[PATCH 4/5] xfs: allow unlinked symlinks and dirs with zero size

Darrick J. Wong
2024-06-12T17:47:35Z

From: Darrick J. Wong <djwong@kernel.org>

For a very very long time, inode inactivation has set the inode size to
zero before unmapping the extents associated with the data fork.
Unfortunately, commit 3c6f46eacd876 changed the inode verifier to
prohibit zero-length symlinks and directories. If an inode happens to
get logged in this state and the system crashes before freeing the
inode, log recovery will also fail on the broken inode.

Therefore, allow zero-size symlinks and directories as long as the link
count is zero; nobody will be able to open these files by handle so
there isn't any risk of data exposure.

Fixes: 3c6f46eacd876 ("xfs: sanity check directory inode di_size")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/libxfs/xfs_inode_buf.c | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
index e7a7bfbe75b4..513b50da6215 100644
--- a/fs/xfs/libxfs/xfs_inode_buf.c
+++ b/fs/xfs/libxfs/xfs_inode_buf.c
@@ -379,10 +379,13 @@ xfs_dinode_verify_fork(
/*
* A directory small enough to fit in the inode must be stored
* in local format. The directory sf <-> extents conversion
- * code updates the directory size accordingly.
+ * code updates the directory size accordingly. Directories
+ * being truncated have zero size and are not subject to this
+ * check.
*/
if (S_ISDIR(mode)) {
- if (be64_to_cpu(dip->di_size) <= fork_size &&
+ if (dip->di_size &&
+ be64_to_cpu(dip->di_size) <= fork_size &&
fork_format != XFS_DINODE_FMT_LOCAL)
return __this_address;
}
@@ -528,9 +531,19 @@ xfs_dinode_verify(
if (mode && xfs_mode_to_ftype(mode) == XFS_DIR3_FT_UNKNOWN)
return __this_address;

- /* No zero-length symlinks/dirs. */
- if ((S_ISLNK(mode) || S_ISDIR(mode)) && di_size == 0)
- return __this_address;
+ /*
+ * No zero-length symlinks/dirs unless they're unlinked and hence being
+ * inactivated.
+ */
+ if ((S_ISLNK(mode) || S_ISDIR(mode)) && di_size == 0) {
+ if (dip->di_version > 1) {
+ if (dip->di_nlink)
+ return __this_address;
+ } else {
+ if (dip->di_onlink)
+ return __this_address;
+ }
+ }

fa = xfs_dinode_verify_nrext64(mp, dip);
if (fa)