From d59729f4e794f814b25ccd2aebfbe606242c4544 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Sat, 30 Jul 2011 12:34:19 -0400 Subject: [PATCH] ext4: fix races in ext4_sync_parent() Fix problems if fsync() races against a rename of a parent directory as pointed out by Al Viro in his own inimitable way: >While we are at it, could somebody please explain what the hell is ext4 >doing in >static int ext4_sync_parent(struct inode *inode) >{ > struct writeback_control wbc; > struct dentry *dentry = NULL; > int ret = 0; > > while (inode && ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) { > ext4_clear_inode_state(inode, EXT4_STATE_NEWENTRY); > dentry = list_entry(inode->i_dentry.next, > struct dentry, d_alias); > if (!dentry || !dentry->d_parent || !dentry->d_parent->d_inode) > break; > inode = dentry->d_parent->d_inode; > ret = sync_mapping_buffers(inode->i_mapping); > ... >Note that dentry obviously can't be NULL there. dentry->d_parent is never >NULL. And dentry->d_parent would better not be negative, for crying out >loud! What's worse, there's no guarantees that dentry->d_parent will >remain our parent over that sync_mapping_buffers() *and* that inode won't >just be freed under us (after rename() and memory pressure leading to >eviction of what used to be our dentry->d_parent)...... Reported-by: Al Viro Signed-off-by: "Theodore Ts'o" --- fs/ext4/fsync.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c index ce66d2fe826c..f9dbe33cde5e 100644 --- a/fs/ext4/fsync.c +++ b/fs/ext4/fsync.c @@ -129,15 +129,30 @@ static int ext4_sync_parent(struct inode *inode) { struct writeback_control wbc; struct dentry *dentry = NULL; + struct inode *next; int ret = 0; - while (inode && ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) { + if (!ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) + return 0; + inode = igrab(inode); + while (ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) { ext4_clear_inode_state(inode, EXT4_STATE_NEWENTRY); - dentry = list_entry(inode->i_dentry.next, - struct dentry, d_alias); - if (!dentry || !dentry->d_parent || !dentry->d_parent->d_inode) + dentry = NULL; + spin_lock(&inode->i_lock); + if (!list_empty(&inode->i_dentry)) { + dentry = list_first_entry(&inode->i_dentry, + struct dentry, d_alias); + dget(dentry); + } + spin_unlock(&inode->i_lock); + if (!dentry) + break; + next = igrab(dentry->d_parent->d_inode); + dput(dentry); + if (!next) break; - inode = dentry->d_parent->d_inode; + iput(inode); + inode = next; ret = sync_mapping_buffers(inode->i_mapping); if (ret) break; @@ -148,6 +163,7 @@ static int ext4_sync_parent(struct inode *inode) if (ret) break; } + iput(inode); return ret; } -- 2.20.1