diff mbox series

quota: widen timestamps for the fs_disk_quota structure

Message ID 20200904053931.GB6096@magnolia
State Superseded
Headers show
Series quota: widen timestamps for the fs_disk_quota structure | expand

Commit Message

Darrick J. Wong Sept. 4, 2020, 5:39 a.m. UTC
From: Darrick J. Wong <darrick.wong@oracle.com>

Widen the timestamp fields in struct fs_disk_quota to handle quota grace
expiration times beyond 2038.  Since the only filesystem that's going to
use this (XFS) only supports unsigned 34-bit quantities, adding an extra
5 bits here should work fine.  We can rev the structure again in 350
years.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/quota/quota.c               |   40 +++++++++++++++++++++++++++++++++++++---
 include/uapi/linux/dqblk_xfs.h |   13 +++++++++++--
 2 files changed, 48 insertions(+), 5 deletions(-)

Comments

Jan Kara Sept. 4, 2020, 8:31 a.m. UTC | #1
On Thu 03-09-20 22:39:31, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Widen the timestamp fields in struct fs_disk_quota to handle quota grace
> expiration times beyond 2038.  Since the only filesystem that's going to
> use this (XFS) only supports unsigned 34-bit quantities, adding an extra
> 5 bits here should work fine.  We can rev the structure again in 350
> years.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Some comments below...

> @@ -588,10 +600,27 @@ static int quota_setxquota(struct super_block *sb, int type, qid_t id,
>  	return sb->s_qcop->set_dqblk(sb, qid, &qdq);
>  }
>  
> +static inline __s8 copy_to_xfs_dqblk_ts(const struct fs_disk_quota *d,
> +		__s32 *timer_lo, s64 timer)
> +{
> +	*timer_lo = timer;
> +	if (d->d_fieldmask & FS_DQ_BIGTIME)
> +		return timer >> 32;
> +	return 0;
> +}

Hum, this function API looks a bit strange to me - directly store timer_lo
and just return timer_hi... Why not having timer_hi as another function
argument?

> @@ -606,6 +635,10 @@ static void copy_to_xfs_dqblk(struct fs_disk_quota *dst, struct qc_dqblk *src,
>  	dst->d_ino_softlimit = src->d_ino_softlimit;
>  	dst->d_bcount = quota_btobb(src->d_space);
>  	dst->d_icount = src->d_ino_count;
> +	dst->d_itimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_itimer,
> +						src->d_ino_timer);
> +	dst->d_btimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_btimer,
> +						src->d_spc_timer);
>  	dst->d_itimer = src->d_ino_timer;
>  	dst->d_btimer = src->d_spc_timer;

Also it seems pointless (if not outright buggy due to sign-extension rules)
to store to say d_itimer when copy_to_xfs_dqblk_ts() already did it...

>  	dst->d_iwarns = src->d_ino_warns;
> @@ -613,7 +646,8 @@ static void copy_to_xfs_dqblk(struct fs_disk_quota *dst, struct qc_dqblk *src,
>  	dst->d_rtb_hardlimit = quota_btobb(src->d_rt_spc_hardlimit);
>  	dst->d_rtb_softlimit = quota_btobb(src->d_rt_spc_softlimit);
>  	dst->d_rtbcount = quota_btobb(src->d_rt_space);
> -	dst->d_rtbtimer = src->d_rt_spc_timer;
> +	dst->d_rtbtimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_rtbtimer,
> +						  src->d_rt_spc_timer);
>  	dst->d_rtbwarns = src->d_rt_spc_warns;
>  }
>  
> diff --git a/include/uapi/linux/dqblk_xfs.h b/include/uapi/linux/dqblk_xfs.h
> index 03d890b80ebc..a684f64d9cc0 100644
> --- a/include/uapi/linux/dqblk_xfs.h
> +++ b/include/uapi/linux/dqblk_xfs.h
> @@ -71,8 +71,11 @@ typedef struct fs_disk_quota {
>  	__u64		d_rtb_softlimit;/* preferred limit on RT disk blks */
>  	__u64		d_rtbcount;	/* # realtime blocks owned */
>  	__s32		d_rtbtimer;	/* similar to above; for RT disk blks */
> -	__u16	  	d_rtbwarns;     /* # warnings issued wrt RT disk blks */
> -	__s16		d_padding3;	/* padding3 - for future use */	
> +	__u16		d_rtbwarns;     /* # warnings issued wrt RT disk blks */
> +	__s8		d_itimer_hi:5;	/* upper 5 bits of timers */
> +	__s8		d_btimer_hi:5;
> +	__s8		d_rtbtimer_hi:5;
> +	__u8		d_padding3:1;	/* padding3 - for future use */
>  	char		d_padding4[8];	/* yet more padding */
>  } fs_disk_quota_t;

