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    Subject[PATCH 3.16.y-ckt 007/128] ext4: Fix handling of extended tv_sec
    Date
    3.16.7-ckt23 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: David Turner <novalis@novalis.org>

    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 <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
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    fs/ext4/ext4.h | 51 ++++++++++++++++++++++++++++++++++++++++++++-------
    1 file changed, 44 insertions(+), 7 deletions(-)

    diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
    index e00dc9772402..0798c0bfe57b 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>
    @@ -727,19 +728,55 @@ 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) \
    \
     
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