[01/12] Ext4: Fix extended timestamp encoding and decoding
diff mbox

Message ID 20151120145434.18930.89755.stgit@warthog.procyon.org.uk
State New
Headers show

Commit Message

David Howells Nov. 20, 2015, 2:54 p.m. UTC
The handling of extended timestamps in Ext4 is broken as can be seen in the
output of the test program attached below:

time     extra   bad decode        good decode         bad encode  good encode

--
To unsubscribe from this list: send the line "unsubscribe linux-cifs" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Comments

Andreas Dilger Nov. 24, 2015, 5:37 p.m. UTC | #1
On Nov 20, 2015, at 7:54 AM, David Howells <dhowells@redhat.com> wrote:
> 
> The handling of extended timestamps in Ext4 is broken as can be seen in the
> output of the test program attached below:
> 
> time     extra   bad decode        good decode         bad encode  good encode
> ======== =====   ================= =================   =========== ===========
> ffffffff     0 >  ffffffffffffffff  ffffffffffffffff > *ffffffff 3  ffffffff 0
> 80000000     0 >  ffffffff80000000  ffffffff80000000 > *80000000 3  80000000 0
> 00000000     0 >                 0                 0 >  00000000 0  00000000 0
> 7fffffff     0 >          7fffffff          7fffffff >  7fffffff 0  7fffffff 0
> 80000000     1 > *ffffffff80000000          80000000 > *80000000 0  80000000 1
> ffffffff     1 > *ffffffffffffffff          ffffffff > *ffffffff 0  ffffffff 1
> 00000000     1 >         100000000         100000000 >  00000000 1  00000000 1
> 7fffffff     1 >         17fffffff         17fffffff >  7fffffff 1  7fffffff 1
> 80000000     2 > *ffffffff80000000         180000000 > *80000000 1  80000000 2
> ffffffff     2 > *ffffffffffffffff         1ffffffff > *ffffffff 1  ffffffff 2
> 00000000     2 >         200000000         200000000 >  00000000 2  00000000 2
> 7fffffff     2 >         27fffffff         27fffffff >  7fffffff 2  7fffffff 2
> 80000000     3 > *ffffffff80000000         280000000 > *80000000 2  80000000 3
> ffffffff     3 > *ffffffffffffffff         2ffffffff > *ffffffff 2  ffffffff 3
> 00000000     3 >         300000000         300000000 >  00000000 3  00000000 3
> 7fffffff     3 >         37fffffff         37fffffff >  7fffffff 3  7fffffff 3
> 
> The values marked with asterisks are wrong.
> 
> The problem is that with a 64-bit time, in ext4_decode_extra_time() the
> epoch value is just OR'd with the sign-extended time - which, if negative,
> has all of the upper 32 bits set anyway.  We need to add the epoch instead
> of OR'ing it.  In ext4_encode_extra_time(), the reverse operation needs to
> take place as the 32-bit part of the number of seconds needs to be
> subtracted from the 64-bit value before the epoch is shifted down.
> 
> Since the epoch is presumably unsigned, this has the slightly strange
> effect of, for epochs > 0, putting the 0x80000000-0xffffffff range before
> the 0x00000000-0x7fffffff range.
> 
> This affects all kernels from v2.6.23-rc1 onwards.
> 
> The test program:
> 
> 	#include <stdio.h>
> 
> 	#define EXT4_FITS_IN_INODE(x, y, z) 1
> 	#define EXT4_EPOCH_BITS 2
> 	#define EXT4_EPOCH_MASK ((1 << EXT4_EPOCH_BITS) - 1)
> 	#define EXT4_NSEC_MASK  (~0UL << EXT4_EPOCH_BITS)
> 
> 	#define le32_to_cpu(x) (x)
> 	#define cpu_to_le32(x) (x)
> 	typedef unsigned int __le32;
> 	typedef unsigned int u32;
> 	typedef signed int s32;
> 	typedef unsigned long long __u64;
