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UBIFS: return error if link and unlink race 

Consider a scenario when 'vfs_link(dirA/fileA)' and
'vfs_unlink(dirA/fileA, dirB/fileB)' race. 'vfs_link()' does not
lock 'dirA->i_mutex', so this is possible. Both of the functions
lock 'fileA->i_mutex' though. Suppose 'vfs_unlink()' wins, and takes
'fileA->i_mutex' mutex first. Suppose 'fileA->i_nlink' is 1. In this
case 'ubifs_unlink()' will drop the last reference, and put 'inodeA'
to the list of orphans. After this, 'vfs_link()' will link
'dirB/fileB' to 'inodeA'. Thir is a problem because, for example,
the subsequent 'vfs_unlink(dirB/fileB)' will add the same inode
to the list of orphans.

This problem was reported by J. R. Okajima <hooanon05@yahoo.co.jp>

[Artem: add more comments, amended commit message]

Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
This commit is contained in:
Hunter Adrian 2009-05-14 06:32:30 +02:00 committed by Artem Bityutskiy
parent 6d6cb0d688
commit 8b3884a841
1 changed files with 19 additions and 0 deletions
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19
fs/ubifs/dir.c
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@ -528,6 +528,25 @@ static int ubifs_link(struct dentry *old_dentry, struct inode *dir,
inode->i_nlink, dir->i_ino);
ubifs_assert(mutex_is_locked(&dir->i_mutex));
ubifs_assert(mutex_is_locked(&inode->i_mutex));
/*
* Return -ENOENT if we've raced with unlink and i_nlink is 0. Doing
* otherwise has the potential to corrupt the orphan inode list.
*
* Indeed, consider a scenario when 'vfs_link(dirA/fileA)' and
* 'vfs_unlink(dirA/fileA, dirB/fileB)' race. 'vfs_link()' does not
* lock 'dirA->i_mutex', so this is possible. Both of the functions
* lock 'fileA->i_mutex' though. Suppose 'vfs_unlink()' wins, and takes
* 'fileA->i_mutex' mutex first. Suppose 'fileA->i_nlink' is 1. In this
* case 'ubifs_unlink()' will drop the last reference, and put 'inodeA'
* to the list of orphans. After this, 'vfs_link()' will link
* 'dirB/fileB' to 'inodeA'. This is a problem because, for example,
* the subsequent 'vfs_unlink(dirB/fileB)' will add the same inode
* to the list of orphans.
*/
if (inode->i_nlink == 0)
return -ENOENT;
err = dbg_check_synced_i_size(inode);
if (err)
return err;