5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Michael Bommarito <redacted>
commit 526c49cff3f72c3ec74752016380c7567040581b upstream.
nlm_traverse_files() pins the current file with f_count++ across
a mutex_unlock for nlm_inspect_file(), but nothing pins the saved
next pointer. A concurrent nlm_release_file() can kfree the next
file during the unlock window, and the iterator dereferences freed
memory on the next loop step.
Pin both current and next before the lock-drop. Advance by
swapping the pinned cursors at the end of each iteration so next
is always held alive across the unlock.
Always call nlm_file_release() after dropping the iteration pin,
regardless of whether the file matched the predicate. Use
nlm_file_inuse(), which does a live walk of the inode lock list,
rather than the cached f_locks field, so skipped files that never
ran nlm_inspect_file() are evaluated correctly.
Because every file in a hash bucket is now pinned and released,
files skipped by the is_failover_file predicate that have no
locks, blocks, shares, or external references are deleted during
traversal. The old code never evaluated skipped files for
cleanup. The new behavior is intentional: such files are stale
and should not persist in the table.
Fixes: 01df9c5e918a ("LOCKD: Fix a deadlock in nlm_traverse_files()")
Cc: <redacted>
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <redacted>
Link: https://patch.msgid.link/20260524115527.1734251-1-michael.bommarito@gmail.com (local)
Signed-off-by: Chuck Lever <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/lockd/svcsubs.c | 53 ++++++++++++++++++++++++++++++-----------------------
1 file changed, 30 insertions(+), 23 deletions(-)
--- a/fs/lockd/svcsubs.c
+++ b/fs/lockd/svcsubs.c
@@ -286,12 +286,10 @@ nlm_file_inuse(struct nlm_file *file)
return 0;
}
-static void nlm_close_files(struct nlm_file *file)
+static void nlm_file_release(struct nlm_file *file)
{
- if (file->f_file[O_RDONLY])
- nlmsvc_ops->fclose(file->f_file[O_RDONLY]);
- if (file->f_file[O_WRONLY])
- nlmsvc_ops->fclose(file->f_file[O_WRONLY]);
+ if (!nlm_file_inuse(file))
+ nlm_delete_file(file);
}
/*@@ -301,32 +299,41 @@ static int
nlm_traverse_files(void *data, nlm_host_match_fn_t match,
int (*is_failover_file)(void *data, struct nlm_file *file))
{
- struct hlist_node *next;
- struct nlm_file *file;
+ struct nlm_file *file, *next;
int i, ret = 0;
mutex_lock(&nlm_file_mutex);
for (i = 0; i < FILE_NRHASH; i++) {
- hlist_for_each_entry_safe(file, next, &nlm_files[i], f_list) {
- if (is_failover_file && !is_failover_file(data, file))
- continue;
+ file = hlist_entry_safe(nlm_files[i].first,
+ struct nlm_file, f_list);
+ if (file)
file->f_count++;
- mutex_unlock(&nlm_file_mutex);
+ while (file) {
+ /*
+ * Pin the next neighbour before we drop the mutex
+ * for nlm_inspect_file(); a concurrent
+ * nlm_release_file() under the same mutex would
+ * otherwise be free to unlink and kfree it during
+ * the unlock window, leaving us to dereference a
+ * freed slab when we walked to next afterwards.
+ */
+ next = hlist_entry_safe(file->f_list.next,
+ struct nlm_file, f_list);
+ if (next)
+ next->f_count++;
- /* Traverse locks, blocks and shares of this file
- * and update file->f_locks count */
- if (nlm_inspect_file(data, file, match))
- ret = 1;
+ if (!is_failover_file || is_failover_file(data, file)) {
+ mutex_unlock(&nlm_file_mutex);
- mutex_lock(&nlm_file_mutex);
- file->f_count--;
- /* No more references to this file. Let go of it. */
- if (list_empty(&file->f_blocks) && !file->f_locks
- && !file->f_shares && !file->f_count) {
- hlist_del(&file->f_list);
- nlm_close_files(file);
- kfree(file);
+ if (nlm_inspect_file(data, file, match))
+ ret = 1;
+
+ mutex_lock(&nlm_file_mutex);
}
+
+ file->f_count--;
+ nlm_file_release(file);
+ file = next;
}
}
mutex_unlock(&nlm_file_mutex);