypto.h>
+#include <crypto/hash.h>
 
 #include "include/apparmor.h"
 #include "include/crypto.h"
 
 static unsigned int apparmor_hash_size;
 
-static struct crypto_hash *apparmor_tfm;
+static struct crypto_shash *apparmor_tfm;
 
 unsigned int aa_hash_size(void)
 {
@@ -32,35 +32,33 @@ unsigned int aa_hash_size(void)
 int aa_calc_profile_hash(struct aa_profile *profile, u32 version, void *start,
 			 size_t len)
 {
-	struct scatterlist sg[2];
-	struct hash_desc desc = {
-		.tfm = apparmor_tfm,
-		.flags = 0
-	};
+	struct {
+		struct shash_desc shash;
+		char ctx[crypto_shash_descsize(apparmor_tfm)];
+	} desc;
 	int error = -ENOMEM;
 	u32 le32_version = cpu_to_le32(version);
 
 	if (!apparmor_tfm)
 		return 0;
 
-	sg_init_table(sg, 2);
-	sg_set_buf(&sg[0], &le32_version, 4);
-	sg_set_buf(&sg[1], (u8 *) start, len);
-
 	profile->hash = kzalloc(apparmor_hash_size, GFP_KERNEL);
 	if (!profile->hash)
 		goto fail;
 
-	error = crypto_hash_init(&desc);
+	desc.shash.tfm = apparmor_tfm;
+	desc.shash.flags = 0;
+
+	error = crypto_shash_init(&desc.shash);
 	if (error)
 		goto fail;
-	error = crypto_hash_update(&desc, &sg[0], 4);
+	error = crypto_shash_update(&desc.shash, (u8 *) &le32_version, 4);
 	if (error)
 		goto fail;
-	error = crypto_hash_update(&desc, &sg[1], len);
+	error = crypto_shash_update(&desc.shash, (u8 *) start, len);
 	if (error)
 		goto fail;
-	error = crypto_hash_final(&desc, profile->hash);
+	error = crypto_shash_final(&desc.shash, profile->hash);
 	if (error)
 		goto fail;
 
@@ -75,19 +73,19 @@ fail:
 
 static int __init init_profile_hash(void)
 {
-	struct crypto_hash *tfm;
+	struct crypto_shash *tfm;
 
 	if (!apparmor_initialized)
 		return 0;
 
-	tfm = crypto_alloc_hash("sha1", 0, CRYPTO_ALG_ASYNC);
+	tfm = crypto_alloc_shash("sha1", 0, CRYPTO_ALG_ASYNC);
 	if (IS_ERR(tfm)) {
 		int error = PTR_ERR(tfm);
 		AA_ERROR("failed to setup profile sha1 hashing: %d\n", error);
 		return error;
 	}
 	apparmor_tfm = tfm;
-	apparmor_hash_size = crypto_hash_digestsize(apparmor_tfm);
+	apparmor_hash_size = crypto_shash_digestsize(apparmor_tfm);
 
 	aa_info_message("AppArmor sha1 policy hashing enabled");
 
-- 
1.8.3.2