Commit a4dad1ae authored by David Turner's avatar David Turner Committed by Theodore Ts'o
Browse files

ext4: Fix handling of extended tv_sec 



In ext4, the bottom two bits of {a,c,m}time_extra are used to extend
the {a,c,m}time fields, deferring the year 2038 problem to the year
2446.

When decoding these extended fields, for times whose bottom 32 bits
would represent a negative number, sign extension causes the 64-bit
extended timestamp to be negative as well, which is not what's
intended.  This patch corrects that issue, so that the only negative
{a,c,m}times are those between 1901 and 1970 (as per 32-bit signed
timestamps).

Some older kernels might have written pre-1970 dates with 1,1 in the
extra bits.  This patch treats those incorrectly-encoded dates as
pre-1970, instead of post-2311, until kernel 4.20 is released.
Hopefully by then e2fsck will have fixed up the bad data.

Also add a comment explaining the encoding of ext4's extra {a,c,m}time
bits.

Signed-off-by: default avatarDavid Turner <novalis@novalis.org>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reported-by: default avatarMark Harris <mh8928@yahoo.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=23732
Cc: stable@vger.kernel.org
parent be69e1c1

fs/ext4/ext4.h

+44 −7
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ 
#include <linux/seqlock.h>

#include <linux/mutex.h>

#include <linux/timer.h>

#include <linux/version.h>

#include <linux/wait.h>

#include <linux/blockgroup_lock.h>

#include <linux/percpu_counter.h>
@@ -727,18 +728,54 @@ struct move_extent { 
	<= (EXT4_GOOD_OLD_INODE_SIZE +			\

	    (einode)->i_extra_isize))			\



/*

 * We use an encoding that preserves the times for extra epoch "00":

 *

 * extra  msb of                         adjust for signed

 * epoch  32-bit                         32-bit tv_sec to

 * bits   time    decoded 64-bit tv_sec  64-bit tv_sec      valid time range

 * 0 0    1    -0x80000000..-0x00000001  0x000000000 1901-12-13..1969-12-31

 * 0 0    0    0x000000000..0x07fffffff  0x000000000 1970-01-01..2038-01-19

 * 0 1    1    0x080000000..0x0ffffffff  0x100000000 2038-01-19..2106-02-07

 * 0 1    0    0x100000000..0x17fffffff  0x100000000 2106-02-07..2174-02-25

 * 1 0    1    0x180000000..0x1ffffffff  0x200000000 2174-02-25..2242-03-16

 * 1 0    0    0x200000000..0x27fffffff  0x200000000 2242-03-16..2310-04-04

 * 1 1    1    0x280000000..0x2ffffffff  0x300000000 2310-04-04..2378-04-22

 * 1 1    0    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.

 */



static inline __le32 ext4_encode_extra_time(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));

	u32 extra = sizeof(time->tv_sec) > 4 ?

		((time->tv_sec - (s32)time->tv_sec) >> 32) & EXT4_EPOCH_MASK : 0;

	return cpu_to_le32(extra | (time->tv_nsec << EXT4_EPOCH_BITS));

}



static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)

{

       if (sizeof(time->tv_sec) > 4)

	       time->tv_sec |= (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK)

			       << 32;

	if (unlikely(sizeof(time->tv_sec) > 4 &&

			(extra & cpu_to_le32(EXT4_EPOCH_MASK)))) {

#if LINUX_VERSION_CODE < KERNEL_VERSION(4,20,0)

		/* Handle legacy encoding of pre-1970 dates with epoch

		 * bits 1,1.  We assume that by kernel version 4.20,

		 * everyone will have run fsck over the affected

		 * filesystems to correct the problem.  (This

		 * backwards compatibility may be removed before this

		 * time, at the discretion of the ext4 developers.)

		 */

		u64 extra_bits = le32_to_cpu(extra) & EXT4_EPOCH_MASK;

		if (extra_bits == 3 && ((time->tv_sec) & 0x80000000) != 0)

			extra_bits = 0;

		time->tv_sec += extra_bits << 32;

#else

		time->tv_sec += (u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK) << 32;

#endif

	}

	time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;

}

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