[PATCH v3] date: detect underflow/overflow when parsing dates with timezone offset

From: darcy <acednes@gmail.com>

Overriding the date of a commit to be close to "1970-01-01 00:00:00" with a large enough positive timezone for the equivelant GMT time to be before the epoch is considered valid by `parse_date_basic`. Similar behaviour occurs when using a date close to "2099-12-31 23:59:59" (the maximum date allowed by `tm_to_time_t`) with a large enough negative timezone offset.

This leads to an integer underflow or underflow respectively in the commit timestamp, which is not caught by `git-commit`, but will cause other services to fail, such as `git-fsck`, which, for the first case, reports "badDateOverflow: invalid author/committer line - date causes integer overflow".

Instead check the timezone offset and fail if the resulting time comes before the epoch "1970-01-01T00:00:00Z" or after the maximum date "2099-12-31T23:59:59Z".

Signed-off-by: Darcy Burke <acednes@gmail.com>
---
    fix: prevent date underflow when using positive timezone offset
    
    cc: Patrick Steinhardt ps@pks.im cc: Phillip Wood
    phillip.wood123@gmail.com cc: darcy acednes@gmail.com cc: Jeff King
    peff@peff.net

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1726%2Fdxrcy%2Fmaster-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1726/dxrcy/master-v3
Pull-Request: https://github.com/git/git/pull/1726

Range-diff vs v2:

 1:  db508b2f533 ! 1:  f0de3a2c543 date: detect underflow when parsing dates with positive timezone offset
     @@ Metadata
      Author: darcy <acednes@gmail.com>
      
       ## Commit message ##
     -    date: detect underflow when parsing dates with positive timezone offset
     +    date: detect underflow/overflow when parsing dates with timezone offset
      
          Overriding the date of a commit to be close to "1970-01-01 00:00:00"
     -    with a large enough timezone for the equivelant GMT time to be before
     -    the epoch is considered valid by `parse_date_basic`.
     +    with a large enough positive timezone for the equivelant GMT time to be
     +    before the epoch is considered valid by `parse_date_basic`. Similar
     +    behaviour occurs when using a date close to "2099-12-31 23:59:59" (the
     +    maximum date allowed by `tm_to_time_t`) with a large enough negative
     +    timezone offset.
      
     -    This leads to an integer underflow in the commit timestamp, which is not
     -    caught by `git-commit`, but will cause other services to fail, such as
     -    `git-fsck`, which reports "badDateOverflow: invalid author/committer
     -    line - date causes integer overflow".
     +    This leads to an integer underflow or underflow respectively in the
     +    commit timestamp, which is not caught by `git-commit`, but will cause
     +    other services to fail, such as `git-fsck`, which, for the first case,
     +    reports "badDateOverflow: invalid author/committer line - date causes
     +    integer overflow".
      
          Instead check the timezone offset and fail if the resulting time comes
     -    before the epoch, "1970-01-01T00:00:00Z", when parsing.
     +    before the epoch "1970-01-01T00:00:00Z" or after the maximum date
     +    "2099-12-31T23:59:59Z".
      
          Signed-off-by: Darcy Burke <acednes@gmail.com>
      
       ## date.c ##
     +@@ date.c: static int match_object_header_date(const char *date, timestamp_t *timestamp, in
     + 	return 0;
     + }
     + 
     ++
     ++/* timestamp of 2099-12-31T23:59:59Z, including 32 leap days */
     ++static const time_t timestamp_max = ((2100L - 1970) * 365 + 32) * 24 * 60 * 60 - 1;
     ++
     + /* Gr. strptime is crap for this; it doesn't have a way to require RFC2822
     +    (i.e. English) day/month names, and it doesn't work correctly with %z. */
     + int parse_date_basic(const char *date, timestamp_t *timestamp, int *offset)
      @@ date.c: int parse_date_basic(const char *date, timestamp_t *timestamp, int *offset)
       		}
       	}
     @@ date.c: int parse_date_basic(const char *date, timestamp_t *timestamp, int *offs
      -	if (!tm_gmt)
      +	if (!tm_gmt) {
      +		if (*offset > 0 && *offset * 60 > *timestamp)
     ++			return -1;
     ++		if (*offset < 0 && -*offset * 60 > timestamp_max - *timestamp)
      +			return -1;
       		*timestamp -= *offset * 60;
      +	}
     @@ date.c: int parse_date_basic(const char *date, timestamp_t *timestamp, int *offs
       
      
       ## t/t0006-date.sh ##
     -@@ t/t0006-date.sh: check_parse '2008-02-14 20:30:45 -:30' '2008-02-14 20:30:45 +0000'
     - check_parse '2008-02-14 20:30:45 -05:00' '2008-02-14 20:30:45 -0500'
     +@@ t/t0006-date.sh: check_parse '2008-02-14 20:30:45 -05:00' '2008-02-14 20:30:45 -0500'
       check_parse '2008-02-14 20:30:45' '2008-02-14 20:30:45 -0500' EST5
       check_parse 'Thu, 7 Apr 2005 15:14:13 -0700' '2005-04-07 15:14:13 -0700'
     + 
      +check_parse '1970-01-01 00:00:00' '1970-01-01 00:00:00 +0000'
      +check_parse '1970-01-01 00:00:00 +00' '1970-01-01 00:00:00 +0000'
      +check_parse '1970-01-01 00:00:00 Z' '1970-01-01 00:00:00 +0000'
     @@ t/t0006-date.sh: check_parse '2008-02-14 20:30:45 -:30' '2008-02-14 20:30:45 +00
      +check_parse '1969-12-31 23:59:59 Z' bad
      +check_parse '1969-12-31 23:59:59 +11' bad
      +check_parse '1969-12-31 23:59:59 -11' bad
     - 
     ++
     ++check_parse '2099-12-31 23:59:59' '2099-12-31 23:59:59 +0000'
     ++check_parse '2099-12-31 23:59:59 +00' '2099-12-31 23:59:59 +0000'
     ++check_parse '2099-12-31 23:59:59 Z' '2099-12-31 23:59:59 +0000'
     ++check_parse '2099-12-31 23:59:59 +01' '2099-12-31 23:59:59 +0100'
     ++check_parse '2099-12-31 23:59:59 -01' bad
     ++check_parse '2099-12-31 23:59:59 -11' bad
     ++check_parse '2099-12-31 23:00:00 -01' bad
     ++check_parse '2099-12-31 22:59:59 -01' '2099-12-31 22:59:59 -0100'
     ++check_parse '2100-00-00 00:00:00' bad
     ++check_parse '2099-12-30 00:00:00 -11' '2099-12-30 00:00:00 -1100'
     ++check_parse '2100-00-00 00:00:00 +00' bad
     ++check_parse '2100-00-00 00:00:00 Z' bad
     ++check_parse '2100-00-00 00:00:00 -11' bad
     ++check_parse '2100-00-00 00:00:00 +11' bad
     ++
       check_approxidate() {
       	echo "$1 -> $2 +0000" >expect
     + 	test_expect_${3:-success} "parse approxidate ($1)" "

 date.c          | 12 +++++++++++-
 t/t0006-date.sh | 31 +++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)