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, 11 insertions, 8 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 349885353036..8cccecb55fb8 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -232,6 +232,9 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
 	bool dax_truncate = (file->f_flags & O_TRUNC) &&
 			  fc->atomic_o_trunc && FUSE_IS_DAX(inode);
 
+	if (fuse_is_bad(inode))
+		return -EIO;
+
 	err = generic_file_open(inode, file);
 	if (err)
 		return err;
@@ -469,7 +472,7 @@ static int fuse_flush(struct file *file, fl_owner_t id)
 	FUSE_ARGS(args);
 	int err;
 
-	if (is_bad_inode(inode))
+	if (fuse_is_bad(inode))
 		return -EIO;
 
 	err = write_inode_now(inode, 1);
@@ -541,7 +544,7 @@ static int fuse_fsync(struct file *file, loff_t start, loff_t end,
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	int err;
 
-	if (is_bad_inode(inode))
+	if (fuse_is_bad(inode))
 		return -EIO;
 
 	inode_lock(inode);
@@ -865,7 +868,7 @@ static int fuse_readpage(struct file *file, struct page *page)
 	int err;
 
 	err = -EIO;
-	if (is_bad_inode(inode))
+	if (fuse_is_bad(inode))
 		goto out;
 
 	err = fuse_do_readpage(file, page);
@@ -958,7 +961,7 @@ static void fuse_readahead(struct readahead_control *rac)
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	unsigned int i, max_pages, nr_pages = 0;
 
-	if (is_bad_inode(inode))
+	if (fuse_is_bad(inode))
 		return;
 
 	max_pages = min_t(unsigned int, fc->max_pages,
@@ -1570,7 +1573,7 @@ static ssize_t fuse_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	struct fuse_file *ff = file->private_data;
 	struct inode *inode = file_inode(file);
 
-	if (is_bad_inode(inode))
+	if (fuse_is_bad(inode))
 		return -EIO;
 
 	if (FUSE_IS_DAX(inode))
@@ -1588,7 +1591,7 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	struct fuse_file *ff = file->private_data;
 	struct inode *inode = file_inode(file);
 
-	if (is_bad_inode(inode))
+	if (fuse_is_bad(inode))
 		return -EIO;
 
 	if (FUSE_IS_DAX(inode))
@@ -2187,7 +2190,7 @@ static int fuse_writepages(struct address_space *mapping,
 	int err;
 
 	err = -EIO;
-	if (is_bad_inode(inode))
+	if (fuse_is_bad(inode))
 		goto out;
 
 	data.inode = inode;
@@ -2972,7 +2975,7 @@ long fuse_ioctl_common(struct file *file, unsigned int cmd,
 	if (!fuse_allow_current_process(fc))
 		return -EACCES;
 
-	if (is_bad_inode(inode))
+	if (fuse_is_bad(inode))
 		return -EIO;
 
 	return fuse_do_ioctl(file, cmd, arg, flags);