Re: [PATCH] reiserfs: fix race in readdir

[Jeff Mahoney <jeffm@suse.com>]

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On 4/2/14, 2:29 PM, Jan Kara wrote:
> On Wed 02-04-14 20:09:55, Jan Kara wrote:
>> On Wed 02-04-14 11:57:54, Jeff Mahoney wrote:
>>> jdm-20004 reiserfs_delete_xattrs: Couldn't delete all xattrs (-2)
>>>
>>> The -ENOENT is due to readdir calling dir_emit on the same entry twice.
>>>
>>> If the dir_emit callback sleeps and the tree is changed underneath us,
>>> we won't be able to trust deh_offset(deh) anymore. We need to save
>>> next_pos before we might sleep so we can find the next entry.
>>>
>>> This can also affect non-xattr users of readdir, though the race is tighter.
>>>
>>> Cc: <stable@vger.kernel.org> 
>>> Signed-off-by: Jeff Mahoney <jeffm@suse.com>
>>   The patch looks good to me so unless someone objects, I'll merge this
>> patch with Linus.
>   Umm, actually, what if dir_emit() returns error? Previously we tried
> again the same entry, now we continue with the next one. Is that intended?
> If yes, please comment on that in the changelog.

Sigh. Yes. You're right. I missed that part of the error handling.

- -Jeff


>>> ---
>>>  fs/reiserfs/dir.c |    9 +++++++--
>>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> --- a/fs/reiserfs/dir.c
>>> +++ b/fs/reiserfs/dir.c
>>> @@ -179,6 +179,13 @@ int reiserfs_readdir_inode(struct inode
>>>  				memcpy(local_buf, d_name, d_reclen);
>>>  
>>>  				/*
>>> +				 * deh_offset(deh) will be invalid if dir_emit
>>> +				 * sleeps. We need to know the offset after
>>> +				 * this one to continue.
>>> +				 */
>>> +				next_pos = deh_offset(deh) + 1;
>>> +
>>> +				/*
>>>  				 * Since filldir might sleep, we can release
>>>  				 * the write lock here for other waiters
>>>  				 */
>>> @@ -196,8 +203,6 @@ int reiserfs_readdir_inode(struct inode
>>>  				if (local_buf != small_buf) {
>>>  					kfree(local_buf);
>>>  				}
>>> -				// next entry should be looked for with such offset
>>> -				next_pos = deh_offset(deh) + 1;
>>>  
>>>  				if (item_moved(&tmp_ih, &path_to_entry)) {
>>>  					set_cpu_key_k_offset(&pos_key,
>>>
>>> -- 
>>> Jeff Mahoney
>>> SUSE Labs
>> -- 
>> Jan Kara <jack@suse.cz>
>> SUSE Labs, CR


- -- 
Jeff Mahoney
SUSE Labs
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