Re: [PATCH] xfs: Add check for unsupported xflags

Darrick J. Wong
2020-09-02T17:03:49Z

On Wed, Sep 02, 2020 at 01:11:00PM +0800, Xiao Yang wrote:
> 于 2020/9/2 12:10, Darrick J. Wong 写道:
> > On Wed, Sep 02, 2020 at 11:34:58AM +0800, Xiao Yang wrote:
> > > 于 2020/9/2 11:09, Darrick J. Wong 写道:
> > > > On Wed, Sep 02, 2020 at 10:41:11AM +0800, Xiao Yang wrote:
> > > > > On 2020/9/2 0:35, Darrick J. Wong wrote:
> > > > > > On Tue, Sep 01, 2020 at 02:05:53PM +0800, Xiao Yang wrote:
> > > > > > > On 2020/9/1 1:22, Darrick J. Wong wrote:
> > > > > > > > On Mon, Aug 31, 2020 at 09:37:45PM +0800, Xiao Yang wrote:
> > > > > > > > > Current ioctl(FSSETXATTR) ignores unsupported xflags silently
> > > > > > > > > so it it not clear for user to know unsupported xflags.
> > > > > > > Hi Darrick,
> > > > > > >
> > > > > > > Sorry for a typo(s/it it/it is/).
> > > > > > > > > For example, use ioctl(FSSETXATTR) to set dax flag on kernel
> > > > > > > > > v4.4 which doesn't support dax flag:
> > > > > > > > > --------------------------------
> > > > > > > > > # xfs_io -f -c "chattr +x" testfile;echo $?
> > > > > > > > > 0
> > > > > > > > > # xfs_io -c "lsattr" testfile
> > > > > > > > > ----------------X testfile
> > > > > > > > > --------------------------------
> > > > > > > > >
> > > > > > > > > Add check to report unsupported info as ioctl(SETXFLAGS) does.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Xiao Yang<yangx.jy@cn.fujitsu.com>
> > > > > > > > > ---
> > > > > > > > > fs/xfs/xfs_ioctl.c | 4 ++++
> > > > > > > > > include/uapi/linux/fs.h | 8 ++++++++
> > > > > > > > > 2 files changed, 12 insertions(+)
> > > > > > > > >
> > > > > > > > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> > > > > > > > > index 6f22a66777cd..cfe7f20c94fe 100644
> > > > > > > > > --- a/fs/xfs/xfs_ioctl.c
> > > > > > > > > +++ b/fs/xfs/xfs_ioctl.c
> > > > > > > > > @@ -1439,6 +1439,10 @@ xfs_ioctl_setattr(
> > > > > > > > >
> > > > > > > > > trace_xfs_ioctl_setattr(ip);
> > > > > > > > >
> > > > > > > > > + /* Check if fsx_xflags have unsupported xflags */
> > > > > > > > > + if (fa->fsx_xflags& ~FS_XFLAG_ALL)
> > > > > > > > > + return -EOPNOTSUPP;
> > > > > > > > Shouldn't this be in vfs_ioc_fssetxattr_check, since we're checking
> > > > > > > > against all the vfs defined XFLAGS?
> > > > > > > Right, different filesystems support different XFLAGS so I think it is hard
> > > > > > > to put this
> > > > > > > check into vfs_ioc_fssetxattr_check(). For example,
> > > > > > > 1) ext4 defines EXT4_SUPPORTED_FS_XFLAGS and do the check before
> > > > > > > vfs_ioc_fssetxattr_check():
> > > > > > I guess I wasn't clear enough about the xflags checks.
> > > > > >
> > > > > > Historically, XFS never checked the flags value for set bits that don't
> > > > > > correspond to a known (X)FS_XFLAG_ value. If your program passes in a
> > > > > > set bit that the kernel doesn't know about, the kernel does nothing
> > > > > > about it, and a subsequent FSGETXATTR will not have that bit set.
> > > > > Hi Darrick,
> > > > >
> > > > > Yes, we have to confirm if XFS supports the specified xflag by both
> > > > > FSSETXATTR and
> > > > > FSGETXATT(instead of the single FSSETXATTR) so it is not clear and simple
> > > > > for user.
