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Fix locking and a double free in fsops rename and unlink #615

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Fix locking and a double free in fsops rename and unlink #615

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253612d
fix: releases of unheld meta_lock in rename and unlink error paths
matejk Aug 17, 2026
3800dcb
fix: double free of the new name on a late rename failure
matejk Aug 17, 2026
f9aa71c
fix: check for a non-empty directory before taking parent->meta_lock …
matejk Aug 19, 2026
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58 changes: 33 additions & 25 deletions src/libltfs/ltfs_fsops.c
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Original file line number Diff line number Diff line change
Expand Up @@ -460,6 +460,26 @@ int ltfs_fsops_unlink(const char *path, ltfs_file_id *id, struct ltfs_volume *vo
}
parent = d->parent;

/* Can't remove non-empty directories */
if (d->isdir) {
ret = 0;
acquireread_mrsw(&d->contents_lock);
if (HASH_COUNT(d->child_list) != 0)
ret = -LTFS_DIRNOTEMPTY;
releaseread_mrsw(&d->contents_lock);
if (ret < 0) {
releasewrite_mrsw(&parent->contents_lock);
fs_release_dentry(parent);
releaseread_mrsw(&vol->lock);
free(path_norm);
fs_release_dentry(d);
return ret;
}
}

/* Lock order: parent contents_lock, parent meta_lock, then child meta_lock */
acquirewrite_mrsw(&parent->meta_lock);

Comment on lines +480 to +482

@XV02 XV02 Aug 18, 2026

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Moving acquirewrite_mrsw(&parent->meta_lock) above the WORM and non-empty-dir checks fixes the original "release of unheld lock" bug, but creates a lock-order inversion with the non-empty-dir check. Every other site in this file (and the rest of the codebase) acquires contents_lock before meta_lock on the same node, and parent locks before child locks. Here the order is reversed: parent meta_lock is held when a child's contents_lock is taken. Any concurrent thread that holds d->contents_lock (e.g. a readdir) and then tries to acquire parent->meta_lock will deadlock with this path.

@matejk matejk Aug 19, 2026 •
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I don't think this is an inversion, but I have reordered the code so the pairing no longer occurs.

The documented order (struct dentry, ltfs.h:279) is: "contents_lock, meta_lock ... take all parent locks before any dentry locks." Parent contents -> parent meta -> child contents -> child meta is that rule, and it is the order fs_path_lookup itself uses (fs.c:627-640). A deadlock would need the inverse pair - a child contents_lock held while taking the parent's meta_lock - and no site in the tree does that; readdir takes d->contents_lock, releases it, then d->meta_lock, and never touches the parent's meta_lock.

Still, the non-empty check only needs the child's contents_lock, so it now runs before parent->meta_lock is taken (new commit). parent->meta_lock is held only for the WORM checks and the unlink, never while d->contents_lock is acquired.

The original defect: the WORM and non-empty error paths went to out -> fs_release_dentry_unlocked(parent) -> releasewrite_mrsw(&parent->meta_lock), but the lock was only acquired later (old line 485), so they released a lock never held. The WORM flags are also meta_lock-protected (ltfs.h; written under d->meta_lock in xattr.c), so reading them without it was a second defect.

if (parent->is_immutable || parent->is_appendonly) {
ltfsmsg(LTFS_ERR, 17237E, "unlink: parent is WORM");
ret = -LTFS_WORM_ENABLED;
Expand All @@ -471,18 +491,6 @@ int ltfs_fsops_unlink(const char *path, ltfs_file_id *id, struct ltfs_volume *vo
goto out;
}

/* Can't remove non-empty directories */
if (d->isdir) {
ret = 0;
acquireread_mrsw(&d->contents_lock);
if (HASH_COUNT(d->child_list) != 0)
ret = -LTFS_DIRNOTEMPTY;
releaseread_mrsw(&d->contents_lock);
if (ret < 0)
goto out;
}

acquirewrite_mrsw(&parent->meta_lock);
acquirewrite_mrsw(&d->meta_lock);

if (dcache_initialized(vol)) {
Expand Down Expand Up @@ -640,19 +648,6 @@ int ltfs_fsops_rename(const char *from, const char *to, ltfs_file_id *id, struct
goto out_release;
}

if (fromdir->is_appendonly || fromdir->is_immutable ) {
ltfsmsg(LTFS_ERR, 17237E, "rename: parent is WORM");
ret = -LTFS_WORM_ENABLED;
acquirewrite_mrsw(&fromdir->meta_lock);
goto out_release;
}
if (todir->is_immutable || todir->is_appendonly) {
ltfsmsg(LTFS_ERR, 17237E, "rename: target dir is WORM");
ret = -LTFS_WORM_ENABLED;
acquirewrite_mrsw(&fromdir->meta_lock);
goto out_release;
}

/* Take locks in the appropriate order and look up the source and destination dentries */
if (todir == fromdir || fs_is_predecessor(todir, fromdir)) {
acquirewrite_mrsw(&todir->contents_lock);
Expand Down Expand Up @@ -760,6 +755,16 @@ int ltfs_fsops_rename(const char *from, const char *to, ltfs_file_id *id, struct
}
#endif

if (fromdir->is_immutable || fromdir->is_appendonly ||
todir->is_immutable || todir->is_appendonly) {
ltfsmsg(LTFS_ERR, 17237E, "rename: source or target dir is WORM");
ret = -LTFS_WORM_ENABLED;
fs_release_dentry(fromdentry);
if (todentry && todentry != fromdentry)
fs_release_dentry(todentry);
goto out_unlock;
}

if (fromdentry->is_immutable || fromdentry->is_appendonly) {
ltfsmsg(LTFS_ERR, 17237E, "rename: src entry is WORM");
ret = -LTFS_WORM_ENABLED;
Expand Down Expand Up @@ -857,6 +862,9 @@ int ltfs_fsops_rename(const char *from, const char *to, ltfs_file_id *id, struct
fromdentry->name.percent_encode = fs_is_percent_encode_required(fromdentry->name.name);
fromdentry->platform_safe_name = to_filename_copy2;
fromdentry->matches_name_criteria = index_criteria_match(fromdentry, vol);
/* fromdentry owns the buffers now; keep out_free from freeing them again */
to_filename_copy = NULL;
to_filename_copy2 = NULL;

/* Add fromdentry to new directory */
todir->child_list = fs_add_key_to_hash_table(todir->child_list, fromdentry, &ret);
Expand Down
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