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ext4: fix races in ext4_sync_parent()

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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 <viro@ZenIV.linux.org.uk>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2011-07-30 12:34:19 -04:00
parent 29ae07b702
commit d59729f4e7
1 changed files with 21 additions and 5 deletions
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26
fs/ext4/fsync.c
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@ -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;
inode = dentry->d_parent->d_inode;
next = igrab(dentry->d_parent->d_inode);
dput(dentry);
if (!next)
break;
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;
}