On Mon, May 24, 2021 at 02:21:15PM -0400, Brian Foster wrote:
> On Mon, May 24, 2021 at 10:23:28AM -0700, Darrick J. Wong wrote:
> > On Mon, May 24, 2021 at 06:42:28AM -0400, Brian Foster wrote:
> > > On Sun, May 23, 2021 at 06:01:25PM -0700, Darrick J. Wong wrote:
> > > > From: Darrick J. Wong <djwong@xxxxxxxxxx>
> > > >
> > > > The RTINHERIT bit can be set on a directory so that newly created
> > > > regular files will have the REALTIME bit set to store their data on the
> > > > realtime volume. If an extent size hint (and EXTSZINHERIT) are set on
> > > > the directory, the hint will also be copied into the new file.
> > > >
> > > > As pointed out in previous patches, for realtime files we require the
> > > > extent size hint be an integer multiple of the realtime extent, but we
> > > > don't perform the same validation on a directory with both RTINHERIT and
> > > > EXTSZINHERIT set, even though the only use-case of that combination is
> > > > to propagate extent size hints into new realtime files. This leads to
> > > > inode corruption errors when the bad values are propagated.
> > > >
> > > > Because there may be existing filesystems with such a configuration, we
> > > > cannot simply amend the inode verifier to trip on these directories and
> > > > call it a day because that will cause previously "working" filesystems
> > > > to start throwing errors abruptly. Note that it's valid to have
> > > > directories with rtinherit set even if there is no realtime volume, in
> > > > which case the problem does not manifest because rtinherit is ignored if
> > > > there's no realtime device; and it's possible that someone set the flag,
> > > > crashed, repaired the filesystem (which clears the hint on the realtime
> > > > file) and continued.
> > > >
> > > > Therefore, mitigate this issue in several ways: First, if we try to
> > > > write out an inode with both rtinherit/extszinherit set and an unaligned
> > > > extent size hint, we'll simply turn off the hint to correct the error.
> > > > Second, if someone tries to misconfigure a file via the fssetxattr
> > > > ioctl, we'll fail the ioctl. Third, we reverify both extent size hint
> > > > values when we propagate heritable inode attributes from parent to
> > > > child, so that we prevent misconfigurations from spreading.
> > > >
> > > > Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> > > > ---
> > > > fs/xfs/libxfs/xfs_inode_buf.c | 13 +++++++++++++
> > > > fs/xfs/libxfs/xfs_trans_inode.c | 15 +++++++++++++++
> > > > fs/xfs/xfs_inode.c | 29 +++++++++++++++++++++++++++++
> > > > fs/xfs/xfs_ioctl.c | 15 +++++++++++++++
> > > > 4 files changed, 72 insertions(+)
> > > >
> > > >
> > > > diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> > > > index 045118c7bf78..23c19e632c2d 100644
> > > > --- a/fs/xfs/libxfs/xfs_inode_buf.c
> > > > +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> > > > @@ -589,6 +589,19 @@ xfs_inode_validate_extsize(
> > > > inherit_flag = (flags & XFS_DIFLAG_EXTSZINHERIT);
> > > > extsize_bytes = XFS_FSB_TO_B(mp, extsize);
> > > >
> > > > + /*
> > > > + * This comment describes a historic gap in this verifier function.
> > > > + * On older kernels, XFS doesnt't check that the extent size hint is
> > > > + * an integer multiple of the rt extent size on a directory with both
> > > > + * RTINHERIT and EXTSZINHERIT flags set. This results in corruption
> > > > + * shutdowns when the misaligned hint propagates into new realtime
> > > > + * files, since they do check the rextsize alignment of the hint for
> > > > + * files with the REALTIME flag set. There could be filesystems with
> > > > + * misconfigured directories in the wild, so we cannot add it to the
> > > > + * verifier now because that would cause new corruption shutdowns on
> > > > + * the directories.
