Re: bin/38201: Potential lack of null termination when copying a string

[David Holland <dholland-bugs%netbsd.org@localhost>]

On Tue, Mar 11, 2008 at 06:45:02PM +0000, David Laight wrote:
 >  On Sat, Mar 08, 2008 at 10:25:46PM +0000, David Holland wrote:
 >  > On Sat, Mar 08, 2008 at 07:55:01PM +0000, netbsd%happyjack.org@localhost 
 > wrote:
 >  >  > [who/utmpentry.c]
 >  >  >
 >  >  > In two places, the wrong object is null-terminated after a
 >  >  > strncpy(), resulting in a potential lack of null termination.
 >  > 
 >  > Good catch... but it turns out that those null terminations are
 >  > neither necessary nor useful. I will clean up the mess...
 >  
 >  Actually they were also wrong!
 >  
 >      (void)strncpy(e->host, up->ut_host, sizeof(up->ut_host));
 >  -   e->name[sizeof(e->name) - 1] = '\0';
 >  +   e->host[sizeof(e->host) - 1] = '\0';
 >  
 >  Since e->host is guaranteed to be longer than up->ut_host, and strncpy
 >  is used because up->ut_host might not be null terminated, the correct
 >  line would be:
 >      e->host[sizeof up->ut_host - 1] = 0;
 >
 >  Of course, the code worked because the buffer had just been calloc'ed.

As mrg noted, e->host[sizeof up->ut_host] = 0; would be better.

This is why I changed it around the way I did...

-- 
David A. Holland
dholland%netbsd.org@localhost