> > > > > This patch just makes ioctl(FSSETXATTR) return -EOPNOTSUPP when XFS doesn't
> > > > > support
> > > > > the specified xflag.
> > > > > Note: ext4/f2fs/btrfs have implemented the behavior.
> > > > >
> > > > > BTW:
> > > > > With this patch, current '_require_xfs_io_command "chattr"' in xfstests can
> > > > > check XFS's
> > > > > supported xflags directly and don't need to check them by extra
> > > > > ioctl(FSGETXATTR).
> > > > > > The old ioctl (back when it was xfs only) wasn't officially documented,
> > > > > > so it wasn't clear whether the kernel should do that or return EINVAL.
> > > > > >
> > > > > > Then the ioctl pair was hoisted to the VFS, a manpage was written
> > > > > > specifying an EINVAL return for invalid arguments, and ext4, f2fs, and
> > > > > > btrfs followed this.
> > > > > >
> > > > > > FS_XFLAG_ALL is the set of all defined FS_XFLAG_* values. Therefore,
> > > > > > the VFS needs to check that userspace does not try to pass in a flags
> > > > > > value with totally unknown bits set in it. That's what I thought you
> > > > > > were trying to do with this patch.
> > > > > >
> > > > > > Since you bring it up, however -- ext4/f2fs/btrfs support only a subset
> > > > > > of the (X)FS_XFLAG values, so they implement a second check to constrain
> > > > > > the flags values to the ones that those filesystems support. I doubt
> > > > > > that the set of flags that XFS supports will stay the same as the set of
> > > > > > flags that the VFS header establishes, so it would be wise to implement
> > > > > > a second check in XFS, even if right now it provides no added benefit
> > > > > > over the VFS check.
> > > > > This patch just tries to implement the second check in XFS.
> > > > >
> > > > > Different filesystems(ext4/f2fs/btrfs/xfs) support different xflags so the
> > > > > check depends
> > > > > on these filesystems instead of vfs. I am not sure why we need to implement
> > > > > the first
> > > > > check?(I think the first check seems surplus)
> > Oops, sorry, I didn't notice this.
> >
> > The reason for checking both in the VFS and in the fs driver itself is
> > to ensure that there's at least some checking of the syscall inputs even
> > if a new fs implementation neglects to check the flags.
> Hi Darrick,
>
> It is reasonable for your concern to add a check in VFS, but checking all
> defined xflags is too rough in VFS if one filesystem only supports few
> xflags. :-)

I was advocating for two levels of flags checks: one in the VFS for
undefined flags, and a second check in each filesystem for whichever
flag it wants to recognize. I was not implying that the VFS checks
would be sufficient on their own.

--D

> Best Regards,
> Xiao Yang
> > (Or the original implementation<cough>.)
> >
> > > Hi Darrick,
> > >
> > > Do you agree this point that only implements the second check in XFS? :-)
> > Yes.
> >
> > > > > > IOWs, I'm suggesting that you write one patch to define a FS_XFLAG_ALL
> > > > > > consisting of all known FS_XFLAG_* values, and a check in
> > > > > > vfs_ioc_fssetxattr_check that uses that to establish basic sanity of the
> > > > > > arguments; and a second patch to define a XFS_XFLAG_ALL consisting of
> > > > > > all the flags that XFS supports, and a check in xfs_ioctl_setattr that
> > > > > > uses XFS_XFLAG_ALL to establish that we're not passing in an XFLAG that
> > > > > > XFS doesn't support.
