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Patch "ext4: Fix handling of extended tv_sec" has been added to the 4.3-stable tree

PATCH [email protected] 1 participant 1 message Feb 14, 2016

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This is a note to let you know that I've just added the patch titled

ext4: Fix handling of extended tv_sec

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-fix-handling-of-extended-tv_sec.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From a4dad1ae24f850410c4e60f22823cba1289b8d52 Mon Sep 17 00:00:00 2001

From: David Turner <[email protected]>
Date: Tue, 24 Nov 2015 14:34:37 -0500
Subject: ext4: Fix handling of extended tv_sec

From: David Turner <[email protected]>

commit a4dad1ae24f850410c4e60f22823cba1289b8d52 upstream.

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 <[email protected]>
Signed-off-by Theodore Ts'o <[email protected]>
Reported-by Mark Harris <[email protected]>

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=23732

Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 fs/ext4/ext4.h |   51 ++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 44 insertions(+), 7 deletions(-)
fs/ext4/ext4.h +44 -7
@@ -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>

@@ -723,19 +724,55 @@ 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;
-       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.  (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;
 }
 
 #define EXT4_INODE_SET_XTIME(xtime, inode, raw_inode)			       \

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/ext4-fix-handling-of-extended-tv_sec.patch