From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay3.corp.sgi.com [198.149.34.15]) by oss.sgi.com (Postfix) with ESMTP id 193047F4E for ; Mon, 15 Jun 2015 17:49:59 -0500 (CDT) Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by relay3.corp.sgi.com (Postfix) with ESMTP id 8B15CAC002 for ; Mon, 15 Jun 2015 15:49:58 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by cuda.sgi.com with ESMTP id hBvyU74QkAFYgTwc (version=TLSv1 cipher=AES256-SHA bits=256 verify=NO) for ; Mon, 15 Jun 2015 15:49:57 -0700 (PDT) Message-ID: <557F5693.30504@redhat.com> Date: Mon, 15 Jun 2015 17:49:55 -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> In-Reply-To: <20150615224710.GE10224@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 Cc: xfs-oss 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 B) I bet LTP doesn't do a remount to verify on-disk persistence C) ??? D) Profit! -Eric > Cheers, > > Dave. > _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs