When a blk_crypto_key starts being used or is evicted, fs/crypto/ calls
fscrypt_get_devices() to get the filesystem's list of block devices,
then iterates over them and calls blk_crypto_config_supported(),
blk_crypto_start_using_key(), or blk_crypto_evict_key() on each one.
Currently, the block device pointers are placed in a dynamically
allocated array. This dynamic allocation is problematic because:
- It can fail, especially at the fscrypt_destroy_inline_crypt_key() call
site when it's invoked for inode eviction under direct reclaim.
- fscrypt_destroy_inline_crypt_key() doesn't handle the failure. It
just zeroizes and frees the blk_crypto_key without calling
blk_crypto_evict_key(). That causes a use-after-free.
For now, let's fix this in the straightforward and easily-backportable
way by switching to an on-stack array. Currently the fscrypt
multi-device functionality is used only by f2fs, which has a hardcoded
limit of 8 block devices. An on-stack array works fine for that.
(Of course, this solution won't scale up to large number of block
devices. For that we'd need a different solution, like moving the block
device iteration into the filesystem. Or in the case of btrfs, which
will only support blk-crypto-fallback, we should make it just call
blk-crypto-fallback directly, so the block devices won't be needed.)
Fixes: 22e9947a4b2b ("fscrypt: stop holding extra request_queue references")
Cc: [email protected]
Signed-off-by: Eric Biggers <[email protected]>
---
fs/crypto/inline_crypt.c | 57 ++++++++++++++--------------------------
fs/f2fs/super.c | 25 ++++++++++--------
include/linux/fscrypt.h | 18 +++++++------
3 files changed, 44 insertions(+), 56 deletions(-)
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index 47324062fee51..66b9c9150fed6 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -22,22 +22,14 @@
#include "fscrypt_private.h"
-static struct block_device **fscrypt_get_devices(struct super_block *sb,
- unsigned int *num_devs)
+static unsigned int
+fscrypt_get_devices(struct super_block *sb,
+ struct block_device *devs[FSCRYPT_MAX_DEVICES])
{
- struct block_device **devs;
-
- if (sb->s_cop->get_devices) {
- devs = sb->s_cop->get_devices(sb, num_devs);
- if (devs)
- return devs;
- }
- devs = kmalloc_obj(*devs);
- if (!devs)
- return ERR_PTR(-ENOMEM);
+ if (sb->s_cop->get_devices)
+ return sb->s_cop->get_devices(sb, devs);
devs[0] = sb->s_bdev;
- *num_devs = 1;
- return devs;
+ return 1;
}
static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_inode_info *ci)
@@ -96,7 +88,7 @@ int fscrypt_select_encryption_impl(struct fscrypt_inode_info
*ci,
const struct inode *inode = ci->ci_inode;
struct super_block *sb = inode->i_sb;
struct blk_crypto_config crypto_cfg;
- struct block_device **devs;
+ struct block_device *devs[FSCRYPT_MAX_DEVICES];
unsigned int num_devs;
unsigned int i;
@@ -135,20 +127,15 @@ int fscrypt_select_encryption_impl(struct
fscrypt_inode_info *ci,
crypto_cfg.key_type = is_hw_wrapped_key ?
BLK_CRYPTO_KEY_TYPE_HW_WRAPPED : BLK_CRYPTO_KEY_TYPE_RAW;
- devs = fscrypt_get_devices(sb, &num_devs);
- if (IS_ERR(devs))
- return PTR_ERR(devs);
-
+ num_devs = fscrypt_get_devices(sb, devs);
for (i = 0; i < num_devs; i++) {
if (!blk_crypto_config_supported(devs[i], &crypto_cfg))
- goto out_free_devs;
+ return 0;
}
fscrypt_log_blk_crypto_impl(ci->ci_mode, devs, num_devs, &crypto_cfg);
ci->ci_inlinecrypt = true;
-out_free_devs:
- kfree(devs);
return 0;
}
@@ -164,7 +151,7 @@ int fscrypt_prepare_inline_crypt_key(struct
fscrypt_prepared_key *prep_key,
enum blk_crypto_key_type key_type = is_hw_wrapped ?