> 	typedef signed long long s64;
> 
> 	struct timespec {
> 		long long	tv_sec;			/* seconds */
> 		long		tv_nsec;		/* nanoseconds */
> 	};
> 
> 	struct ext4_inode_info {
> 		struct timespec i_crtime;
> 	};
> 
> 	struct ext4_inode {
> 		__le32  i_crtime;       /* File Creation time */
> 		__le32  i_crtime_extra; /* extra FileCreationtime (nsec << 2 | epoch) */
> 	};
> 
> 	/* Incorrect implementation */
> 	static inline void ext4_decode_extra_time_bad(struct timespec *time, __le32 extra)
> 	{
> 	       if (sizeof(time->tv_sec) > 4)
> 		       time->tv_sec |= (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK)
> 				       << 32;
> 	       time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
> 	}
> 
> 	static inline __le32 ext4_encode_extra_time_bad(struct timespec *time)
> 	{
> 	       return cpu_to_le32((sizeof(time->tv_sec) > 4 ?
> 				   (time->tv_sec >> 32) & EXT4_EPOCH_MASK : 0) |
> 				  ((time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK));
> 	}
> 
> 	/* Fixed implementation */
> 	static inline void ext4_decode_extra_time_good(struct timespec *time, __le32 _extra)
> 	{
> 		u32 extra = le32_to_cpu(_extra);
> 		u32 epoch = extra & EXT4_EPOCH_MASK;
> 
> 		time->tv_sec = (s32)time->tv_sec + ((s64)epoch  << 32);
> 		time->tv_nsec = (extra & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
> 	}
> 
> 	static inline __le32 ext4_encode_extra_time_good(struct timespec *time)
> 	{
> 		u32 extra;
> 		s64 epoch = time->tv_sec - (s32)time->tv_sec;
> 
> 		extra = (epoch >> 32) & EXT4_EPOCH_MASK;
> 		extra |= (time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK;
> 		return cpu_to_le32(extra);
> 	}
> 
> 	#define EXT4_INODE_GET_XTIME_BAD(xtime, inode, raw_inode)		\
> 	do {									       \
> 		(inode)->xtime.tv_sec = (signed)le32_to_cpu((raw_inode)->xtime);       \
> 		if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
> 			ext4_decode_extra_time_bad(&(inode)->xtime,		\
> 						   raw_inode->xtime ## _extra);	\
> 		else								       \
> 			(inode)->xtime.tv_nsec = 0;				       \
> 	} while (0)
> 
> 	#define EXT4_INODE_SET_XTIME_BAD(xtime, inode, raw_inode)		\
> 	do {									       \
> 		(raw_inode)->xtime = cpu_to_le32((inode)->xtime.tv_sec);	       \
> 		if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
> 			(raw_inode)->xtime ## _extra =				       \
> 				ext4_encode_extra_time_bad(&(inode)->xtime);	\
> 	} while (0)
> 
> 	#define EXT4_INODE_GET_XTIME_GOOD(xtime, inode, raw_inode)		\
> 	do {									       \
> 		(inode)->xtime.tv_sec = (signed)le32_to_cpu((raw_inode)->xtime);       \
> 		if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
> 			ext4_decode_extra_time_good(&(inode)->xtime,			       \
> 					       raw_inode->xtime ## _extra);	\
> 		else								       \
> 			(inode)->xtime.tv_nsec = 0;				       \
> 	} while (0)
> 
> 	#define EXT4_INODE_SET_XTIME_GOOD(xtime, inode, raw_inode)		\
> 	do {									       \
> 		(raw_inode)->xtime = cpu_to_le32((inode)->xtime.tv_sec);	       \
> 		if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
> 			(raw_inode)->xtime ## _extra =				       \
> 				ext4_encode_extra_time_good(&(inode)->xtime);	\
> 	} while (0)
> 
> 	static const struct test {
> 		unsigned crtime;
> 		unsigned extra;
> 		long long sec;
> 		int nsec;
> 	} tests[] = {
> 		// crtime	extra		tv_sec			tv_nsec
> 		0xffffffff,	0x00000000,	0xffffffffffffffff,	0,
> 		0x80000000,	0x00000000,	0xffffffff80000000,	0,
> 		0x00000000,	0x00000000,	0x0000000000000000,	0,
> 		0x7fffffff,	0x00000000,	0x000000007fffffff,	0,
> 		0x80000000,	0x00000001,	0x0000000080000000,	0,
> 		0xffffffff,	0x00000001,	0x00000000ffffffff,	0,
> 		0x00000000,	0x00000001,	0x0000000100000000,	0,
> 		0x7fffffff,	0x00000001,	0x000000017fffffff,	0,
> 		0x80000000,	0x00000002,	0x0000000180000000,	0,
> 		0xffffffff,	0x00000002,	0x00000001ffffffff,	0,
> 		0x00000000,	0x00000002,	0x0000000200000000,	0,
> 		0x7fffffff,	0x00000002,	0x000000027fffffff,	0,
> 		0x80000000,	0x00000003,	0x0000000280000000,	0,
> 		0xffffffff,	0x00000003,	0x00000002ffffffff,	0,
> 		0x00000000,	0x00000003,	0x0000000300000000,	0,
> 		0x7fffffff,	0x00000003,	0x000000037fffffff,	0,
> 	};
> 
> 	int main()
> 	{
> 		struct ext4_inode_info ii_bad, ii_good;
> 		struct ext4_inode raw, *praw = &raw;
> 		struct ext4_inode raw_bad, *praw_bad = &raw_bad;
> 		struct ext4_inode raw_good, *praw_good = &raw_good;
> 		const struct test *t;
> 		int i, ret = 0;
> 
> 		printf("time     extra   bad decode        good decode         bad encode  good encode\n");
> 		printf("======== =====   ================= =================   =========== ===========\n");
> 		for (i = 0; i < sizeof(tests) / sizeof(t[0]); i++) {
> 			t = &tests[i];
> 			raw.i_crtime = t->crtime;
> 			raw.i_crtime_extra = t->extra;
> 			printf("%08x %5d > ", t->crtime, t->extra);
> 
> 			EXT4_INODE_GET_XTIME_BAD(i_crtime, &ii_bad, praw);
> 			EXT4_INODE_GET_XTIME_GOOD(i_crtime, &ii_good, praw);
> 			if (ii_bad.i_crtime.tv_sec != t->sec ||
> 			    ii_bad.i_crtime.tv_nsec != t->nsec)
> 				printf("*");
> 			else
> 				printf(" ");
> 			printf("%16llx", ii_bad.i_crtime.tv_sec);
> 			printf(" ");
> 			if (ii_good.i_crtime.tv_sec != t->sec ||
> 			    ii_good.i_crtime.tv_nsec != t->nsec) {
> 				printf("*");
> 				ret = 1;
> 			} else {
> 				printf(" ");
> 			}
> 			printf("%16llx", ii_good.i_crtime.tv_sec);
> 
> 			EXT4_INODE_SET_XTIME_BAD(i_crtime, &ii_good, praw_bad);
> 			EXT4_INODE_SET_XTIME_GOOD(i_crtime, &ii_good, praw_good);
> 
> 			printf(" > ");
> 			if (raw_bad.i_crtime != raw.i_crtime ||
> 			    raw_bad.i_crtime_extra != raw.i_crtime_extra)
> 				printf("*");
> 			else
> 				printf(" ");
> 			printf("%08llx %d", raw_bad.i_crtime, raw_bad.i_crtime_extra);
> 			printf(" ");
> 
> 			if (raw_good.i_crtime != raw.i_crtime ||
> 			    raw_good.i_crtime_extra != raw.i_crtime_extra) {
> 				printf("*");
> 				ret = 1;
> 			} else {
> 				printf(" ");
> 			}
> 			printf("%08llx %d", raw_good.i_crtime, raw_good.i_crtime_extra);
> 			printf("\n");
> 		}
> 
> 		return ret;
> 	}
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
> 
> fs/ext4/ext4.h |   22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index fd1f28be5296..31efcd78bf51 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -723,19 +723,23 @@ struct move_extent {
> 	<= (EXT4_GOOD_OLD_INODE_SIZE +			\
> 	    (einode)->i_extra_isize))			\
> 
> -static inline __le32 ext4_encode_extra_time(struct timespec *time)
> +static inline void ext4_decode_extra_time(struct timespec *time, __le32 _extra)
> {
> -       return cpu_to_le32((sizeof(time->tv_sec) > 4 ?
> -			   (time->tv_sec >> 32) & EXT4_EPOCH_MASK : 0) |
> -                          ((time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK));
> +	u32 extra = le32_to_cpu(_extra);
> +	u32 epoch = extra & EXT4_EPOCH_MASK;
> +
> +	time->tv_sec = (s32)time->tv_sec + ((s64)epoch  << 32);

