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 returning early from blk_crypto_fallback_evict_key() when tfms_inited[] is not set for the key's mode. tfms_inited[] is only set after blk_crypto_fallback_init() has successfully initialized the profile, so the crash above is no longer reachable. 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 Closes: https://patch.msgid.link/sashiko-outbox-167341@kernel.org Suggested-by: Eric Biggers Link: https://patch.msgid.link/20261014155131.GB322435@quark Signed-off-by: Baokun Li --- Changes since v2: * Skip fallback eviction if tfms_inited[] is unset (Suggested by Eric Biggers). * Drop v2 2/2; fix the weak ordering in fscrypt instead (Suggested by Eric Biggers). Changes since v1: * Publish the profile only after successful init to avoid concurrent UAF (Reported by Sashiko). v2: https://patch.msgid.link/20261014071846.3666398-1-libaokun@linux.alibaba.com v1: https://patch.msgid.link/20261013095106.881914-1-libaokun@linux.alibaba.com block/blk-crypto-fallback.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/block/blk-crypto-fallback.c b/block/blk-crypto-fallback.c index 2a8f40a65158..12e0b487e23a 100644 --- a/block/blk-crypto-fallback.c +++ b/block/blk-crypto-fallback.c @@ -524,6 +524,12 @@ bool blk_crypto_fallback_bio_prep(struct bio *bio) int blk_crypto_fallback_evict_key(const struct blk_crypto_key *key) { + /* + * 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; return __blk_crypto_evict_key(blk_crypto_fallback_profile, key); } base-commit: 734bef548a96e8774d6eef5dfa2026c6edc4e80b -- 2.43.7