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>
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@ -528,6 +528,25 @@ static int ubifs_link(struct dentry *old_dentry, struct inode *dir,
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inode->i_nlink, dir->i_ino);
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inode->i_nlink, dir->i_ino);
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ubifs_assert(mutex_is_locked(&dir->i_mutex));
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ubifs_assert(mutex_is_locked(&dir->i_mutex));
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ubifs_assert(mutex_is_locked(&inode->i_mutex));
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ubifs_assert(mutex_is_locked(&inode->i_mutex));
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/*
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* Return -ENOENT if we've raced with unlink and i_nlink is 0. Doing
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* otherwise has the potential to corrupt the orphan inode list.
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*
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* Indeed, consider a scenario when 'vfs_link(dirA/fileA)' and
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* 'vfs_unlink(dirA/fileA, dirB/fileB)' race. 'vfs_link()' does not
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* lock 'dirA->i_mutex', so this is possible. Both of the functions
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* lock 'fileA->i_mutex' though. Suppose 'vfs_unlink()' wins, and takes
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* 'fileA->i_mutex' mutex first. Suppose 'fileA->i_nlink' is 1. In this
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* case 'ubifs_unlink()' will drop the last reference, and put 'inodeA'
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* to the list of orphans. After this, 'vfs_link()' will link
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* 'dirB/fileB' to 'inodeA'. This is a problem because, for example,
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* the subsequent 'vfs_unlink(dirB/fileB)' will add the same inode
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* to the list of orphans.
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*/
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if (inode->i_nlink == 0)
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return -ENOENT;
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err = dbg_check_synced_i_size(inode);
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err = dbg_check_synced_i_size(inode);
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if (err)
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if (err)
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return err;
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return err;
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