I'm a bit nervous about passing bitfields through kernel-userspace
interface. It *should* work OK but I'm not sure rules for bitfield packing
between different compilers are always compatible. E.g. in this case will
the compiler emit three 1-byte fields (as __s8 kind of suggests), just
masking 5-bits out of each or will it use 16-bit wide memory location with
all four fields packed together? And if this is even defined? I didn't find
anything definitive. Also I've found some notes that the order of bit
fields in a word is implementation defined...

So to save us some headaches, I'd prefer to use just three times __s8 for
the _hi fields and then check whether userspace didn't pass too big values
(more than 5 significant bits) when copying from userspace.

								Honza
Darrick J. Wong Sept. 4, 2020, 3:29 p.m. UTC | #2
On Fri, Sep 04, 2020 at 10:31:23AM +0200, Jan Kara wrote:
> On Thu 03-09-20 22:39:31, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Widen the timestamp fields in struct fs_disk_quota to handle quota grace
> > expiration times beyond 2038.  Since the only filesystem that's going to
> > use this (XFS) only supports unsigned 34-bit quantities, adding an extra
> > 5 bits here should work fine.  We can rev the structure again in 350
> > years.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Some comments below...
> 
> > @@ -588,10 +600,27 @@ static int quota_setxquota(struct super_block *sb, int type, qid_t id,
> >  	return sb->s_qcop->set_dqblk(sb, qid, &qdq);
> >  }
> >  
> > +static inline __s8 copy_to_xfs_dqblk_ts(const struct fs_disk_quota *d,
> > +		__s32 *timer_lo, s64 timer)
> > +{
> > +	*timer_lo = timer;
> > +	if (d->d_fieldmask & FS_DQ_BIGTIME)
> > +		return timer >> 32;
> > +	return 0;
> > +}
> 
> Hum, this function API looks a bit strange to me - directly store timer_lo
> and just return timer_hi... Why not having timer_hi as another function
> argument?

You can't pass pointers to a bitset. :)

> > @@ -606,6 +635,10 @@ static void copy_to_xfs_dqblk(struct fs_disk_quota *dst, struct qc_dqblk *src,
> >  	dst->d_ino_softlimit = src->d_ino_softlimit;
> >  	dst->d_bcount = quota_btobb(src->d_space);
> >  	dst->d_icount = src->d_ino_count;
> > +	dst->d_itimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_itimer,
> > +						src->d_ino_timer);
> > +	dst->d_btimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_btimer,
> > +						src->d_spc_timer);
> >  	dst->d_itimer = src->d_ino_timer;
> >  	dst->d_btimer = src->d_spc_timer;
> 
> Also it seems pointless (if not outright buggy due to sign-extension rules)
> to store to say d_itimer when copy_to_xfs_dqblk_ts() already did it...

