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| author | Theodore Ts'o <tytso@mit.edu> | 2011-07-30 12:34:19 -0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2011-07-30 12:34:19 -0400 |
| commit | d59729f4e794f814b25ccd2aebfbe606242c4544 (patch) | |
| tree | 96b7cfef8124c23b6a17ded73fddffc567d6f2a1 | |
| parent | 29ae07b702cb77dbc24b0843f15ee8cf8a642311 (diff) | |
| download | linux-d59729f4e794f814b25ccd2aebfbe606242c4544.tar.bz2 | |
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 <viro@ZenIV.linux.org.uk>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
| -rw-r--r-- | fs/ext4/fsync.c | 26 |
1 files 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; } |