BLK_CRYPTO_KEY_TYPE_HW_WRAPPED : BLK_CRYPTO_KEY_TYPE_RAW;
struct blk_crypto_key *blk_key;
- struct block_device **devs;
+ struct block_device *devs[FSCRYPT_MAX_DEVICES];
unsigned int num_devs;
unsigned int i;
int err;
@@ -182,17 +169,12 @@ int fscrypt_prepare_inline_crypt_key(struct
fscrypt_prepared_key *prep_key,
}
/* Start using blk-crypto on all the filesystem's block devices. */
- devs = fscrypt_get_devices(sb, &num_devs);
- if (IS_ERR(devs)) {
- err = PTR_ERR(devs);
- goto fail;
- }
+ num_devs = fscrypt_get_devices(sb, devs);
for (i = 0; i < num_devs; i++) {
err = blk_crypto_start_using_key(devs[i], blk_key);
if (err)
break;
}
- kfree(devs);
if (err) {
fscrypt_err(inode, "error %d starting to use blk-crypto", err);
goto fail;
@@ -210,20 +192,21 @@ void fscrypt_destroy_inline_crypt_key(struct super_block
*sb,
struct fscrypt_prepared_key *prep_key)
{
struct blk_crypto_key *blk_key = prep_key->blk_key;
- struct block_device **devs;
+ struct block_device *devs[FSCRYPT_MAX_DEVICES];
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);
- }
+ /*
+ * Evict the key from all the filesystem's block devices.
+ * This *must* be done before the key is freed.
+ */
+ num_devs = fscrypt_get_devices(sb, devs);
+ for (i = 0; i < num_devs; i++)
+ blk_crypto_evict_key(devs[i], blk_key);
+
kfree_sensitive(blk_key);
}
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 2b8d964111562..9760e4efeffec 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -3749,24 +3749,27 @@ static bool f2fs_has_stable_inodes(struct super_block
*sb)
return true;
}
-static struct block_device **f2fs_get_devices(struct super_block *sb,
- unsigned int *num_devs)
+static unsigned int
+f2fs_get_devices(struct super_block *sb,
+ struct block_device *devs[FSCRYPT_MAX_DEVICES])
{
struct f2fs_sb_info *sbi = F2FS_SB(sb);
- struct block_device **devs;
+ int ndevs;
int i;
- if (!f2fs_is_multi_device(sbi))
- return NULL;
+ static_assert(MAX_DEVICES <= FSCRYPT_MAX_DEVICES);
- devs = kmalloc_objs(*devs, sbi->s_ndevs);
- if (!devs)
- return ERR_PTR(-ENOMEM);
+ if (!f2fs_is_multi_device(sbi)) {
+ devs[0] = sb->s_bdev;
+ return 1;
+ }
+ ndevs = sbi->s_ndevs;
+ if (WARN_ON_ONCE(ndevs > FSCRYPT_MAX_DEVICES))
+ ndevs = FSCRYPT_MAX_DEVICES;
- for (i = 0; i < sbi->s_ndevs; i++)
+ for (i = 0; i < ndevs; i++)
devs[i] = FDEV(i).bdev;
- *num_devs = sbi->s_ndevs;
- return devs;
+ return ndevs;
}
static const struct fscrypt_operations f2fs_cryptops = {
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 54712ec61ffb7..f6b235cd72b45 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -57,6 +57,9 @@ struct fscrypt_name {
/* Maximum value for the third parameter of fscrypt_operations.set_context().
*/
#define FSCRYPT_SET_CONTEXT_MAX_SIZE 40
+/* Maximum supported number of block devices per filesystem */
+#define FSCRYPT_MAX_DEVICES 8
+
#ifdef CONFIG_FS_ENCRYPTION
/* Crypto operations for filesystems */
@@ -181,21 +184,20 @@ struct fscrypt_operations {
bool (*has_stable_inodes)(struct super_block *sb);
/*
- * Return an array of pointers to the block devices to which the
- * filesystem may write encrypted file contents, NULL if the filesystem
- * only has a single such block device, or an ERR_PTR() on error.
+ * Retrieve the list of block devices to which the filesystem may write
+ * encrypted file contents.
*
- * On successful non-NULL return, *num_devs is set to the number of
- * devices in the returned array. The caller must free the returned
- * array using kfree().
+ * This writes the block_device pointers to @devs and returns the count
+ * (between 1 and FSCRYPT_MAX_DEVICES inclusively).
*
* If the filesystem can use multiple block devices (other than block
* devices that aren't used for encrypted file contents, such as
* external journal devices), and wants to support inline encryption,
* then it must implement this function. Otherwise it's not needed.
*/
- struct block_device **(*get_devices)(struct super_block *sb,
- unsigned int *num_devs);
+ unsigned int (*get_devices)(
+ struct super_block *sb,
+ struct block_device *devs[FSCRYPT_MAX_DEVICES]);
};
int fscrypt_d_revalidate(struct inode *dir, const struct qstr *name,
base-commit: f2ec6312bf711369561bdcb22f8a63c0b118c479
--
2.55.0