Minor nit - two spaces before "<<".

> +	time->tv_nsec = (extra & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
> }
> 
> -static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)
> +static inline __le32 ext4_encode_extra_time(struct timespec *time)
> {
> -       if (sizeof(time->tv_sec) > 4)
> -	       time->tv_sec |= (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK)
> -			       << 32;
> -       time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
> +	u32 extra;
> +	s64 epoch = time->tv_sec - (s32)time->tv_sec;
> +
> +	extra = (epoch >> 32) & EXT4_EPOCH_MASK;
> +	extra |= (time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK;
> +	return cpu_to_le32(extra);
> }

David, thanks for moving this patch forward.

It would have been easier to review if the order of encode and decode
functions had not been reversed... :-)

It would be good to get a comment block in the code describing the encoding:

/*
 * We need is an encoding that preserves the times for extra epoch "00":
 *
 * extra                          add to 32-bit
 * epoch                          tv_sec to get
 * bits   decoded 64-bit tv_sec   64-bit value    valid time range
 * 0     -0x80000000..-0x00000001  0x000000000    1901-12-13..1969-12-31
 * 0     0x000000000..0x07fffffff  0x000000000    1970-01-01..2038-01-19
 * 1     0x080000000..0x0ffffffff  0x100000000    2038-01-19..2106-02-07
 * 1     0x100000000..0x17fffffff  0x100000000    2106-02-07..2174-02-25
 * 2     0x180000000..0x1ffffffff  0x200000000    2174-02-25..2242-03-16
 * 2     0x200000000..0x27fffffff  0x200000000    2242-03-16..2310-04-04
 * 3     0x280000000..0x2ffffffff  0x300000000    2310-04-04..2378-04-22
 * 3     0x300000000..0x37fffffff  0x300000000    2378-04-22..2446-05-10
 *
 * Note that previous versions of the kernel on 64-bit systems would
 * incorrectly use extra epoch bits 1,1 for dates between 1901 and 1970.
 * e2fsck will correct this, assuming that it is run on the affected
 * filesystem before 2242.
 */


The only other question is whether you compile tested this on a 32-bit
system?  IIRC, the "sizeof(time->tv_sec)" check was to avoid compiler
warnings due to assigning values too large for the data type, and (to
a lesser extent) avoiding overhead on those systems.

If there is no 32-bit compile warning then I'm fine with this as-is,
since systems with 32-bit tv_sec are going to be broken at that point
in any case.

Cheers, Andreas

Patch
diff mbox

======== =====   ================= =================   =========== ===========
ffffffff     0 >  ffffffffffffffff  ffffffffffffffff > *ffffffff 3  ffffffff 0
80000000     0 >  ffffffff80000000  ffffffff80000000 > *80000000 3  80000000 0
00000000     0 >                 0                 0 >  00000000 0  00000000 0
7fffffff     0 >          7fffffff          7fffffff >  7fffffff 0  7fffffff 0
80000000     1 > *ffffffff80000000          80000000 > *80000000 0  80000000 1
ffffffff     1 > *ffffffffffffffff          ffffffff > *ffffffff 0  ffffffff 1
00000000     1 >         100000000         100000000 >  00000000 1  00000000 1
7fffffff     1 >         17fffffff         17fffffff >  7fffffff 1  7fffffff 1
80000000     2 > *ffffffff80000000         180000000 > *80000000 1  80000000 2
ffffffff     2 > *ffffffffffffffff         1ffffffff > *ffffffff 1  ffffffff 2
00000000     2 >         200000000         200000000 >  00000000 2  00000000 2
7fffffff     2 >         27fffffff         27fffffff >  7fffffff 2  7fffffff 2
80000000     3 > *ffffffff80000000         280000000 > *80000000 2  80000000 3
ffffffff     3 > *ffffffffffffffff         2ffffffff > *ffffffff 2  ffffffff 3
00000000     3 >         300000000         300000000 >  00000000 3  00000000 3
7fffffff     3 >         37fffffff         37fffffff >  7fffffff 3  7fffffff 3

The values marked with asterisks are wrong.

The problem is that with a 64-bit time, in ext4_decode_extra_time() the
epoch value is just OR'd with the sign-extended time - which, if negative,
has all of the upper 32 bits set anyway.  We need to add the epoch instead
of OR'ing it.  In ext4_encode_extra_time(), the reverse operation needs to
take place as the 32-bit part of the number of seconds needs to be
subtracted from the 64-bit value before the epoch is shifted down.

Since the epoch is presumably unsigned, this has the slightly strange
effect of, for epochs > 0, putting the 0x80000000-0xffffffff range before
the 0x00000000-0x7fffffff range.

This affects all kernels from v2.6.23-rc1 onwards.

