[RFC,11/13] fscrypt: cache list of inlinecrypt devices

Commit Message

Sweet Tea Dorminy Sept. 2, 2023, 5:54 a.m. UTC

btrfs sometimes frees extents while holding a mutex, which makes it
impossible to free an inlinecrypt prepared key since that requires
taking a semaphore. Therefore, we will need to offload prepared key
freeing into an asynchronous process (rcu is insufficient since that can
run in softirq context which is also incompatible with taking a
semaphore). In order to avoid use-after-free on the filesystem
superblock for keys being freed during shutdown, we need to cache the
list of devices that the key has been loaded into, so that we can later
remove it without reference to the superblock.

Signed-off-by: Sweet Tea Dorminy <[e-mail]>
---
 fs/crypto/fscrypt_private.h | 13 +++++++++++--
 fs/crypto/inline_crypt.c    | 20 +++++++++-----------
 fs/crypto/keysetup.c        |  2 +-
 3 files changed, 21 insertions(+), 14 deletions(-)

Patch

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index cf1eb7fe546f..30459e219fc3 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -206,6 +206,16 @@  struct fscrypt_prepared_key {
 	struct crypto_skcipher *tfm;
 #ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
 	struct blk_crypto_key *blk_key;
+
+	/*
+	 * The list of devices that have this block key.
+	 */
+	struct block_device **devices;
+
+	/*
+	 * The number of devices in @ci_devices.
+	 */
+	size_t device_count;
 #endif
 	enum fscrypt_prepared_key_type type;
 };
@@ -472,8 +482,7 @@  int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
 				     const u8 *raw_key,
 				     const struct fscrypt_common_info *ci);
 
-void fscrypt_destroy_inline_crypt_key(struct super_block *sb,
-				      struct fscrypt_prepared_key *prep_key);
+void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key);
 
 /*
  * Check whether the crypto transform or blk-crypto key has been allocated in
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index f0229234249c..19ebdef8508b 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -185,12 +185,15 @@  int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
 		if (err)
 			break;
 	}
-	kfree(devs);
+
 	if (err) {
 		fscrypt_err(inode, "error %d starting to use blk-crypto", err);
 		goto fail;
 	}
 
+	prep_key->devices = devs;
+	prep_key->device_count = num_devs;
+
 	/*
 	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
 	 * I.e., here we publish ->blk_key with a RELEASE barrier so that
@@ -205,24 +208,19 @@  int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
 	return err;
 }
 
-void fscrypt_destroy_inline_crypt_key(struct super_block *sb,
-				      struct fscrypt_prepared_key *prep_key)
+void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key)
 {
 	struct blk_crypto_key *blk_key = prep_key->blk_key;
-	struct block_device **devs;
-	unsigned int num_devs;
 	unsigned int i;
 
 	if (!blk_key)
 		return;
 
 	/* Evict the key from all the filesystem's block devices. */
-	devs = fscrypt_get_devices(sb, &num_devs);
-	if (!IS_ERR(devs)) {
-		for (i = 0; i < num_devs; i++)
-			blk_crypto_evict_key(devs[i], blk_key);
-		kfree(devs);
-	}
+	for (i = 0; i < prep_key->device_count; i++)
+		blk_crypto_evict_key(prep_key->devices[i], blk_key);
+
+	kfree(prep_key->devices);
 	kfree_sensitive(blk_key);
 }
 
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index f0f70b888bd8..4ea9b68363d5 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -184,7 +184,7 @@  void fscrypt_destroy_prepared_key(struct super_block *sb,
 				  struct fscrypt_prepared_key *prep_key)
 {
 	crypto_free_skcipher(prep_key->tfm);
-	fscrypt_destroy_inline_crypt_key(sb, prep_key);
+	fscrypt_destroy_inline_crypt_key(prep_key);
 	memzero_explicit(prep_key, sizeof(*prep_key));
 }