> > > > + */
> > > > +
> > >
> > > One of the things that confused me about the previous version is whether
> > > the verifier changes would have triggered corruption on read of a
> > > misconfigured inode.
> >
> > Yes, it would have, so I switched strategies...
> >
> > > If so, that seems to conflict with propagation
> > > mitigation if we can't read such a pre-existing inode in the first
> > > place. Is that not still a factor here too?
> >
> > ...completely away from making any code changes to the verifier.
> > So to answer your question, it should not be a factor any more.
> >
>
> Right.. what I mean to ask is whether it's worth mentioning in the
> comment we're adding here. ISTM it is, because the flag mitigation
> strategy depends on being able to actually read the historically broken
> inodes. At the very least, that tells somebody who might be cleverly
> trying to get around the caveat in the comment that they might need to
> consider the external code when making changes to the verifier.
<nod> This whole thing
>
> > > > if (rt_flag)
> > > > blocksize_bytes = mp->m_sb.sb_rextsize << mp->m_sb.sb_blocklog;
> > > > else
> > > > diff --git a/fs/xfs/libxfs/xfs_trans_inode.c b/fs/xfs/libxfs/xfs_trans_inode.c
> > > > index 78324e043e25..325f2dceec13 100644
> > > > --- a/fs/xfs/libxfs/xfs_trans_inode.c
> > > > +++ b/fs/xfs/libxfs/xfs_trans_inode.c
> > > > @@ -142,6 +142,21 @@ xfs_trans_log_inode(
> > > > flags |= XFS_ILOG_CORE;
> > > > }
> > > >
> > > > + /*
> > > > + * Inode verifiers on older kernels don't check that the extent size
> > > > + * hint is an integer multiple of the rt extent size on a directory
> > > > + * with both rtinherit and extszinherit flags set. If we're logging a
> > > > + * directory that is misconfigured in this way, clear the hint.
> > > > + */
> > > > + if ((ip->i_diflags & XFS_DIFLAG_RTINHERIT) &&
> > > > + (ip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) &&
> > > > + (ip->i_extsize % ip->i_mount->m_sb.sb_rextsize) > 0) {
> > > > + ip->i_diflags &= ~(XFS_DIFLAG_EXTSIZE |
> > > > + XFS_DIFLAG_EXTSZINHERIT);
> > > > + ip->i_extsize = 0;
> > > > + flags |= XFS_ILOG_CORE;
> > > > + }
> > > > +
> > >
> > > Hmm.. if we're going to also clear the state from preexisting
> > > directories (vs. just mitigate propagation), it kind of makes me wonder
> > > why we wouldn't just clear the bad settings from in-core inodes on read.
> >
> > Making corrections at iget time is complicated -- of the callers that
> > pass in a transaction, I'd would have to check every call site carefully
> > to ensure that we don't cancel what would otherwise be a clean
> > transaction, since that would lead to a shutdown. The non-transaction
> > iget callsites would each have to grow a call to get a transaction,
> > update the inode, and commit it. We'd have to be careful to make sure
> > that all new iget callsites do this properly, forever. We could make
> > the change nontransactionally and wait for someone to log the icore to
> > persist the changes, but that's always frowned upon.
> >
>
> The latter is more what I had in mind.. just filter out the bad state
> in-core (perhaps with a one-shot warning to let the user know this fs
> has the oddity) and let further modifications commit the change or not.
> I agree that it's probably overkill to introduce a transaction to
> persist a fix at read time where one does not already exist. But if
> we're going to silently modify what's on-disk anyways, I'm not sure I
> see a major problem with clearing it on read if it otherwise results in
> the same behavior. I believe we used to convert old (v1) inodes to v2 in
> a similar manner when read off disk into the in-core structure.
>
> FWIW, the reason I ask in this case is just to see if we can achieve the
> same desired behavior with less code. This seems like quite a rare case,
> so I think it would be a slightly unfortunate to have code spread in
> various places, including a non-trivial comment in the verifier, for
> something that could potentially be isolated to a single bit of
> filtering logic at or near the read verifier. Of course if I'm mistaken
> about the potential simplification, then I don't have any major issue
> with what the patch is currently doing..
