Re: [PATCH] check name_len before down_read xattr_sem and sb_read in ext2_xattr_get

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



2010/7/22 Jan Kara <jack@xxxxxxx>:
>> Hi,
>>        I walked through ext2_xattr_get, and felt that we can
>> do some optimization on it. For name_len check, it's done
>> after down xattr_sem and sb_read, both of which are time
>> consuming operation compared with strlen:
>>          down_read(&EXT2_I(inode)->xattr_sem);
>>  ...
>>          bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);
>>  ...
>>          /* find named attribute */
>>          name_len = strlen(name);
>>
>>          error = -ERANGE;
>>          if (name_len > 255)
>>                  goto cleanup;
>>
>>        Most of the case, you'll get one valid block, but if the
>> name len > 255, then the xattr_sem down and sb_bread operation
>> can be seen as a waste of time. So I think we'd better do
>> name len check as early as possible.
>>        Following is my patch, and it's against 2.6.35-rc4.
>> Please check it.
>>
>> Signed-off-by: Wang Sheng-Hui <crosslonelyover@xxxxxxxxx>
>> ---
>>  fs/ext2/xattr.c |   12 +++++++-----
>>  1 files changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
>> index 7c39157..0b94d61 100644
>> --- a/fs/ext2/xattr.c
>> +++ b/fs/ext2/xattr.c
>> @@ -161,6 +161,13 @@ ext2_xattr_get(struct inode *inode, int name_index, const char *name,
>>
>>       if (name == NULL)
>>               return -EINVAL;
>> +
>> +     /* find named attribute */
>> +     name_len = strlen(name);
>> +     error = -ERANGE;
>> +     if (name_len > 255)
>> +             goto cleanup;
>  But you cannot go to cleanup here because you don't hold xattr_sem...
>

Sorry, I'm a little confused by your words.
The patch just checks name_len, and it
doesn't need xattr_sem.



-- 


Thanks and Best Regards,
shenghui
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Reiser Filesystem Development]     [Ceph FS]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux FS]     [Yosemite National Park]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Device Mapper]     [Linux Media]

  Powered by Linux