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

[ Upstream commit c7df4a1ecb8579838ec8c56b2bb6a6716e974f37 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: I9a08356694b4ef9823e9c8c417fa4a1a3fab4cdb
This commit is contained in:
Theodore Ts'o 2019-11-11 22:18:13 -05:00 committed by L R
parent 14185607f8
commit ae2ae2b6c2
1 changed files with 6 additions and 7 deletions
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13
fs/ext4/namei.c
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@ -2797,19 +2797,18 @@ static int ext4_unlink(struct inode *dir, struct dentry *dentry)
if (IS_DIRSYNC(dir))
ext4_handle_sync(handle);
if (!inode->i_nlink) {
ext4_warning(inode->i_sb,
"Deleting nonexistent file (%lu), %d",
inode->i_ino, inode->i_nlink);
set_nlink(inode, 1);
}
retval = ext4_delete_entry(handle, dir, de, bh);
if (retval)
goto end_unlink;
dir->i_ctime = dir->i_mtime = ext4_current_time(dir);
ext4_update_dx_flag(dir);
ext4_mark_inode_dirty(handle, dir);
drop_nlink(inode);
if (!inode->i_nlink)
ext4_warning(inode->i_sb,
"Deleting nonexistent file (%lu), %d",
inode->i_ino, inode->i_nlink);
else
drop_nlink(inode);
if (!inode->i_nlink)
ext4_orphan_add(handle, inode);
inode->i_ctime = ext4_current_time(inode);