Oops.  That was a straight up bug. :(

> >  	dst->d_iwarns = src->d_ino_warns;
> > @@ -613,7 +646,8 @@ static void copy_to_xfs_dqblk(struct fs_disk_quota *dst, struct qc_dqblk *src,
> >  	dst->d_rtb_hardlimit = quota_btobb(src->d_rt_spc_hardlimit);
> >  	dst->d_rtb_softlimit = quota_btobb(src->d_rt_spc_softlimit);
> >  	dst->d_rtbcount = quota_btobb(src->d_rt_space);
> > -	dst->d_rtbtimer = src->d_rt_spc_timer;
> > +	dst->d_rtbtimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_rtbtimer,
> > +						  src->d_rt_spc_timer);
> >  	dst->d_rtbwarns = src->d_rt_spc_warns;
> >  }
> >  
> > diff --git a/include/uapi/linux/dqblk_xfs.h b/include/uapi/linux/dqblk_xfs.h
> > index 03d890b80ebc..a684f64d9cc0 100644
> > --- a/include/uapi/linux/dqblk_xfs.h
> > +++ b/include/uapi/linux/dqblk_xfs.h
> > @@ -71,8 +71,11 @@ typedef struct fs_disk_quota {
> >  	__u64		d_rtb_softlimit;/* preferred limit on RT disk blks */
> >  	__u64		d_rtbcount;	/* # realtime blocks owned */
> >  	__s32		d_rtbtimer;	/* similar to above; for RT disk blks */
> > -	__u16	  	d_rtbwarns;     /* # warnings issued wrt RT disk blks */
> > -	__s16		d_padding3;	/* padding3 - for future use */	
> > +	__u16		d_rtbwarns;     /* # warnings issued wrt RT disk blks */
> > +	__s8		d_itimer_hi:5;	/* upper 5 bits of timers */
> > +	__s8		d_btimer_hi:5;
> > +	__s8		d_rtbtimer_hi:5;
> > +	__u8		d_padding3:1;	/* padding3 - for future use */
> >  	char		d_padding4[8];	/* yet more padding */
> >  } fs_disk_quota_t;
> 
> I'm a bit nervous about passing bitfields through kernel-userspace
> interface. It *should* work OK but I'm not sure rules for bitfield packing
> between different compilers are always compatible. E.g. in this case will
> the compiler emit three 1-byte fields (as __s8 kind of suggests), just
> masking 5-bits out of each or will it use 16-bit wide memory location with
> all four fields packed together? And if this is even defined? I didn't find
> anything definitive. Also I've found some notes that the order of bit
> fields in a word is implementation defined...
> 
> So to save us some headaches, I'd prefer to use just three times __s8 for
> the _hi fields and then check whether userspace didn't pass too big values
> (more than 5 significant bits) when copying from userspace.

Ok.  I was trying to leave the u32 and u64 paddings, but I'll pick
something to burn down.  __s8[3] it is. :)

--D

> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
diff mbox series

Patch

diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index 5444d3c4d93f..efa14d9ee06f 100644
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -481,6 +481,14 @@  static inline u64 quota_btobb(u64 bytes)
 	return (bytes + (1 << XFS_BB_SHIFT) - 1) >> XFS_BB_SHIFT;
 }
 
+static inline s64 copy_from_xfs_dqblk_ts(const struct fs_disk_quota *d,
+		__s32 timer, __s8 timer_hi)
+{
+	if (d->d_fieldmask & FS_DQ_BIGTIME)
+		return (u32)timer | (s64)timer_hi << 32;
+	return timer;
+}
+
 static void copy_from_xfs_dqblk(struct qc_dqblk *dst, struct fs_disk_quota *src)
 {
 	dst->d_spc_hardlimit = quota_bbtob(src->d_blk_hardlimit);
@@ -489,14 +497,18 @@  static void copy_from_xfs_dqblk(struct qc_dqblk *dst, struct fs_disk_quota *src)
 	dst->d_ino_softlimit = src->d_ino_softlimit;
 	dst->d_space = quota_bbtob(src->d_bcount);
 	dst->d_ino_count = src->d_icount;
-	dst->d_ino_timer = src->d_itimer;
-	dst->d_spc_timer = src->d_btimer;
+	dst->d_ino_timer = copy_from_xfs_dqblk_ts(src, src->d_itimer,
+						  src->d_itimer_hi);
+	dst->d_spc_timer = copy_from_xfs_dqblk_ts(src, src->d_btimer,
+						  src->d_btimer_hi);
 	dst->d_ino_warns = src->d_iwarns;
 	dst->d_spc_warns = src->d_bwarns;
 	dst->d_rt_spc_hardlimit = quota_bbtob(src->d_rtb_hardlimit);
 	dst->d_rt_spc_softlimit = quota_bbtob(src->d_rtb_softlimit);
 	dst->d_rt_space = quota_bbtob(src->d_rtbcount);
 	dst->d_rt_spc_timer = src->d_rtbtimer;
+	dst->d_rt_spc_timer = copy_from_xfs_dqblk_ts(src, src->d_rtbtimer,
+						     src->d_rtbtimer_hi);
 	dst->d_rt_spc_warns = src->d_rtbwarns;
 	dst->d_fieldmask = 0;
 	if (src->d_fieldmask & FS_DQ_ISOFT)
@@ -588,10 +600,27 @@  static int quota_setxquota(struct super_block *sb, int type, qid_t id,
 	return sb->s_qcop->set_dqblk(sb, qid, &qdq);
 }
 
+static inline __s8 copy_to_xfs_dqblk_ts(const struct fs_disk_quota *d,
+		__s32 *timer_lo, s64 timer)
+{
+	*timer_lo = timer;
+	if (d->d_fieldmask & FS_DQ_BIGTIME)
+		return timer >> 32;
+	return 0;
+}
+
+static inline bool want_bigtime(s64 timer)
+{
+	return timer > S32_MAX || timer < S32_MIN;
+}
+
 static void copy_to_xfs_dqblk(struct fs_disk_quota *dst, struct qc_dqblk *src,
 			      int type, qid_t id)
 {
 	memset(dst, 0, sizeof(*dst));
+	if (want_bigtime(src->d_ino_timer) || want_bigtime(src->d_spc_timer) ||
+	    want_bigtime(src->d_rt_spc_timer))
+		dst->d_fieldmask |= FS_DQ_BIGTIME;
 	dst->d_version = FS_DQUOT_VERSION;
 	dst->d_id = id;
 	if (type == USRQUOTA)
@@ -606,6 +635,10 @@  static void copy_to_xfs_dqblk(struct fs_disk_quota *dst, struct qc_dqblk *src,
 	dst->d_ino_softlimit = src->d_ino_softlimit;
 	dst->d_bcount = quota_btobb(src->d_space);
 	dst->d_icount = src->d_ino_count;
+	dst->d_itimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_itimer,
+						src->d_ino_timer);
+	dst->d_btimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_btimer,
+						src->d_spc_timer);
 	dst->d_itimer = src->d_ino_timer;
 	dst->d_btimer = src->d_spc_timer;
 	dst->d_iwarns = src->d_ino_warns;
@@ -613,7 +646,8 @@  static void copy_to_xfs_dqblk(struct fs_disk_quota *dst, struct qc_dqblk *src,
 	dst->d_rtb_hardlimit = quota_btobb(src->d_rt_spc_hardlimit);
 	dst->d_rtb_softlimit = quota_btobb(src->d_rt_spc_softlimit);
 	dst->d_rtbcount = quota_btobb(src->d_rt_space);
-	dst->d_rtbtimer = src->d_rt_spc_timer;
+	dst->d_rtbtimer_hi = copy_to_xfs_dqblk_ts(dst, &dst->d_rtbtimer,
+						  src->d_rt_spc_timer);
 	dst->d_rtbwarns = src->d_rt_spc_warns;
 }
 
diff --git a/include/uapi/linux/dqblk_xfs.h b/include/uapi/linux/dqblk_xfs.h
index 03d890b80ebc..a684f64d9cc0 100644
--- a/include/uapi/linux/dqblk_xfs.h
+++ b/include/uapi/linux/dqblk_xfs.h
@@ -71,8 +71,11 @@  typedef struct fs_disk_quota {
 	__u64		d_rtb_softlimit;/* preferred limit on RT disk blks */
 	__u64		d_rtbcount;	/* # realtime blocks owned */
 	__s32		d_rtbtimer;	/* similar to above; for RT disk blks */
-	__u16	  	d_rtbwarns;     /* # warnings issued wrt RT disk blks */
-	__s16		d_padding3;	/* padding3 - for future use */	
+	__u16		d_rtbwarns;     /* # warnings issued wrt RT disk blks */
+	__s8		d_itimer_hi:5;	/* upper 5 bits of timers */
+	__s8		d_btimer_hi:5;
+	__s8		d_rtbtimer_hi:5;
+	__u8		d_padding3:1;	/* padding3 - for future use */
 	char		d_padding4[8];	/* yet more padding */
 } fs_disk_quota_t;
 
@@ -121,6 +124,12 @@  typedef struct fs_disk_quota {
 #define FS_DQ_RTBCOUNT		(1<<14)
 #define FS_DQ_ACCT_MASK		(FS_DQ_BCOUNT | FS_DQ_ICOUNT | FS_DQ_RTBCOUNT)
 
+/*
+ * Quota expiration timestamps are 37-bit signed integers, with the upper 5
+ * bits encoded in the _hi fields.
+ */
+#define FS_DQ_BIGTIME		(1<<15)
+
 /*
  * Various flags related to quotactl(2).
  */