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parsedate: avoid integer overflow

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In C, signed integer overflow is undefined behavior. Thus, the compiler
is allowed to assume that it will not occur. In the check for an
overflow, the developer assumes that the signed integer of type time_t
will wrap around if it overflows. However, this behavior is undefined in
the C standard. Thus, when the compiler sees this, it simplifies t +
delta < t to delta < 0. Since delta > 0 and delta < 0 can't both be
true, the entire if statement is optimized out under certain
optimization levels. Thus, the parsedate function would return
PARSEDATE_OK with an undefined value in the time, instead of return -1 =
PARSEDATE_FAIL.
This commit is contained in:
Eric Lubin 2013-12-10 20:01:07 -08:00 committed by Daniel Stenberg
parent 41d21e460f
commit 7246dffff5
1 changed files with 2 additions and 2 deletions
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4
lib/parsedate.c
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@ -5,7 +5,7 @@
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2012, Daniel Stenberg, <daniel@haxx.se>, et al.
* Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
*
* This software is licensed as described in the file COPYING, which
* you should have received as part of this distribution. The terms
@ -526,7 +526,7 @@ static int parsedate(const char *date, time_t *output)
/* Add the time zone diff between local time zone and GMT. */
long delta = (long)(tzoff!=-1?tzoff:0);
if((delta>0) && (t + delta < t))
if((delta>0) && (t > LONG_MAX - delta))
return -1; /* time_t overflow */
t += delta;