Thanks for your patient and detailed comments.
--
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.
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 | 61 +++++++++++++++++++++++++++++++++++++---------------------
1 file changed, 39 insertions(+), 22 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 18aa56b..ac54dac 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>
@@ -713,38 +714,54 @@ struct move_extent {
sizeof((ext4_inode)->field)) \
<= (EXT4_GOOD_OLD_INODE_SIZE + \
(einode)->i_extra_isize)) \
+
/*
- * We use the bottom 34 bits of the signed 64-bit time value, with
- * the top two of these bits in the bottom of extra. This leads
- * to a slightly odd encoding, which works like this:
+ * We need is an encoding that preserves the times for extra epoch "00":
*
- * extra msb of
- * epoch 32-bit
- * bits time decoded 64-bit tv_sec valid time range
- * 0 0 0 0x000000000..0x07fffffff 1970-01-01..2038-01-19
- * 0 0 1 0x080000000..0x0ffffffff 2038-01-19..2106-02-07
- * 0 1 0 0x100000000..0x17fffffff 2106-02-07..2174-02-25
- * 0 1 1 0x180000000..0x1ffffffff 2174-02-25..2242-03-16
- * 1 0 0 0x200000000..0x27fffffff 2242-03-16..2310-04-04
- * 1 0 1 0x280000000..0x2ffffffff 2310-04-04..2378-04-22
- * 1 1 0 0x300000000..0x37fffffff 2378-04-22..2446-05-10
-
- * 1 1 1 -0x80000000..-0x00000001 1901-12-13..1969-12-31
+ * 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
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