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Date: Tue, 31 Mar 1998 17:40:17 +0200 (CEST)
From: Kent Boortz <kent@erix.ericsson.se>
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Subject: kern/6184: No error if resulting file pos in lseek is negative
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>Number:         6184
>Category:       kern
>Synopsis:       No error if resulting file pos in lseek is negative
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:
>Keywords:
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Mar 31 07:50:02 PST 1998
>Last-Modified:
>Originator:
>Organization:
Ericsson Software Technology
>Release:        FreeBSD 2.2.5-STABLE i386
>Environment:
 
>Description:
 
In FreeBSD 2.2.5 lseek moves the file position without any error
checks. If the resulting position is negative we have the problem that
the result value -1 can mean two things, that there was an error or
that the file position was set to -1 and no error. We have to clear
errno before the call and examine errno after the call to find out if
there was an error or not.
 
If the resulting position is negative, Linux and Solaris will
preserve the file position before the call to lseek and return an
error.
 
Is this a bug in FreeBSD or a different interpretations of the POSIX
standard?
 
>How-To-Repeat:
 
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
 
void main()
{
  char *Name = "myfile";
  int pos, fd = open(Name,O_WRONLY | O_CREAT);
 
  write(fd,"ABCDEFGH",8);
  close(fd);
 
  fd = open(Name,O_RDONLY);
 
  if ((pos = lseek(fd,-5,SEEK_CUR)) != -1) {
    printf("No error moving to pos -5: %d\n",pos);
    exit(1);
  }

  printf("ERROR: %s\n",strerror(errno));
 
  pos = lseek(fd,0,SEEK_CUR);
 
  printf("The error moved the file pointer to: %d\n",pos);
}

>Fix:
	
I belive the fix should be in the file
"/usr/src/sys/kern/vfs_syscalls.c" and the function lseek(). Prior to
setting the new file position the function should test if the new
value is negative. If so the old position should be preserved and the
function return an error with errno EINVAL.
>Audit-Trail:
>Unformatted:

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