The test program:

	#include <stdio.h>

	#define EXT4_FITS_IN_INODE(x, y, z) 1
	#define EXT4_EPOCH_BITS 2
	#define EXT4_EPOCH_MASK ((1 << EXT4_EPOCH_BITS) - 1)
	#define EXT4_NSEC_MASK  (~0UL << EXT4_EPOCH_BITS)

	#define le32_to_cpu(x) (x)
	#define cpu_to_le32(x) (x)
	typedef unsigned int __le32;
	typedef unsigned int u32;
	typedef signed int s32;
	typedef unsigned long long __u64;
	typedef signed long long s64;

	struct timespec {
		long long	tv_sec;			/* seconds */
		long		tv_nsec;		/* nanoseconds */
	};

	struct ext4_inode_info {
		struct timespec i_crtime;
	};

	struct ext4_inode {
		__le32  i_crtime;       /* File Creation time */
		__le32  i_crtime_extra; /* extra FileCreationtime (nsec << 2 | epoch) */
	};

	/* Incorrect implementation */
	static inline void ext4_decode_extra_time_bad(struct timespec *time, __le32 extra)
	{
	       if (sizeof(time->tv_sec) > 4)
		       time->tv_sec |= (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK)
				       << 32;
	       time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
	}

	static inline __le32 ext4_encode_extra_time_bad(struct timespec *time)
	{
	       return cpu_to_le32((sizeof(time->tv_sec) > 4 ?
				   (time->tv_sec >> 32) & EXT4_EPOCH_MASK : 0) |
				  ((time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK));
	}

	/* Fixed implementation */
	static inline void ext4_decode_extra_time_good(struct timespec *time, __le32 _extra)
	{
		u32 extra = le32_to_cpu(_extra);
		u32 epoch = extra & EXT4_EPOCH_MASK;

		time->tv_sec = (s32)time->tv_sec + ((s64)epoch  << 32);
		time->tv_nsec = (extra & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
	}

	static inline __le32 ext4_encode_extra_time_good(struct timespec *time)
	{
		u32 extra;
		s64 epoch = time->tv_sec - (s32)time->tv_sec;

		extra = (epoch >> 32) & EXT4_EPOCH_MASK;
		extra |= (time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK;
		return cpu_to_le32(extra);
	}

	#define EXT4_INODE_GET_XTIME_BAD(xtime, inode, raw_inode)		\
	do {									       \
		(inode)->xtime.tv_sec = (signed)le32_to_cpu((raw_inode)->xtime);       \
		if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
			ext4_decode_extra_time_bad(&(inode)->xtime,		\
						   raw_inode->xtime ## _extra);	\
		else								       \
			(inode)->xtime.tv_nsec = 0;				       \
	} while (0)

	#define EXT4_INODE_SET_XTIME_BAD(xtime, inode, raw_inode)		\
	do {									       \
		(raw_inode)->xtime = cpu_to_le32((inode)->xtime.tv_sec);	       \
		if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
			(raw_inode)->xtime ## _extra =				       \
				ext4_encode_extra_time_bad(&(inode)->xtime);	\
	} while (0)

	#define EXT4_INODE_GET_XTIME_GOOD(xtime, inode, raw_inode)		\
	do {									       \
		(inode)->xtime.tv_sec = (signed)le32_to_cpu((raw_inode)->xtime);       \
		if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
			ext4_decode_extra_time_good(&(inode)->xtime,			       \
					       raw_inode->xtime ## _extra);	\
		else								       \
			(inode)->xtime.tv_nsec = 0;				       \
	} while (0)

	#define EXT4_INODE_SET_XTIME_GOOD(xtime, inode, raw_inode)		\
	do {									       \
		(raw_inode)->xtime = cpu_to_le32((inode)->xtime.tv_sec);	       \
		if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
			(raw_inode)->xtime ## _extra =				       \
				ext4_encode_extra_time_good(&(inode)->xtime);	\
	} while (0)

	static const struct test {
		unsigned crtime;
		unsigned extra;
		long long sec;
		int nsec;
	} tests[] = {
		// crtime	extra		tv_sec			tv_nsec
		0xffffffff,	0x00000000,	0xffffffffffffffff,	0,
		0x80000000,	0x00000000,	0xffffffff80000000,	0,
		0x00000000,	0x00000000,	0x0000000000000000,	0,
		0x7fffffff,	0x00000000,	0x000000007fffffff,	0,
		0x80000000,	0x00000001,	0x0000000080000000,	0,
		0xffffffff,	0x00000001,	0x00000000ffffffff,	0,
		0x00000000,	0x00000001,	0x0000000100000000,	0,
		0x7fffffff,	0x00000001,	0x000000017fffffff,	0,
		0x80000000,	0x00000002,	0x0000000180000000,	0,
		0xffffffff,	0x00000002,	0x00000001ffffffff,	0,
		0x00000000,	0x00000002,	0x0000000200000000,	0,
		0x7fffffff,	0x00000002,	0x000000027fffffff,	0,
		0x80000000,	0x00000003,	0x0000000280000000,	0,
		0xffffffff,	0x00000003,	0x00000002ffffffff,	0,
		0x00000000,	0x00000003,	0x0000000300000000,	0,
		0x7fffffff,	0x00000003,	0x000000037fffffff,	0,
	};

