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Eric Biggers
6fe4e4b825
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: 22e9947a4b ("fscrypt: stop holding extra request_queue references")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260713023708.9245-1-ebiggers%40kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260719055602.78828-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>