[PATCH 1/2] fuse: fix invalidate lock leak on setattr writeback failure

[Baokun Li <libaokun@linux.alibaba.com>]

fuse_do_setattr() takes filemap_invalidate_lock() for a DAX truncate
(fault_blocked = true) and releases it at the out:/error: labels.  But
when a writeback flush is also needed, a write_inode_now() failure
returns directly and leaks the lock, so any later fault or truncate on
the file stalls on the stale rwsem.

For example, truncate(2) on a setuid file reaches fuse_do_setattr()
with both ATTR_SIZE and ATTR_MODE set:

  truncate(2)
  └─ do_truncate()
     ├─ dentry_needs_remove_privs()         # S_ISUID
     └─ notify_change()                     # KILL_SUID -> ATTR_MODE
        └─ fuse_setattr()                   # no killpriv:
           │                                #   ia_valid |= ATTR_MODE
           └─ fuse_do_setattr()
              ├─ filemap_invalidate_lock()  # IS_DAX && is_truncate
              └─ write_inode_now()          # is_wb && ATTR_MODE
                 └─ if (err)                # e.g. daemon -> -EIO
                    return err              # <- lock leaked

Fix this by adding an unlock label that releases the lock before
returning the error, and use it for the fuse_dax_break_layouts()
failure path as well.

Fixes: 6ae330cad6ef ("virtiofs: serialize truncate/punch_hole and dax fault path")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: Baokun Li <libaokun@linux.alibaba.com>
---
 fs/fuse/dir.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 0e2a1039fa43..48763bc192f3 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -2161,10 +2161,8 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 		filemap_invalidate_lock(mapping);
 		fault_blocked = true;
 		err = fuse_dax_break_layouts(inode, 0, -1);
-		if (err) {
-			filemap_invalidate_unlock(mapping);
-			return err;
-		}
+		if (err)
+			goto unlock;
 	}
 
 	if (attr->ia_valid & ATTR_OPEN) {
@@ -2191,7 +2189,7 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 			 ATTR_TIMES_SET)) {
 		err = write_inode_now(inode, true);
 		if (err)
-			return err;
+			goto unlock;
 
 		fuse_set_nowrite(inode);
 		fuse_release_nowrite(inode);
@@ -2299,6 +2297,7 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 
 	clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
 
+unlock:
 	if (fault_blocked)
 		filemap_invalidate_unlock(mapping);
 	return err;
-- 
2.43.7