Message-Id: <86F06B08-256A-4638-93C4-88C3AE309497@dilger.ca>
Date:	Sat, 7 Dec 2013 15:33:19 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	David Turner <novalis@...alis.org>
Cc:	Mark Harris <mhlk@....us>, Theodore Ts'o <tytso@....edu>,
	Jan Kara <jack@...e.cz>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 1/2] e2fsck: Correct ext4 dates generated by old kernels.

I suspect that any 32-bit systems running at that time will have been updated to have 64-bit time_t or otherwise have windowed the 32-bit time_t to have a new starting epoch.

So I'm willing to punt on decoding the 64-bit value correctly to libc and just assign our time to the system time_t. 

Cheers, Andreas

> On Dec 7, 2013, at 13:02, David Turner <novalis@...alis.org> wrote:
> 
> I went ahead and wrote some tests, and they seem to confirm that
> my patch to e2fsck works as expected (once I added crtime).
> 
> However, as Andreas notes, "we want to verify .. that "debugfs -R
> 'stat testfile'" decodes the times correctly."  Unfortunately, it
> does not, and it is not trivial to fix.  debugfs uses an internal
> function time_to_string(__u32), which calls gmtime or localtime.
> These functions are defined on time_t, which is 32-bits on 32-bit
> Linux systems.  In addition, because time_to_string takes
> an unsigned int, it returns bad results for pre-1970 dates.
> 
> One fix for this would be to include our own gmtime/localtime
> defined on 64-bit integers.  But this is likely to be
> complicated, given the dependence of localtime on timezone data.
> 
> Instead, I decided to simply adjust time_to_string to take a
> time_t.  This means that on 32-bit time_t systems, we will give
> wrong results for post-2038 dates, but correct results for
> pre-1970 dates. (see patch 2/2)
> 
> For the tests, I am looking at the raw value of ctime and
> ctime_extra, which will work regardless of the size of time_t
> 
> Is using time_t acceptable, or do you want me to copy over
> gmtime/localtime from glibc?  Or is there a third approach
> that would be better?
> 
> Also, while I was making this change, I happened to notice that
> there is no dtime_extra field into which to put the extra bits.
> This means that there is still a year 2038 problem with tools
> that deal with deleted files (including the corner case that the
> system is shut down cleanly at the exact second that the bottom
> 32 bits of the current time are zero, leading fsck to believe
> that there was an unclean shutdown).
> 
> I want to make an additional change to correct this.  Since I
> assume it is impossible to add an additional field, I propose to
> use ctime_extra to store the extra bits of dtime on deletion.
> This is a bit hackish, since it does destroy a bit of data, but
> it is significantly better than dtime being totally broken after
> 2038.  What do people think?
> --
> Older kernels on 64-bit machines would incorrectly encode pre-1970
> ext4 dates as post-2311 dates.  Detect and correct this (assuming the
> current date is before 2242).
> 
> Includes tests for this, as well as changes to debugfs to correctly
> set crtimes.
