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ext4: Fix handling of extended tv_sec

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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: David Turner <novalis@novalis.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Mark Harris <mh8928@yahoo.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=23732
Cc: stable@vger.kernel.org
This commit is contained in:
David Turner 2015-11-24 14:34:37 -05:00 committed by Theodore Ts'o
parent be69e1c19f
commit a4dad1ae24
1 changed files with 44 additions and 7 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

49
fs/ext4/ext4.h
View file

@ -26,6 +26,7 @@
#include <linux/seqlock.h> #include <linux/seqlock.h>
#include <linux/mutex.h> #include <linux/mutex.h>
#include <linux/timer.h> #include <linux/timer.h>
#include <linux/version.h>
#include <linux/wait.h> #include <linux/wait.h>
#include <linux/blockgroup_lock.h> #include <linux/blockgroup_lock.h>
#include <linux/percpu_counter.h> #include <linux/percpu_counter.h>
@ -727,18 +728,54 @@ struct move_extent {
<= (EXT4_GOOD_OLD_INODE_SIZE + \ <= (EXT4_GOOD_OLD_INODE_SIZE + \
(einode)->i_extra_isize)) \ (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) static inline __le32 ext4_encode_extra_time(struct timespec *time)
{ {
return cpu_to_le32((sizeof(time->tv_sec) > 4 ? u32 extra = sizeof(time->tv_sec) > 4 ?
(time->tv_sec >> 32) & EXT4_EPOCH_MASK : 0) | ((time->tv_sec - (s32)time->tv_sec) >> 32) & EXT4_EPOCH_MASK : 0;
((time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK)); return cpu_to_le32(extra | (time->tv_nsec << EXT4_EPOCH_BITS));
} }
static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra) static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)
{ {
if (sizeof(time->tv_sec) > 4) if (unlikely(sizeof(time->tv_sec) > 4 &&
time->tv_sec |= (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK) (extra & cpu_to_le32(EXT4_EPOCH_MASK)))) {
<< 32; #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; time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
} }