Re: [dm-devel] [PATCH 1/4] crypto: introduce CRYPTO_ALG_ALLOCATES_MEMORY

Mikulas Patocka
2020-06-17T15:08:54Z

I'm resending the patches with your comments resolved...

Mikulas

On Tue, 16 Jun 2020, Eric Biggers wrote:

> On Tue, Jun 16, 2020 at 11:01:31AM -0400, Mikulas Patocka wrote:
> > Introduce a new flag CRYPTO_ALG_ALLOCATES_MEMORY and modify dm-crypt, so
> > that it uses only drivers without this flag.
> >
> > If the flag is set, then the crypto driver allocates memory in its request
> > routine. Such drivers are not suitable for disk encryption because
> > GFP_ATOMIC allocation can fail anytime (causing random I/O errors) and
> > GFP_KERNEL allocation can recurse into the block layer, causing a
> > deadlock.
> >
> > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> >
> > Index: linux-2.6/include/linux/crypto.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/crypto.h
> > +++ linux-2.6/include/linux/crypto.h
> > @@ -97,9 +97,15 @@
> > #define CRYPTO_ALG_OPTIONAL_KEY 0x00004000
> >
> > /*
> > + * The driver is allocating emmory in its encrypt or decrypt callback,
> > + * so it should not be used to encrypt block devices.
> > + */
>
> "is allocating emmory" => "may allocate memory"
>
> "so it should not be used to encrypt block devices" =>
> "so it shouldn't be used in cases where memory allocation failures aren't
> acceptable, such as during block device encryption".
>
> Also, which types of algorithms does this flag apply to? E.g. if it applies to
> hash algorithms too, it's not sufficient to say "encrypt or decrypt callback".
>
> How about:
>
> /*
> * The driver may allocate memory during request processing, so it shouldn't be
> * used in cases where memory allocation failures aren't acceptable, such as
> * during block device encryption.
> */
>
> > +#define CRYPTO_ALG_ALLOCATES_MEMORY 0x00008000
> > +
> > +/*
> > * Don't trigger module loading
> > */
> > -#define CRYPTO_NOLOAD 0x00008000
> > +#define CRYPTO_NOLOAD 0x00010000
> >
> > /*
> > * Transform masks and values (for crt_flags).
> > Index: linux-2.6/drivers/md/dm-crypt.c
> > ===================================================================
>
> This would better belong as two separate patches: one to introduce
> CRYPTO_ALG_ALLOCATES_MEMORY, and one to make dm-crypt use it.
>
> > --- linux-2.6.orig/drivers/md/dm-crypt.c
> > +++ linux-2.6/drivers/md/dm-crypt.c
> > @@ -419,7 +419,7 @@ static int crypt_iv_lmk_ctr(struct crypt
> > return -EINVAL;
> > }
> >
> > - lmk->hash_tfm = crypto_alloc_shash("md5", 0, 0);
> > + lmk->hash_tfm = crypto_alloc_shash("md5", 0, CRYPTO_ALG_ALLOCATES_MEMORY);
> > if (IS_ERR(lmk->hash_tfm)) {
> > ti->error = "Error initializing LMK hash";
> > return PTR_ERR(lmk->hash_tfm);
> > @@ -581,7 +581,7 @@ static int crypt_iv_tcw_ctr(struct crypt
> > return -EINVAL;
> > }
> >
> > - tcw->crc32_tfm = crypto_alloc_shash("crc32", 0, 0);
> > + tcw->crc32_tfm = crypto_alloc_shash("crc32", 0, CRYPTO_ALG_ALLOCATES_MEMORY);
> > if (IS_ERR(tcw->crc32_tfm)) {
> > ti->error = "Error initializing CRC32 in TCW";
> > return PTR_ERR(tcw->crc32_tfm);
> > @@ -768,7 +768,7 @@ static int crypt_iv_elephant_ctr(struct
> > struct iv_elephant_private *elephant = &cc->iv_gen_private.elephant;
> > int r;
> >
> > - elephant->tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
> > + elephant->tfm = crypto_alloc_skcipher("ecb(aes)", 0, CRYPTO_ALG_ALLOCATES_MEMORY);
> > if (IS_ERR(elephant->tfm)) {
> > r = PTR_ERR(elephant->tfm);
> > elephant->tfm = NULL;
> > @@ -2088,7 +2088,7 @@ static int crypt_alloc_tfms_skcipher(str
> > return -ENOMEM;
> >
> > for (i = 0; i < cc->tfms_count; i++) {
> > - cc->cipher_tfm.tfms[i] = crypto_alloc_skcipher(ciphermode, 0, 0);
> > + cc->cipher_tfm.tfms[i] = crypto_alloc_skcipher(ciphermode, 0, CRYPTO_ALG_ALLOCATES_MEMORY);
>
> Despite the recent relaxation in rules, the preferred length of a line is still
> 80 columns.
>
> - Eric
>