blk_crypto_fallback_start_using_mode() sets tfms_inited[] with smp_store_release(), but blk_crypto_fallback_bio_prep() reads it without smp_load_acquire() and without any lock protection. Most callers are covered by blk-crypto itself: a task whose key needs the fallback acquires the flag in the fast path of blk_crypto_fallback_start_using_mode(), and its slow path is serialized by tfms_init_lock. But the problem can still be actually triggered: a task can inherit a key without ever calling blk_crypto_start_using_key() itself, e.g. on the lockless per-mode key cache hit in setup_per_mode_enc_key(). And bios reach the dm target via srcu_dereference()/rcu_dereference(), neither of which provides an acquire for tfms_inited[]. As a result, on a weakly ordered machine, the flag can be seen as false and fail I/O, or as true while the tfms[] and fallback profile initialization ordered before it is still invisible, and the reads that follow can crash in the fallback I/O path. Fix this by pairing the read with the release in blk_crypto_fallback_start_using_mode() using smp_load_acquire(), and hoist bc->bc_key->crypto_cfg into a local variable. The plain read dates back to commit 488f6682c832 ("block: blk-crypto-fallback for Inline Encryption") in v5.8, but was masked by the smp_load_acquire() in fscrypt_is_key_prepared(); commit dd015b566d50 ("fscrypt: Fix key setup in edge case with multiple data unit sizes") in v7.2 replaced that with RCU publish/subscribe. Fixes: 488f6682c832 ("block: blk-crypto-fallback for Inline Encryption") Cc: stable@vger.kernel.org Signed-off-by: Baokun Li --- block/blk-crypto-fallback.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/block/blk-crypto-fallback.c b/block/blk-crypto-fallback.c index b5dbb092caea..31f76d117593 100644 --- a/block/blk-crypto-fallback.c +++ b/block/blk-crypto-fallback.c @@ -488,15 +488,17 @@ static void blk_crypto_fallback_decrypt_endio(struct bio *bio) bool blk_crypto_fallback_bio_prep(struct bio *bio) { struct bio_crypt_ctx *bc = bio->bi_crypt_context; + const struct blk_crypto_config *cfg = &bc->bc_key->crypto_cfg; struct bio_fallback_crypt_ctx *f_ctx; - if (WARN_ON_ONCE(!tfms_inited[bc->bc_key->crypto_cfg.crypto_mode])) { + /* Pairs with the release in blk_crypto_fallback_start_using_mode(). */ + if (WARN_ON_ONCE(!smp_load_acquire(&tfms_inited[cfg->crypto_mode]))) { /* User didn't call blk_crypto_start_using_key() first */ bio_io_error(bio); return false; } - if (bc->bc_key->crypto_cfg.key_type != BLK_CRYPTO_KEY_TYPE_RAW) { + if (cfg->key_type != BLK_CRYPTO_KEY_TYPE_RAW) { bio_endio_status(bio, BLK_STS_NOTSUPP); return false; } -- 2.43.7