From 8b3884a841f398f6e0a0411d6929d8d9381bb265 Mon Sep 17 00:00:00 2001 From: Hunter Adrian Date: Thu, 14 May 2009 06:32:30 +0200 Subject: [PATCH] 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 [Artem: add more comments, amended commit message] Signed-off-by: Adrian Hunter Signed-off-by: Artem Bityutskiy --- fs/ubifs/dir.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c index f55d523c52b..552fb0111ff 100644 --- a/fs/ubifs/dir.c +++ b/fs/ubifs/dir.c @@ -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;