Re: [PATCH v2 1/2] blk-crypto: fix NULL deref and UAF in __blk_crypto_evict_key()

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Oct 14, 2026 at 03:18:45PM +0800, Baokun Li wrote:
> Sashiko reported a possible NULL pointer dereference, triggered by the
> following flow:
> 
>   dm-inlinecrypt ctor            # first use of the fallback
>    ├─ blk_crypto_init_key()      # succeeds, ctx->key.size != 0
>    ├─ blk_crypto_start_using_key()
>    │   ├─ hw-wrapped key: -EOPNOTSUPP
>    │   │    # profile never allocated (NULL)
>    │   └─ raw key: fallback_start_using_mode()
>    │      └─ blk_crypto_fallback_init() fails
>    │         └─ kfree(profile)   # not NULLed
>    ├─ goto bad
>    └─ inlinecrypt_dtr()          # evicts whenever key.size is set
>       └─ blk_crypto_evict_key()
>          └─ blk_crypto_config_supported_natively() = false
>             └─ blk_crypto_fallback_evict_key()
>                └─ __blk_crypto_evict_key(blk_crypto_fallback_profile)
>                   └─ profile->num_slots # BOOM!!!
> 
> This issue can be reproduced using the following commands:
> 
>   dd if=/dev/zero of=/tmp/backing bs=1M count=64
>   LOOP=$(losetup -f --show /tmp/backing)
>   SZ=$(blockdev --getsz $LOOP)
>   KEY=$(head -c 64 /dev/urandom | od -An -tx1 | tr -d ' \n')
>   dmsetup create ic --table "0 $SZ inlinecrypt aes-xts-plain64 \
>     $KEY 0 $LOOP 0 1 keytype:hw-wrapped"
> 
> And the following oops is triggered:
> 
>   ==================================================================
>   blk-crypto: loop0: no support for wrapped keys
>   Oops: general protection fault, probably for non-canonical address
>         0xdffffc000000000b: 0000 [#1] SMP KASAN PTI
>   KASAN: null-ptr-deref in range [0x0000000000000058-0x000000000000005f]
>   CPU: 5 UID: 0 PID: 901 Comm: dmsetup 7.3.0-rc3 #1 PREEMPT(lazy)
>   RIP: 0010:__blk_crypto_evict_key+0x2e/0x3b0
>   Call Trace:
>    blk_crypto_evict_key+0x24c/0x320
>    inlinecrypt_dtr+0xf6/0x160
>    inlinecrypt_ctr+0x2d3/0xbd0
>    dm_table_add_target+0x661/0xf40
>    table_load+0x1c4/0x490
>    ctl_ioctl+0x32f/0x5f0
>    dm_ctl_ioctl+0xe/0x20
>   ==================================================================
> 
> dm-inlinecrypt is the only caller that can evict a key that was never
> started, as fscrypt frees such a key without evicting it.
> 
> Fix this by publishing blk_crypto_fallback_profile only after
> blk_crypto_fallback_init() succeeds, and by returning early from
> __blk_crypto_evict_key() when the profile is NULL.  The eviction path
> can then only observe either a NULL profile or a fully initialized
> profile that is never freed.  A key whose start failed cannot be in a
> keyslot, so there is nothing to evict.
> 
> The profile pointer is published and read locklessly, so use
> smp_store_release()/smp_load_acquire() to guarantee that a reader in
> the eviction path that observes the pointer also observes the
> initialized profile.
> 
> The bug has been latent since commit c984ff1423ae ("blk-crypto:
> dynamically allocate fallback profile") was merged in v6.5, and only
> became actually triggerable when commit e7f57d2c47e2 ("dm-inlinecrypt:
> add target for inline block device encryption") was merged in v7.2.
> 
> Fixes: c984ff1423ae ("blk-crypto: dynamically allocate fallback profile")
> Cc: stable@vger.kernel.org
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://patch.msgid.link/sashiko-outbox-167341@kernel.org
> Signed-off-by: Baokun Li <libaokun@linux.alibaba.com>
> ---
>  block/blk-crypto-fallback.c | 31 +++++++++++++++++++------------
>  block/blk-crypto-profile.c  |  3 +++
>  2 files changed, 22 insertions(+), 12 deletions(-)

Wouldn't it be a lot simpler to just make
blk_crypto_fallback_evict_key() check the existing tfms_inited flag?

	/*
	 * Pairs with smp_store_release() in
	 * blk_crypto_fallback_start_using_mode()
	 */
	if (!smp_load_acquire(&tfms_inited[key->crypto_cfg.crypto_mode]))
		return 0;