> 
> Signed-off-by: David Turner <novalis@...alis.org>
> ---
> debugfs/set_fields.c                  |  2 +-
> e2fsck/pass1.c                        | 43 ++++++++++++++++
> e2fsck/problem.c                      |  4 ++
> e2fsck/problem.h                      |  4 ++
> lib/extra_epoch.h                     |  2 +
> tests/f_pre_1970_date_encoding/expect | 45 ++++++++++++++++
> tests/f_pre_1970_date_encoding/name   |  1 +
> tests/f_pre_1970_date_encoding/script | 96 +++++++++++++++++++++++++++++++++++
> 8 files changed, 196 insertions(+), 1 deletion(-)
> create mode 100644 lib/extra_epoch.h
> create mode 100644 tests/f_pre_1970_date_encoding/expect
> create mode 100644 tests/f_pre_1970_date_encoding/name
> create mode 100644 tests/f_pre_1970_date_encoding/script
> 
> diff --git a/debugfs/set_fields.c b/debugfs/set_fields.c
> index aad1cd8..f7c55a7 100644
> --- a/debugfs/set_fields.c
> +++ b/debugfs/set_fields.c
> @@ -200,7 +200,7 @@ static struct field_set_info inode_fields[] = {
>        4, parse_uint },
>    { "atime_extra", &set_inode.i_atime_extra, NULL,
>        4, parse_uint },
> -    { "crtime", &set_inode.i_crtime, NULL, 4, parse_uint },
> +    { "crtime", &set_inode.i_crtime, NULL, 4, parse_time },
>    { "crtime_extra", &set_inode.i_crtime_extra, NULL,
>        4, parse_uint },
>    { "bmap", NULL, NULL, 4, parse_bmap, FLAG_ARRAY },
> diff --git a/e2fsck/pass1.c b/e2fsck/pass1.c
> index ab23e42..ecbd79e 100644
> --- a/e2fsck/pass1.c
> +++ b/e2fsck/pass1.c
> @@ -50,6 +50,8 @@
> 
> #include "problem.h"
> 
> +#include "extra_epoch.h"
> +
> #ifdef NO_INLINE_FUNCS
> #define _INLINE_
> #else
> @@ -348,6 +350,21 @@ fix:
>                EXT2_INODE_SIZE(sb), "pass1");
> }
> 
> +static int check_inode_extra_negative_epoch(__u32 xtime, __u32 extra) {
> +    return (xtime & (1 << 31)) != 0 &&
> +        (extra & EXT4_EPOCH_MASK) == EXT4_EPOCH_MASK;
> +}
> +
> +#define CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, xtime) \
> +    check_inode_extra_negative_epoch(inode->i_##xtime, \
> +                     inode->i_##xtime##_extra)
> +
> +/* When today's date is earlier than 2242, we assume that atimes,
> + * ctimes, crtimes, and mtimes with years in the range 2310..2378 are
> + * actually pre-1970 dates mis-encoded.
> + */
> +#define EXT4_EXTRA_NEGATIVE_DATE_CUTOFF 2 * (1LL << 32)
> +
> static void check_inode_extra_space(e2fsck_t ctx, struct problem_context *pctx)
> {
>    struct ext2_super_block *sb = ctx->fs->super;
> @@ -388,6 +405,32 @@ static void check_inode_extra_space(e2fsck_t ctx, struct problem_context *pctx)
>        /* it seems inode has an extended attribute(s) in body */
>        check_ea_in_inode(ctx, pctx);
>    }
> +
> +    /*
> +     * If the inode's extended atime (ctime, crtime, mtime) is stored in
> +     * the old, invalid format, repair it.
> +     */
> +    if (sizeof(time_t) > 4 && ctx->now < EXT4_EXTRA_NEGATIVE_DATE_CUTOFF &&
> +        (CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, atime) ||
> +         CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, ctime) ||
> +         CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, crtime) ||
> +         CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, mtime))) {
> +
> +        if (!fix_problem(ctx, PR_1_EA_TIME_OUT_OF_RANGE, pctx))
> +            return;
> +
> +        if (CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, atime))
> +            inode->i_atime_extra &= ~EXT4_EPOCH_MASK;
