On 2026/10/14 23:51, Eric Biggers wrote:
> 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: [email protected]
>> Reported-by: Sashiko <[email protected]>
>> Closes: https://patch.msgid.link/[email protected]
>> Signed-off-by: Baokun Li <[email protected]>
>> ---
>> 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;
Indeed, this is a simpler and more straightforward approach.
I will use it in the next iteration.
Thank you for your suggestion!
Regards,
Baokun
