Commit c7df4a1e authored Nov 11, 2019 by Theodore Ts'o

ext4: work around deleting a file with i_nlink == 0 safely

If the file system is corrupted such that a file's i_links_count is
too small, then it's possible that when unlinking that file, i_nlink
will already be zero.  Previously we were working around this kind of
corruption by forcing i_nlink to one; but we were doing this before
trying to delete the directory entry --- and if the file system is
corrupted enough that ext4_delete_entry() fails, then we exit with
i_nlink elevated, and this causes the orphan inode list handling to be
FUBAR'ed, such that when we unmount the file system, the orphan inode
list can get corrupted.

A better way to fix this is to simply skip trying to call drop_nlink()
if i_nlink is already zero, thus moving the check to the place where
it makes the most sense.

https://bugzilla.kernel.org/show_bug.cgi?id=205433

Link: https://lore.kernel.org/r/20191112032903.8828-1-tytso@mit.edu


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Reviewed-by: Andreas Dilger <adilger@dilger.ca>

parent 4ea99936

fs/ext4/namei.c

+5 −6

Original line number	Diff line number	Diff line
		@@ -3196,17 +3196,16 @@ static int ext4_unlink(struct inode dir, struct dentry dentry)
		if (IS_DIRSYNC(dir))
		ext4_handle_sync(handle);

		if (inode->i_nlink == 0) {
		ext4_warning_inode(inode, "Deleting file '%.*s' with no links",
		dentry->d_name.len, dentry->d_name.name);
		set_nlink(inode, 1);
		}
		retval = ext4_delete_entry(handle, dir, de, bh);
		if (retval)
		goto end_unlink;
		dir->i_ctime = dir->i_mtime = current_time(dir);
		ext4_update_dx_flag(dir);
		ext4_mark_inode_dirty(handle, dir);
		if (inode->i_nlink == 0)
		ext4_warning_inode(inode, "Deleting file '%.*s' with no links",
		dentry->d_name.len, dentry->d_name.name);
		else
		drop_nlink(inode);
		if (!inode->i_nlink)
		ext4_orphan_add(handle, inode);

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