> +        if (CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, ctime))
> +            inode->i_ctime_extra &= ~EXT4_EPOCH_MASK;
> +        if (CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, crtime))
> +            inode->i_crtime_extra &= ~EXT4_EPOCH_MASK;
> +        if (CHECK_INODE_EXTRA_NEGATIVE_EPOCH(inode, mtime))
> +            inode->i_mtime_extra &= ~EXT4_EPOCH_MASK;
> +        e2fsck_write_inode_full(ctx, pctx->ino, pctx->inode,
> +                    EXT2_INODE_SIZE(sb), "pass1");
> +    }
> +
> }
> 
> /*
> diff --git a/e2fsck/problem.c b/e2fsck/problem.c
> index 897693a..b212d00 100644
> --- a/e2fsck/problem.c
> +++ b/e2fsck/problem.c
> @@ -1018,6 +1018,10 @@ static struct e2fsck_problem problem_table[] = {
>      N_("@i %i, end of extent exceeds allowed value\n\t(logical @b %c, physical @b %b, len %N)\n"),
>      PROMPT_CLEAR, 0 },
> 
> +  /* Timestamp(s) on inode beyond 2310-04-04 are likely pre-1970 dates. */
> +    { PR_1_EA_TIME_OUT_OF_RANGE,
> +        N_("Timestamp(s) on @i %i beyond 2310-04-04 are likely pre-1970 dates.\n"),
> +        PROMPT_FIX | PR_PREEN_OK | PR_NO_OK, 0 },
> 
>    /* Pass 1b errors */
> 
> diff --git a/e2fsck/problem.h b/e2fsck/problem.h
> index ae1ed26..3710638 100644
> --- a/e2fsck/problem.h
> +++ b/e2fsck/problem.h
> @@ -593,6 +593,10 @@ struct problem_context {
> #define PR_1_EXTENT_INDEX_START_INVALID    0x01006D
> 
> #define PR_1_EXTENT_END_OUT_OF_BOUNDS    0x01006E
> +
> +/* Timestamp(s) on inode beyond 2310-04-04 are likely pre-1970 dates. */
> +#define PR_1_EA_TIME_OUT_OF_RANGE    0x01006F
> +
> /*
>  * Pass 1b errors
>  */
> diff --git a/lib/extra_epoch.h b/lib/extra_epoch.h
> new file mode 100644
> index 0000000..465c43f
> --- /dev/null
> +++ b/lib/extra_epoch.h
> @@ -0,0 +1,2 @@
> +#define EXT4_EPOCH_BITS 2
> +#define EXT4_EPOCH_MASK ((1 << EXT4_EPOCH_BITS) - 1)
> diff --git a/tests/f_pre_1970_date_encoding/expect b/tests/f_pre_1970_date_encoding/expect
> new file mode 100644
> index 0000000..1a71571
> --- /dev/null
> +++ b/tests/f_pre_1970_date_encoding/expect
> @@ -0,0 +1,45 @@
> +times for year-1909 =
> + ctime: 0x8e475440:00000003
> + atime: 0x8e475440:00000003
> + mtime: 0x8e475440:00000003
> +crtime: 0x8e475440:00000003
> +times for year-1979 =
> + ctime: 0x11db6940:00000000
> + atime: 0x11db6940:00000000
> + mtime: 0x11db6940:00000000
> +crtime: 0x11db6940:00000000
> +times for year-2039 =
> + ctime: 0x82a37b40:00000001
> + atime: 0x82a37b40:00000001
> + mtime: 0x82a37b40:00000001
> +crtime: 0x82a37b40:00000001
> +times for year-2139 =
> + ctime: 0x3e9b9940:00000001
> + atime: 0x3e9b9940:00000001
> + mtime: 0x3e9b9940:00000001
> +crtime: 0x3e9b9940:00000001
> +times for year-1909 =
> + ctime: 0x8e475440:00000000
> + atime: 0x8e475440:00000000
> + mtime: 0x8e475440:00000000
> +crtime: 0x8e475440:00000000
> +times for year-1979 =
> + ctime: 0x11db6940:00000000
> + atime: 0x11db6940:00000000
> + mtime: 0x11db6940:00000000
> +crtime: 0x11db6940:00000000
> +times for year-2039 =
> + ctime: 0x82a37b40:00000001
> + atime: 0x82a37b40:00000001
> + mtime: 0x82a37b40:00000001
> +crtime: 0x82a37b40:00000001
> +times for year-2139 =
> + ctime: 0x3e9b9940:00000001
> + atime: 0x3e9b9940:00000001
> + mtime: 0x3e9b9940:00000001
> +crtime: 0x3e9b9940:00000001
> +times for year-1909 =
> + ctime: 0x8e475440:00000003
> + atime: 0x8e475440:00000003
> + mtime: 0x8e475440:00000003
> +crtime: 0x8e475440:00000003
> diff --git a/tests/f_pre_1970_date_encoding/name b/tests/f_pre_1970_date_encoding/name
