[ 30/48] dm crypt: fix access beyond the end of allocated space

From: Willy Tarreau
Date: Sun Nov 16 2014 - 17:01:12 EST

2.6.32-longterm review patch. If anyone has any objections, please let me know.


From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

commit d49ec52ff6ddcda178fc2476a109cf1bd1fa19ed upstream

The DM crypt target accesses memory beyond allocated space resulting in
a crash on 32 bit x86 systems.

This bug is very old (it dates back to 2.6.25 commit 3a7f6c990ad04 "dm
crypt: use async crypto"). However, this bug was masked by the fact
that kmalloc rounds the size up to the next power of two. This bug
wasn't exposed until 3.17-rc1 commit 298a9fa08a ("dm crypt: use per-bio
data"). By switching to using per-bio data there was no longer any
padding beyond the end of a dm-crypt allocated memory block.

To minimize allocation overhead dm-crypt puts several structures into one
block allocated with kmalloc. The block holds struct ablkcipher_request,
cipher-specific scratch pad (crypto_ablkcipher_reqsize(any_tfm(cc))),
struct dm_crypt_request and an initialization vector.

The variable dmreq_start is set to offset of struct dm_crypt_request
within this memory block. dm-crypt allocates the block with this size:
cc->dmreq_start + sizeof(struct dm_crypt_request) + cc->iv_size.

When accessing the initialization vector, dm-crypt uses the function
iv_of_dmreq, which performs this calculation: ALIGN((unsigned long)(dmreq
+ 1), crypto_ablkcipher_alignmask(any_tfm(cc)) + 1).

dm-crypt allocated "cc->iv_size" bytes beyond the end of dm_crypt_request
structure. However, when dm-crypt accesses the initialization vector, it
takes a pointer to the end of dm_crypt_request, aligns it, and then uses
it as the initialization vector. If the end of dm_crypt_request is not
aligned on a crypto_ablkcipher_alignmask(any_tfm(cc)) boundary the
alignment causes the initialization vector to point beyond the allocated

Fix this bug by calculating the variable iv_size_padding and adding it
to the allocated size.

Also correct the alignment of dm_crypt_request. struct dm_crypt_request
is specific to dm-crypt (it isn't used by the crypto subsystem at all),
so it is aligned on __alignof__(struct dm_crypt_request).

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
[wt: minor context adaptations, hopefully ok]
Signed-off-by: Willy Tarreau <w@xxxxxx>
drivers/md/dm-crypt.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 959d6d1..a44a908 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -998,6 +998,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
char *ivopts;
unsigned int key_size;
unsigned long long tmpll;
+ size_t iv_size_padding;

if (argc != 5) {
ti->error = "Not enough arguments";
@@ -1106,12 +1107,23 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)

cc->dmreq_start = sizeof(struct ablkcipher_request);
cc->dmreq_start += crypto_ablkcipher_reqsize(tfm);
- cc->dmreq_start = ALIGN(cc->dmreq_start, crypto_tfm_ctx_alignment());
- cc->dmreq_start += crypto_ablkcipher_alignmask(tfm) &
- ~(crypto_tfm_ctx_alignment() - 1);
+ cc->dmreq_start = ALIGN(cc->dmreq_start, __alignof__(struct dm_crypt_request));
+ if (crypto_ablkcipher_alignmask(tfm) < CRYPTO_MINALIGN) {
+ /* Allocate the padding exactly */
+ iv_size_padding = -(cc->dmreq_start + sizeof(struct dm_crypt_request))
+ & crypto_ablkcipher_alignmask(tfm);
+ } else {
+ /*
+ * If the cipher requires greater alignment than kmalloc
+ * alignment, we don't know the exact position of the
+ * initialization vector. We must assume worst case.
+ */
+ iv_size_padding = crypto_ablkcipher_alignmask(tfm);
+ }

cc->req_pool = mempool_create_kmalloc_pool(MIN_IOS, cc->dmreq_start +
- sizeof(struct dm_crypt_request) + cc->iv_size);
+ sizeof(struct dm_crypt_request) + iv_size_padding + cc->iv_size);
if (!cc->req_pool) {
ti->error = "Cannot allocate crypt request mempool";
goto bad_req_pool;

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