linux-kernel - [PATCH] ext4: Fix no-key deletion for encrypt+casefold

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Date:   Sat, 22 May 2021 00:41:32 +0000
From:   Daniel Rosenberg <drosen@...gle.com>
To:     "Theodore Y . Ts'o" <tytso@....edu>,
        Eric Biggers <ebiggers@...nel.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel-team@...roid.com, Daniel Rosenberg <drosen@...gle.com>
Subject: [PATCH] ext4: Fix no-key deletion for encrypt+casefold

commit 471fbbea7ff7 ("ext4: handle casefolding with encryption") is
missing a few checks for the encryption key which are needed to
support deleting enrypted casefolded files when the key is not
present.

Note from ebiggers:
(These checks for the encryption key are still racy since they happen
too late, but apparently they worked well enough...)

This bug made it impossible to delete encrypted+casefolded directories
without the encryption key, due to errors like:

    W         : EXT4-fs warning (device vdc): __ext4fs_dirhash:270: inode #49202: comm Binder:378_4: Siphash requires key

Repro steps in kvm-xfstests test appliance:
      mkfs.ext4 -F -E encoding=utf8 -O encrypt /dev/vdc
      mount /vdc
      mkdir /vdc/dir
      chattr +F /vdc/dir
      keyid=$(head -c 64 /dev/zero | xfs_io -c add_enckey /vdc | awk '{print $NF}')
      xfs_io -c "set_encpolicy $keyid" /vdc/dir
      for i in `seq 1 100`; do
          mkdir /vdc/dir/$i
      done
      xfs_io -c "rm_enckey $keyid" /vdc
      rm -rf /vdc/dir # fails with the bug

Fixes: 471fbbea7ff7 ("ext4: handle casefolding with encryption")
Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
---
 fs/ext4/namei.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index afb9d05a99ba..a4af26d4459a 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1376,7 +1376,8 @@ int ext4_fname_setup_ci_filename(struct inode *dir, const struct qstr *iname,
 	struct dx_hash_info *hinfo = &name->hinfo;
 	int len;
 
-	if (!IS_CASEFOLDED(dir) || !dir->i_sb->s_encoding) {
+	if (!IS_CASEFOLDED(dir) || !dir->i_sb->s_encoding ||
+	    (IS_ENCRYPTED(dir) && !fscrypt_has_encryption_key(dir))) {
 		cf_name->name = NULL;
 		return 0;
 	}
@@ -1427,7 +1428,8 @@ static bool ext4_match(struct inode *parent,
 #endif
 
 #ifdef CONFIG_UNICODE
-	if (parent->i_sb->s_encoding && IS_CASEFOLDED(parent)) {
+	if (parent->i_sb->s_encoding && IS_CASEFOLDED(parent) &&
+	    (!IS_ENCRYPTED(parent) || fscrypt_has_encryption_key(parent))) {
 		if (fname->cf_name.name) {
 			struct qstr cf = {.name = fname->cf_name.name,
 					  .len = fname->cf_name.len};
-- 
2.31.1.818.g46aad6cb9e-goog