> new file mode 100644
> index 0000000..9805324
> --- /dev/null
> +++ b/tests/f_pre_1970_date_encoding/name
> @@ -0,0 +1 @@
> +correct mis-encoded pre-1970 dates
> diff --git a/tests/f_pre_1970_date_encoding/script b/tests/f_pre_1970_date_encoding/script
> new file mode 100644
> index 0000000..c3e12f5
> --- /dev/null
> +++ b/tests/f_pre_1970_date_encoding/script
> @@ -0,0 +1,96 @@
> +if test -x $DEBUGFS_EXE; then
> +
> +OUT=$test_name.log
> +TIMESTAMPS=$test_name.timestamps.log
> +EXP=$test_dir/expect
> +FSCK_OPT=-yf
> +
> +create_file_with_xtime_and_extra() {
> +    name=$1
> +    time=$2
> +    extra=$3
> +    $DEBUGFS -w -R "write /dev/null $name" $TMPFILE > $OUT 2>&1
> +    for xtime in atime ctime mtime crtime
> +    do
> +        $DEBUGFS -w -R "set_inode_field $name $xtime @$time" $TMPFILE > $OUT 2>&1
> +
> +        $DEBUGFS -w -R "set_inode_field $name ${xtime}_extra $extra" $TMPFILE > $OUT 2>&1
> +    done
> +}
> +
> +get_file_xtime_and_extra() {
> +    name=$1
> +    echo "times for $name =" >> $TIMESTAMPS
> +    $DEBUGFS -R "stat $name" $TMPFILE 2>&1 | egrep '^( a| c| m|cr)time: ' |sed 's/ --.*//' >> $TIMESTAMPS
> +}
> +
> +rm -f $OUT
> +rm -f $TIMESTAMPS
> +
> +#create an empty ext4 filesystem with 256-byte inodes for testing
> +dd status=none if=/dev/zero of=$TMPFILE bs=1024 count=5000
> +echo  mkfs.ext4 -q -I 256 $TMPFILE >> $OUT
> +yes | mkfs.ext4 -q -I 256 $TMPFILE >> $OUT 2>&1
> +
> +# this is a pre-1970 file encoded with the old encoding.
> +# fsck should repair this
> +create_file_with_xtime_and_extra year-1909 -1907928000 3
> +
> +# these are all already encoded correctly
> +create_file_with_xtime_and_extra year-1979   299592000 0
> +create_file_with_xtime_and_extra year-2039  2191752000 1
> +create_file_with_xtime_and_extra year-2139  5345352000 1
> +
> +# confirm that the xtime is wrong on the pre-1970 file
> +get_file_xtime_and_extra year-1909
> +
> +# and confirm that it is right on the remaining files
> +get_file_xtime_and_extra year-1979
> +get_file_xtime_and_extra year-2039
> +get_file_xtime_and_extra year-2139
> +
> +# before we repair the filesystem, save off a copy so that
> +# we can use it later
> +
> +cp $TMPFILE $TMPFILE.backup
> +
> +# repair the filesystem
> +E2FSCK_TIME=1386393539 $FSCK $FSCK_OPT $TMPFILE >> $OUT 2>&1
> +
> +# check that the dates and xtime_extra on the file is now correct
> +get_file_xtime_and_extra year-1909
> +
> +# check that the remaining dates have not been altered
> +get_file_xtime_and_extra year-1979
> +get_file_xtime_and_extra year-2039
> +get_file_xtime_and_extra year-2139
> +
> +# now we need to check that after the year 2242, e2fsck does not
> +# modify dates with extra_xtime=3
> +
> +# restore the unrepaired filesystem
> +mv $TMPFILE.backup $TMPFILE
> +
> +#retry the repair
> +E2FSCK_TIME=9270393539 $FSCK $FSCK_OPT $TMPFILE >> $OUT 2>&1
> +
> +# check that the 1909 file is unaltered (i.e. it has a post-2378 date)
> +get_file_xtime_and_extra year-1909
> +
> +cmp -s $TIMESTAMPS $EXP
> +status=$?
> +
> +if [ "$status" = 0 ] ; then
> +    echo "$test_name: $test_description: ok"
> +    touch $test_name.ok
> +else
> +    echo "$test_name: $test_description: failed"
> +    diff $DIFF_OPTS $EXP $TIMESTAMPS > $test_name.failed
> +fi
> +
> +unset OUT TIMESTAMPS EXP FSCK_OPT
> +
> +else #if test -x $DEBUGFS_EXE; then
> +    echo "$test_name: $test_description: skipped"
> +fi
> +
> -- 
> 1.8.1.2
> 
> 
> 
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