From: Eric Biggers Date: Sun, 19 Jul 2026 03:31:20 +0000 (-0700) Subject: fscrypt: Add missing superblock check in find_or_insert_direct_key() X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=b5fa40226e71c17847b9ff2816c6ca4133d0d994;p=thirdparty%2Fkernel%2Flinux.git fscrypt: Add missing superblock check in find_or_insert_direct_key() The legacy 'fscrypt_direct_keys' table caches master keys that are used by v1 encryption policies that have FSCRYPT_POLICY_FLAG_DIRECT_KEY. It's just a global table for all filesystems (since the keys can be provided by the legacy process-subscribed keyrings mechanism, which makes it difficult to reuse super_block::s_master_keys). The entries in it ('struct fscrypt_direct_key') do contain a super_block pointer, though, for passing to fscrypt_destroy_inline_crypt_key() when the last inode that references the key is evicted. However, when finding the fscrypt_direct_key for an inode, we weren't actually comparing the super_block pointer. As a result, inodes with different super_blocks could point to the same fscrypt_direct_key. That could extend the lifetime of a fscrypt_direct_key beyond the super_block it points to, causing a use-after-free later. Fix this by creating distinct fscrypt_direct_key structs for distinct super_block structs. Note that this problem doesn't exist in the v2 policy equivalent ("per-mode keys"), since the data structures there are per super_block. Fixes: 22e9947a4b2b ("fscrypt: stop holding extra request_queue references") Cc: stable@vger.kernel.org Reported-by: Sashiko Closes: https://sashiko.dev/#/patchset/20260717044303.425265-1-ebiggers%40kernel.org Reviewed-by: Christoph Hellwig Link: https://patch.msgid.link/20260719033120.122120-1-ebiggers@kernel.org Signed-off-by: Eric Biggers --- diff --git a/fs/crypto/keysetup_v1.c b/fs/crypto/keysetup_v1.c index e6e527c73f16..7e3a58dc4b56 100644 --- a/fs/crypto/keysetup_v1.c +++ b/fs/crypto/keysetup_v1.c @@ -147,13 +147,19 @@ find_or_insert_direct_key(struct fscrypt_direct_key *to_insert, if (memcmp(ci->ci_policy.v1.master_key_descriptor, dk->dk_descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0) continue; + /* The sb is used at eviction time, so it must be the same. */ + if (ci->ci_inode->i_sb != dk->dk_sb) + continue; if (ci->ci_mode != dk->dk_mode) continue; if (!fscrypt_is_key_prepared(&dk->dk_key, ci)) continue; if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize)) continue; - /* using existing tfm with same (descriptor, mode, raw_key) */ + /* + * Use an existing prepared key with the same (descriptor, sb, + * mode, inlinecrypt, raw_key) combination. + */ refcount_inc(&dk->dk_refcount); spin_unlock(&fscrypt_direct_keys_lock); free_direct_key(to_insert);