[PATCH 3/9] fs/ext4: Disallow encryption if inode is DAX

ira.weiny
2020-05-13T05:43:38Z

From: Ira Weiny <ira.weiny@intel.com>

Encryption and DAX are incompatible. Changing the DAX mode due to a
change in Encryption mode is wrong without a corresponding
address_space_operations update.

Make the 2 options mutually exclusive by returning an error if DAX was
set first.

Furthermore, clarify the documentation of the exclusivity and how that
will work.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Changes:
remove WARN_ON_ONCE
Add documentation to the encrypt doc WRT DAX
---
Documentation/filesystems/fscrypt.rst | 4 +++-
fs/ext4/super.c | 10 +---------
2 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index aa072112cfff..1475b8d52fef 100644
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -1038,7 +1038,9 @@ astute users may notice some differences in behavior:
- The ext4 filesystem does not support data journaling with encrypted
regular files. It will fall back to ordered data mode instead.

-- DAX (Direct Access) is not supported on encrypted files.
+- DAX (Direct Access) is not supported on encrypted files. Attempts to enable
+ DAX on an encrypted file will fail. Mount options will _not_ enable DAX on
+ encrypted files.

- The st_size of an encrypted symlink will not necessarily give the
length of the symlink target as required by POSIX. It will actually
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index bf5fcb477f66..9873ab27e3fa 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1320,7 +1320,7 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
if (inode->i_ino == EXT4_ROOT_INO)
return -EPERM;

- if (WARN_ON_ONCE(IS_DAX(inode) && i_size_read(inode)))
+ if (IS_DAX(inode))
return -EINVAL;

res = ext4_convert_inline_data(inode);
@@ -1344,10 +1344,6 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
ext4_clear_inode_state(inode,
EXT4_STATE_MAY_INLINE_DATA);
- /*
- * Update inode->i_flags - S_ENCRYPTED will be enabled,
- * S_DAX may be disabled
- */
ext4_set_inode_flags(inode);
}
return res;
@@ -1371,10 +1367,6 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
ctx, len, 0);
if (!res) {
ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
- /*
- * Update inode->i_flags - S_ENCRYPTED will be enabled,
- * S_DAX may be disabled
- */
ext4_set_inode_flags(inode);
res = ext4_mark_inode_dirty(handle, inode);
if (res)
--
2.25.1