Agreed that all of this would be a lot less complex if I modified
xfs_iget to detect and zero out the hint (without bothering to schedule
a transaction to commit it), but I tried setting DIFLAG2_BIGTIME in one
of the earlier y2038+ patchset revisions and caught criticism for
making the incore state inconsistent with the ondisk state. I think
that's why all the inode upgrades and whatnot end up in
xfs_trans_log_inode, because they're effectively free there.
>
> > That's why I decided to go with making updates in xfs_trans_log_inode,
> > since (a) it's not going to burn a bunch of human time, (b) it's where
> > we perform other silent inode upgrades, and (c) it doesn't generate any
> > new log traffic.
> >
> > However, I just had a thought--
> >
> > This patch doesn't do anything to fix the case of existing realtime
> > regular files with an invalid hint. The only time the invalid hint
> > actually bites us is in xfs_bmap_rtalloc. To fix that case, all I need
> > to do is amend xfs_trans_log_inode to fix realtime files too, and then
> > update xfs_bmap_rtalloc:
> >
> > align = xfs_get_extsz_hint(ap->ip);
> >
> > to check for bad hints:
> >
> > align = xfs_get_extsz_hint(ap->ip);
> > if (align > mp->m_sb.sb_rextsize &&
> > align % mp->m_sb.sb_rextsize)
> > align = mp->m_sb.sb_rextsize;
> >
> > If the allocation succeeds, then the rt file's inode (which is already
> > ijoined) gets logged, at which point we'll correct the inode.
> >
>
> Hmm.. that sounds reasonable in principle, but it's not clear to me if
> you mean to combine that with the explicit propagation prevention or use
> it in place of it. As above, I'm still curious if the implementation for
> this behavior needs to be more involved than 1. prevent new bad
> configurations in the ioctl path and 2. filter out the pre-existing bad
> settings at read time and let them persist naturally.
>
> Also if this is already more than likely a fatal error, I don't think
> I'd object to just letting the verifier fail and fixing the problem via
> repair (or filtering the verifier failure to the case where failure was
> otherwise imminent; the historical situation is a little unclear to me
> tbh).
AFAICT from spelunking the source code, the extent size verification
code has enforced (extsize % rextsize)==0 for realtime files since the
beginning of git, but has never enforced that for propagation from a
directory.
So while it's /really/ tempting to classify this an edge case (realtime)
of an edge case (rextsize > 1) of an edge case (rtinherit and
extszinherit both set) and break the old filesystems, I'm not
comfortable with breaking existing users. I'll certainly post an
xfs_repair patch to flag and clear these directories, however.
--D
>
> Brian
>
> > > Wouldn't that also prevent the state from propagating and/or clear it
> > > from directories on next modification?
> >
> > Yes, but with the reviewer costs mentioned above.
> >
> > --D
> >
> > >
> > > Brian
> > >
> > > > /*
> > > > * Record the specific change for fdatasync optimisation. This allows
> > > > * fdatasync to skip log forces for inodes that are only timestamp
> > > > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > > > index 0369eb22c1bb..e4c2da4566f1 100644
> > > > --- a/fs/xfs/xfs_inode.c
> > > > +++ b/fs/xfs/xfs_inode.c
> > > > @@ -690,6 +690,7 @@ xfs_inode_inherit_flags(
> > > > const struct xfs_inode *pip)
> > > > {
> > > > unsigned int di_flags = 0;
> > > > + xfs_failaddr_t failaddr;
> > > > umode_t mode = VFS_I(ip)->i_mode;
> > > >
> > > > if (S_ISDIR(mode)) {
> > > > @@ -729,6 +730,24 @@ xfs_inode_inherit_flags(
> > > > di_flags |= XFS_DIFLAG_FILESTREAM;
> > > >
> > > > ip->i_diflags |= di_flags;
> > > > +
> > > > + /*
> > > > + * Inode verifiers on older kernels only check that the extent size
> > > > + * hint is an integer multiple of the rt extent size on realtime files.
