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, 9 insertions, 0 deletions

diff --git a/fs/fuse/xattr.c b/fs/fuse/xattr.c
index 371bdcbc7233..cdea18de94f7 100644
--- a/fs/fuse/xattr.c
+++ b/fs/fuse/xattr.c
@@ -113,6 +113,9 @@ ssize_t fuse_listxattr(struct dentry *entry, char *list, size_t size)
 	struct fuse_getxattr_out outarg;
 	ssize_t ret;
 
+	if (fuse_is_bad(inode))
+		return -EIO;
+
 	if (!fuse_allow_current_process(fm->fc))
 		return -EACCES;
 
@@ -178,6 +181,9 @@ static int fuse_xattr_get(const struct xattr_handler *handler,
 			 struct dentry *dentry, struct inode *inode,
 			 const char *name, void *value, size_t size)
 {
+	if (fuse_is_bad(inode))
+		return -EIO;
+
 	return fuse_getxattr(inode, name, value, size);
 }
 
@@ -186,6 +192,9 @@ static int fuse_xattr_set(const struct xattr_handler *handler,
 			  const char *name, const void *value, size_t size,
 			  int flags)
 {
+	if (fuse_is_bad(inode))
+		return -EIO;
+
 	if (!value)
 		return fuse_removexattr(inode, name);