	int main()
	{
		struct ext4_inode_info ii_bad, ii_good;
		struct ext4_inode raw, *praw = &raw;
		struct ext4_inode raw_bad, *praw_bad = &raw_bad;
		struct ext4_inode raw_good, *praw_good = &raw_good;
		const struct test *t;
		int i, ret = 0;

		printf("time     extra   bad decode        good decode         bad encode  good encode\n");
		printf("======== =====   ================= =================   =========== ===========\n");
		for (i = 0; i < sizeof(tests) / sizeof(t[0]); i++) {
			t = &tests[i];
			raw.i_crtime = t->crtime;
			raw.i_crtime_extra = t->extra;
			printf("%08x %5d > ", t->crtime, t->extra);

			EXT4_INODE_GET_XTIME_BAD(i_crtime, &ii_bad, praw);
			EXT4_INODE_GET_XTIME_GOOD(i_crtime, &ii_good, praw);
			if (ii_bad.i_crtime.tv_sec != t->sec ||
			    ii_bad.i_crtime.tv_nsec != t->nsec)
				printf("*");
			else
				printf(" ");
			printf("%16llx", ii_bad.i_crtime.tv_sec);
			printf(" ");
			if (ii_good.i_crtime.tv_sec != t->sec ||
			    ii_good.i_crtime.tv_nsec != t->nsec) {
				printf("*");
				ret = 1;
			} else {
				printf(" ");
			}
			printf("%16llx", ii_good.i_crtime.tv_sec);

			EXT4_INODE_SET_XTIME_BAD(i_crtime, &ii_good, praw_bad);
			EXT4_INODE_SET_XTIME_GOOD(i_crtime, &ii_good, praw_good);

			printf(" > ");
			if (raw_bad.i_crtime != raw.i_crtime ||
			    raw_bad.i_crtime_extra != raw.i_crtime_extra)
				printf("*");
			else
				printf(" ");
			printf("%08llx %d", raw_bad.i_crtime, raw_bad.i_crtime_extra);
			printf(" ");

			if (raw_good.i_crtime != raw.i_crtime ||
			    raw_good.i_crtime_extra != raw.i_crtime_extra) {
				printf("*");
				ret = 1;
			} else {
				printf(" ");
			}
			printf("%08llx %d", raw_good.i_crtime, raw_good.i_crtime_extra);
			printf("\n");
		}

		return ret;
	}

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/ext4/ext4.h |   22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index fd1f28be5296..31efcd78bf51 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -723,19 +723,23 @@  struct move_extent {
 	<= (EXT4_GOOD_OLD_INODE_SIZE +			\
 	    (einode)->i_extra_isize))			\
 
-static inline __le32 ext4_encode_extra_time(struct timespec *time)
+static inline void ext4_decode_extra_time(struct timespec *time, __le32 _extra)
 {
-       return cpu_to_le32((sizeof(time->tv_sec) > 4 ?
-			   (time->tv_sec >> 32) & EXT4_EPOCH_MASK : 0) |
-                          ((time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK));
+	u32 extra = le32_to_cpu(_extra);
+	u32 epoch = extra & EXT4_EPOCH_MASK;
+
+	time->tv_sec = (s32)time->tv_sec + ((s64)epoch  << 32);
+	time->tv_nsec = (extra & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
 }
 
-static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)
+static inline __le32 ext4_encode_extra_time(struct timespec *time)
 {
-       if (sizeof(time->tv_sec) > 4)
-	       time->tv_sec |= (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK)
-			       << 32;
-       time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
+	u32 extra;
+	s64 epoch = time->tv_sec - (s32)time->tv_sec;
+
+	extra = (epoch >> 32) & EXT4_EPOCH_MASK;
+	extra |= (time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK;
+	return cpu_to_le32(extra);
 }
 
 #define EXT4_INODE_SET_XTIME(xtime, inode, raw_inode)			       \