From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay2.corp.sgi.com [137.38.102.29]) by oss.sgi.com (Postfix) with ESMTP id 7DEDC7F4E for ; Mon, 15 Jun 2015 20:26:51 -0500 (CDT) Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by relay2.corp.sgi.com (Postfix) with ESMTP id 55BC5304043 for ; Mon, 15 Jun 2015 18:26:47 -0700 (PDT) Received: from sandeen.net (sandeen.net [63.231.237.45]) by cuda.sgi.com with ESMTP id dKvVrL4ZRNHleS2b for ; Mon, 15 Jun 2015 18:26:45 -0700 (PDT) Message-ID: <557F7B54.7090500@sandeen.net> Date: Mon, 15 Jun 2015 20:26:44 -0500 From: Eric Sandeen MIME-Version: 1.0 Subject: Re: [PATCH] xfs: fix remote symlinks on V5/CRC filesystems References: <557F4E1E.8000505@redhat.com> <20150615222157.GD10224@dastard> <557F532F.9060505@redhat.com> <20150615224710.GE10224@dastard> <557F5693.30504@redhat.com> <20150615231623.GF10224@dastard> In-Reply-To: <20150615231623.GF10224@dastard> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Dave Chinner , Eric Sandeen Cc: xfs-oss On 6/15/15 6:16 PM, Dave Chinner wrote: > On Mon, Jun 15, 2015 at 05:49:55PM -0500, Eric Sandeen wrote: >> On 6/15/15 5:47 PM, Dave Chinner wrote: >>> On Mon, Jun 15, 2015 at 05:35:27PM -0500, Eric Sandeen wrote: >>>> On 6/15/15 5:21 PM, Dave Chinner wrote: >>>>> On Mon, Jun 15, 2015 at 05:13:50PM -0500, Eric Sandeen wrote: >>>>>> If we create a CRC filesystem, mount it, and create a symlink with >>>>>> a path long enough that it can't live in the inode, we get a very >>>>>> strange result upon remount: >>>>>> >>>>>> # ls -l mnt >>>>>> total 4 >>>>>> lrwxrwxrwx. 1 root root 929 Jun 15 16:58 link -> XSLM >>>>>> >>>>>> XSLM is the V5 symlink block header magic (which happens to be >>>>>> followed by a NUL, so the string looks terminated). >>>>>> >>>>>> xfs_readlink_bmap() advanced cur_chunk by the size of the header >>>>>> for CRC filesystems, but never actually used that pointer; it >>>>>> kept reading from bp->b_addr, which is the start of the block, >>>>>> rather than the start of the symlink data after the header. >>>>>> >>>>>> Looks like this problem goes back to v3.10. >>>>>> >>>>>> Fixing this gets us reading the proper link target, again. >>>>>> >>>>>> Signed-off-by: Eric Sandeen >>>>>> Cc: stable@vger.kernel.org >>>>>> --- >>>>>> >>>>>> diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c >>>>>> index 3df411e..40c0765 100644 >>>>>> --- a/fs/xfs/xfs_symlink.c >>>>>> +++ b/fs/xfs/xfs_symlink.c >>>>>> @@ -104,7 +104,7 @@ xfs_readlink_bmap( >>>>>> cur_chunk += sizeof(struct xfs_dsymlink_hdr); >>>>>> } >>>>>> >>>>>> - memcpy(link + offset, bp->b_addr, byte_cnt); >>>>>> + memcpy(link + offset, cur_chunk, byte_cnt); >>>>>> >>>>>> pathlen -= byte_cnt; >>>>>> offset += byte_cnt; >>>>> >>>>> Looks like the correct fix, so: >>>>> >>>>> Reviewed-by: Dave Chinner >>>>> >>>>> However, it raises a more disturbing question: how did we not trip >>>>> over this until now? I though we had long symlink test coverage in >>>>> xfstests but clearly we haven't - do you have a test that closes >>>>> this verification hole? >>>> >>>> It was a smaller part of a larger test harness I was using with xfs_metadump, >>>> which was trying to create every type of on-disk metadata. However, even with >>>> that I only stumbled on it, because I was only verifying that the results were >>>> uncorrupted and consistent with the original, not actually verifying that >>>> what I created was still there (on the original!) >>>> >>>> So, I don't have a test specific to this, no, but could certainly write one; >>>> I suppose a quick targeted fstest for just this bug would be ok, although >>>> a test w/ broader scope might make sense too. >>> >>> Sure, the metadump test is a good idea, but my question is more >>> asking why our broader tests haven't already covered verifying >>> MAXPATHLEN symlinks work correctly or not. Surely symlink >>> correctness is verified *somewhere* (even outside xfstests, >>> e.g. LTP?), and if so why haven't we seen this before now? If not, >>> then I'd suggest we've just uncovered a potential Nest O' Bugs... >> >> A) CRCs aren't default > > Yet many people have been testing them and putting them in > production (e.g. SLES 12), so they *should* have been tested. > >> B) I bet LTP doesn't do a remount to verify on-disk persistence > > Just reading back the symlink should expose the bug, right? > Or is it being hidden by the dentry cache or something else? it does seem to be cached, yes. -Eric > Cheers, > > Dave. > _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs