fuse: fix bad inode

Jan Kara's analysis of the syzbot report (edited):

  The reproducer opens a directory on FUSE filesystem, it then attaches
  dnotify mark to the open directory.  After that a fuse_do_getattr() call
  finds that attributes returned by the server are inconsistent, and calls
  make_bad_inode() which, among other things does:

          inode->i_mode = S_IFREG;

  This then confuses dnotify which doesn't tear down its structures
  properly and eventually crashes.

Avoid calling make_bad_inode() on a live inode: switch to a private flag on
the fuse inode.  Also add the test to ops which the bad_inode_ops would
have caught.

This bug goes back to the initial merge of fuse in 2.6.14...

Reported-by: syzbot+f427adf9324b92652ccc@syzkaller.appspotmail.com
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Tested-by: Jan Kara <jack@suse.cz>
Cc: <stable@vger.kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/fuse/acl.c b/fs/fuse/acl.c
index 5a48cee6d7d3..f529075a2ce8 100644
--- a/fs/fuse/acl.c
+++ b/fs/fuse/acl.c
@@ -19,6 +19,9 @@ struct posix_acl *fuse_get_acl(struct inode *inode, int type)
 	void *value = NULL;
 	struct posix_acl *acl;
 
+	if (fuse_is_bad(inode))
+		return ERR_PTR(-EIO);
+
 	if (!fc->posix_acl || fc->no_getxattr)
 		return NULL;
 
@@ -53,6 +56,9 @@ int fuse_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 	const char *name;
 	int ret;
 
+	if (fuse_is_bad(inode))
+		return -EIO;
+
 	if (!fc->posix_acl || fc->no_setxattr)
 		return -EOPNOTSUPP;