linux-kernel - RE: [PATCH] isofs: fix undefined behavior in iso

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Date:   Thu, 13 Jul 2023 14:11:02 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Dan Carpenter' <dan.carpenter@...aro.org>,
        Linke Li <lilinke99@...mail.com>
CC:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, Linke Li <lilinke99@...il.com>
Subject: RE: [PATCH] isofs: fix undefined behavior in iso_date()

From: Dan Carpenter
> Sent: 10 July 2023 10:57
> 
> It looks like maybe there is an issue with "year" as well.
> 
> fs/isofs/util.c
>     19  int iso_date(u8 *p, int flag)
>     20  {
>     21          int year, month, day, hour, minute, second, tz;
>     22          int crtime;
>     23
>     24          year = p[0];
>                        ^^^^^
> year is 0-255.
....
>     32
>     33          if (year < 0) {
>                     ^^^^^^^^
> But this checks year for < 0 which is impossible.  Should it be:
> 
> 	year = (signed char)p[0];?

Or not?

What happens in 2027 ?
I bet the value has to be treated an unsigned.

> 
>     34                  crtime = 0;
>     35          } else {
>     36                  crtime = mktime64(year+1900, month, day, hour, minute, second);
>     37
>     38                  /* sign extend */
>     39                  if (tz & 0x80)
>     40                          tz |= (-1 << 8);

Just change the definition of tz from 'int' to 's8'
and it will all happen 'by magic'.

	David

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