> > > > > How about the following patch(i.e. add a check in xfs_ioctl_setattr):
> > > > > -----------------------------------------------------------
> > > > > diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
> > > > > index 84bcffa87753..8ac19f55c701 100644
> > > > > --- a/fs/xfs/libxfs/xfs_fs.h
> > > > > +++ b/fs/xfs/libxfs/xfs_fs.h
> > > > > @@ -92,6 +92,14 @@ struct getbmapx {
> > > > > #define XFS_FMR_OWN_COW FMR_OWNER('X', 7) /* cow staging */
> > > > > #define XFS_FMR_OWN_DEFECTIVE FMR_OWNER('X', 8) /* bad blocks */
> > > > >
> > > > > +#define XFS_SUPPORTED_FS_XFLAGS \
> > > > > + (FS_XFLAG_REALTIME | FS_XFLAG_PREALLOC | FS_XFLAG_IMMUTABLE | \
> > > > > + FS_XFLAG_APPEND | FS_XFLAG_SYNC | FS_XFLAG_NOATIME |
> > > > > FS_XFLAG_NODUMP | \
> > > > > + FS_XFLAG_RTINHERIT | FS_XFLAG_PROJINHERIT | FS_XFLAG_NOSYMLINKS | \
> > > > > + FS_XFLAG_EXTSIZE | FS_XFLAG_EXTSZINHERIT | FS_XFLAG_NODEFRAG | \
> > > > > + FS_XFLAG_FILESTREAM | FS_XFLAG_DAX | FS_XFLAG_COWEXTSIZE | \
> > > > > + FS_XFLAG_HASATTR)
> > > > This is an implementation detail, so you might as well put it right
> > > > above xfs_ioctl_setattr.
> > > >
> > > > That and xfs_fs.h gets packaged in /usr/include so we don't want to have
> > > > to support that symbol for userspace programs forever.
> > > Will put the macro above xfs_ioctl_setattr, as below:
> > > -------------------------------------------------------------
> > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> > > index 6f22a66777cd..e188e81961bd 100644
> > > --- a/fs/xfs/xfs_ioctl.c
> > > +++ b/fs/xfs/xfs_ioctl.c
> > > @@ -1425,6 +1425,14 @@ xfs_ioctl_setattr_check_projid(
> > > return 0;
> > > }
> > >
> > > +#define XFS_SUPPORTED_FS_XFLAGS \
> > > + (FS_XFLAG_REALTIME | FS_XFLAG_PREALLOC | FS_XFLAG_IMMUTABLE | \
> > > + FS_XFLAG_APPEND | FS_XFLAG_SYNC | FS_XFLAG_NOATIME | FS_XFLAG_NODUMP | \
> > > + FS_XFLAG_RTINHERIT | FS_XFLAG_PROJINHERIT | FS_XFLAG_NOSYMLINKS | \
> > > + FS_XFLAG_EXTSIZE | FS_XFLAG_EXTSZINHERIT | FS_XFLAG_NODEFRAG | \
> > > + FS_XFLAG_FILESTREAM | FS_XFLAG_DAX | FS_XFLAG_COWEXTSIZE | \
> > > + FS_XFLAG_HASATTR)
> > > +
> > > STATIC int
> > > xfs_ioctl_setattr(
> > > xfs_inode_t *ip,
> > > @@ -1439,6 +1447,10 @@ xfs_ioctl_setattr(
> > >
> > > trace_xfs_ioctl_setattr(ip);
> > >
> > > + /* Check if fsx_xflags has unsupported xflags */
> > > + if (fa->fsx_xflags& ~XFS_SUPPORTED_FS_XFLAGS)
> > > + return -EOPNOTSUPP;
> > > +
> > > code = xfs_ioctl_setattr_check_projid(ip, fa);
> > > if (code)
> > > return code;
> > > -------------------------------------------------------------
> > >
> > > Best Regards,
> > > Xiao Yang
> > > > --D
> > > >
> > > > > +
> > > > > /*
> > > > > * Structure for XFS_IOC_FSSETDM.
> > > > > * For use by backup and restore programs to set the XFS on-disk inode
> > > > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> > > > > index 6f22a66777cd..ec5feaa8dec8 100644
> > > > > --- a/fs/xfs/xfs_ioctl.c
> > > > > +++ b/fs/xfs/xfs_ioctl.c
> > > > > @@ -1439,6 +1439,10 @@ xfs_ioctl_setattr(
> > > > >
> > > > > trace_xfs_ioctl_setattr(ip);
> > > > >
> > > > > + /* Check if fsx_xflags have unsupported xflags */
> > > > > + if (fa->fsx_xflags& ~XFS_SUPPORTED_FS_XFLAGS)
> > > > > + return -EOPNOTSUPP;
> > > > > +
> > > > > code = xfs_ioctl_setattr_check_projid(ip, fa);
> > > > > if (code)
> > > > > return code;
> > > > > -----------------------------------------------------------
> > > > >
> > > > > Best Regards,
> > > > > Xiao Yang
> > > > > > --D
> > > > > >
> > > > > > > -------------------------------------------------------------------------------
> > > > > > > ext4/ioctl.c:
> > > > > > > #define EXT4_SUPPORTED_FS_XFLAGS (FS_XFLAG_SYNC | FS_XFLAG_IMMUTABLE | \
> > > > > > > FS_XFLAG_APPEND | FS_XFLAG_NODUMP | \
> > > > > > > FS_XFLAG_NOATIME | FS_XFLAG_PROJINHERIT |
> > > > > > > \
> > > > > > > FS_XFLAG_DAX)
> > > > > > > ...
> > > > > > > if (fa.fsx_xflags& ~EXT4_SUPPORTED_FS_XFLAGS)
> > > > > > > return -EOPNOTSUPP;
> > > > > > > ...
> > > > > > > -------------------------------------------------------------------------------
> > > > > > > 2) btrfs adds check_xflags() and calls it before vfs_ioc_fssetxattr_check():
> > > > > > > -------------------------------------------------------------------------------
> > > > > > > btrfs/ioctl.c:
> > > > > > > static int check_xflags(unsigned int flags)
> > > > > > > {
> > > > > > > if (flags& ~(FS_XFLAG_APPEND | FS_XFLAG_IMMUTABLE |
> > > > > > > FS_XFLAG_NOATIME |
> > > > > > > FS_XFLAG_NODUMP | FS_XFLAG_SYNC))
> > > > > > > return -EOPNOTSUPP;
> > > > > > > return 0;
> > > > > > > }
> > > > > > > ...
> > > > > > > ret = check_xflags(fa.fsx_xflags);
> > > > > > > if (ret)
> > > > > > > return ret;
> > > > > > > ...
> > > > > > > -------------------------------------------------------------------------------
> > > > > > >
> > > > > > > Perhaps, I should rename FS_XFLAG_ALL to XFS_SUPPORTED_FS_XFLAGS and move
> > > > > > > it into libxfs/xfs_fs.h.
> > > > > > >
> > > > > > > Best Regards,
> > > > > > > Xiao Yang
> > > > > > > > --D
> > > > > > > >
> > > > > > > > > +
> > > > > > > > > code = xfs_ioctl_setattr_check_projid(ip, fa);
> > > > > > > > > if (code)
> > > > > > > > > return code;
> > > > > > > > > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> > > > > > > > > index f44eb0a04afd..31b6856f6877 100644
> > > > > > > > > --- a/include/uapi/linux/fs.h
> > > > > > > > > +++ b/include/uapi/linux/fs.h
> > > > > > > > > @@ -142,6 +142,14 @@ struct fsxattr {
> > > > > > > > > #define FS_XFLAG_COWEXTSIZE 0x00010000 /* CoW extent size allocator hint */
> > > > > > > > > #define FS_XFLAG_HASATTR 0x80000000 /* no DIFLAG for this */
> > > > > > > > >
> > > > > > > > > +#define FS_XFLAG_ALL \
> > > > > > > > > + (FS_XFLAG_REALTIME | FS_XFLAG_PREALLOC | FS_XFLAG_IMMUTABLE | \
> > > > > > > > > + FS_XFLAG_APPEND | FS_XFLAG_SYNC | FS_XFLAG_NOATIME | FS_XFLAG_NODUMP | \
> > > > > > > > > + FS_XFLAG_RTINHERIT | FS_XFLAG_PROJINHERIT | FS_XFLAG_NOSYMLINKS | \
> > > > > > > > > + FS_XFLAG_EXTSIZE | FS_XFLAG_EXTSZINHERIT | FS_XFLAG_NODEFRAG | \
> > > > > > > > > + FS_XFLAG_FILESTREAM | FS_XFLAG_DAX | FS_XFLAG_COWEXTSIZE | \
> > > > > > > > > + FS_XFLAG_HASATTR)
> > > > > > > > > +
> > > > > > > > > /* the read-only stuff doesn't really belong here, but any other place is
> > > > > > > > > probably as bad and I don't want to create yet another include file. */
> > > > > > > > >
> > > > > > > > > --
> > > > > > > > > 2.25.1
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > .
> > > > > > > >
> > > > > > .
> > > > > >
> > > > >
> > > > .
> > > >
> > >
> > >
> >
> > .
> >
>
>
>