> > > > + * They did not check the hint alignment on a directory with both
> > > > + * rtinherit and extszinherit flags set. If the misaligned hint is
> > > > + * propagated from a directory into a new realtime file, new file
> > > > + * allocations will fail due to math errors in the rt allocator and/or
> > > > + * trip the verifiers. Validate the hint settings in the new file so
> > > > + * that we don't let broken hints propagate.
> > > > + */
> > > > + failaddr = xfs_inode_validate_extsize(ip->i_mount, ip->i_extsize,
> > > > + VFS_I(ip)->i_mode, ip->i_diflags);
> > > > + if (failaddr) {
> > > > + ip->i_diflags &= ~(XFS_DIFLAG_EXTSIZE |
> > > > + XFS_DIFLAG_EXTSZINHERIT);
> > > > + ip->i_extsize = 0;
> > > > + }
> > > > }
> > > >
> > > > /* Propagate di_flags2 from a parent inode to a child inode. */
> > > > @@ -737,12 +756,22 @@ xfs_inode_inherit_flags2(
> > > > struct xfs_inode *ip,
> > > > const struct xfs_inode *pip)
> > > > {
> > > > + xfs_failaddr_t failaddr;
> > > > +
> > > > if (pip->i_diflags2 & XFS_DIFLAG2_COWEXTSIZE) {
> > > > ip->i_diflags2 |= XFS_DIFLAG2_COWEXTSIZE;
> > > > ip->i_cowextsize = pip->i_cowextsize;
> > > > }
> > > > if (pip->i_diflags2 & XFS_DIFLAG2_DAX)
> > > > ip->i_diflags2 |= XFS_DIFLAG2_DAX;
> > > > +
> > > > + /* Don't let invalid cowextsize hints propagate. */
> > > > + failaddr = xfs_inode_validate_cowextsize(ip->i_mount, ip->i_cowextsize,
> > > > + VFS_I(ip)->i_mode, ip->i_diflags, ip->i_diflags2);
> > > > + if (failaddr) {
> > > > + ip->i_diflags2 &= ~XFS_DIFLAG2_COWEXTSIZE;
> > > > + ip->i_cowextsize = 0;
> > > > + }
> > > > }
> > > >
> > > > /*
> > > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> > > > index 6407921aca96..1fe4c1fc0aea 100644
> > > > --- a/fs/xfs/xfs_ioctl.c
> > > > +++ b/fs/xfs/xfs_ioctl.c
> > > > @@ -1291,6 +1291,21 @@ xfs_ioctl_setattr_check_extsize(
> > > >
> > > > new_diflags = xfs_flags2diflags(ip, fa->fsx_xflags);
> > > >
> > > > + /*
> > > > + * Inode verifiers on older kernels don't check that the extent size
> > > > + * hint is an integer multiple of the rt extent size on a directory
> > > > + * with both rtinherit and extszinherit flags set. Don't let sysadmins
> > > > + * misconfigure directories.
> > > > + */
> > > > + if ((new_diflags & XFS_DIFLAG_RTINHERIT) &&
> > > > + (new_diflags & XFS_DIFLAG_EXTSZINHERIT)) {
> > > > + unsigned int rtextsize_bytes;
> > > > +
> > > > + rtextsize_bytes = XFS_FSB_TO_B(mp, mp->m_sb.sb_rextsize);
> > > > + if (fa->fsx_extsize % rtextsize_bytes)
> > > > + return -EINVAL;
> > > > + }
> > > > +
> > > > failaddr = xfs_inode_validate_extsize(ip->i_mount,
> > > > XFS_B_TO_FSB(mp, fa->fsx_extsize),
> > > > VFS_I(ip)->i_mode, new_diflags);
> > > >
> > >
> >
>
