against tytso/dev
--
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@xxxxxxxxxxx>
Reported-by: Mark Harris <mh8928@xxxxxxxxx>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=23732
---
fs/ext4/ext4.h | 49 ++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 42 insertions(+), 7 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index ece5556..f9c6d2f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -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>
@@ -724,19 +725,53 @@ struct move_extent {
<= (EXT4_GOOD_OLD_INODE_SIZE + \
(einode)->i_extra_isize)) \
+/*
+ * We need is 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;
- time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >>
EXT4_EPOCH_BITS;
+ 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.
+ */
+ u64 extra_bits = le32_to_cpu(extra) & EXT4_EPOCH_MASK;
+ if (extra_bits == 3)
+ 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;
}
#define EXT4_INODE_SET_XTIME(xtime, inode, raw_inode) \
--
1.8.1.2
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
