Date: Tue, 7 Sep 1999 01:40:02 -0700 (PDT) From: <jkoshy@FreeBSD.org> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/6184: No error if resulting file pos in lseek is negative Message-ID: <199909070840.BAA89146@freefall.freebsd.org>
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The following reply was made to PR kern/6184; it has been noted by GNATS.
From: <jkoshy@FreeBSD.org>
To: FreeBSD-gnats-submit@freebsd.org
Cc: phk@FreeBSD.org, des@FreeBSD.org
Subject: Re: kern/6184: No error if resulting file pos in lseek is negative
Date: Tue, 7 Sep 1999 01:34:55 -0700 (PDT)
This is a multipart MIME message.
--==_Exmh_-3322228240
Content-Type: text/plain
The patch given in the PR seems fine. I've touched it up a little to
avoid some style nits and have reworded the manual page to make the
behaviour clearer. A small test program is included.
Any reason why this shouldn't go into -current? If there aren't any
objections, I'd like to commit this and take the change up with JKH for
merging to 3.3-RC.
Regards,
Koshy
--==_Exmh_-3322228240
Content-Type: text/plain ; name="a.c"
Content-Description: test-program
Content-Disposition: attachment; filename="a.c"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
int main(int argc, char **argv)
{
char *Name = "myfile";
int pos, fd = open(Name,O_WRONLY | O_CREAT,0777);
write(fd,"ABCDEFGH",8);
close(fd);
fd = open(Name,O_RDONLY);
#define fail 1
#define succeed 0
#define TEST_LSEEK(whence, value, shouldfail) do {\
printf("> " #whence "(%d): ", value); \
pos = lseek(fd, value, whence); \
printf((shouldfail ? (pos == -1) : (pos >= 0)) ? "pass\n" : "fail\n"); \
(void) lseek(fd, 0, SEEK_SET); \
} while (0)
TEST_LSEEK(SEEK_CUR, -5, fail);
TEST_LSEEK(SEEK_CUR, +5, succeed);
TEST_LSEEK(SEEK_CUR, +10, succeed);
TEST_LSEEK(SEEK_SET, -5, fail);
TEST_LSEEK(SEEK_SET, +5, succeed);
TEST_LSEEK(SEEK_SET, +10, succeed);
TEST_LSEEK(SEEK_END, -10, fail);
TEST_LSEEK(SEEK_END, -5, succeed);
TEST_LSEEK(SEEK_END, +10, succeed);
return 0;
}
--==_Exmh_-3322228240
Content-Type: text/plain ; name="foo"
Content-Description: revised-lseek-patch
Content-Disposition: attachment; filename="foo"
Index: sys/kern/vfs_syscalls.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/vfs_syscalls.c,v
retrieving revision 1.130
diff -u -r1.130 vfs_syscalls.c
--- vfs_syscalls.c 1999/08/12 20:38:32 1.130
+++ vfs_syscalls.c 1999/09/07 12:28:15
@@ -1423,6 +1423,7 @@
register struct file *fp;
struct vattr vattr;
int error;
+ off_t ofs;
if ((u_int)SCARG(uap, fd) >= fdp->fd_nfiles ||
(fp = fdp->fd_ofiles[SCARG(uap, fd)]) == NULL)
@@ -1431,21 +1432,23 @@
return (ESPIPE);
switch (SCARG(uap, whence)) {
case L_INCR:
- fp->f_offset += SCARG(uap, offset);
+ ofs = fp->f_offset + SCARG(uap, offset);
break;
case L_XTND:
error=VOP_GETATTR((struct vnode *)fp->f_data, &vattr, cred, p);
if (error)
return (error);
- fp->f_offset = SCARG(uap, offset) + vattr.va_size;
+ ofs = SCARG(uap, offset) + vattr.va_size;
break;
case L_SET:
- fp->f_offset = SCARG(uap, offset);
+ ofs = SCARG(uap, offset);
break;
default:
return (EINVAL);
}
- *(off_t *)(p->p_retval) = fp->f_offset;
+ if (ofs < 0)
+ return (EINVAL);
+ *(off_t *)(p->p_retval) = fp->f_offset = ofs;
return (0);
}
Index: lib/libc/sys/lseek.2
===================================================================
RCS file: /home/ncvs/src/lib/libc/sys/lseek.2,v
retrieving revision 1.8
diff -u -r1.8 lseek.2
--- lseek.2 1998/04/19 22:20:08 1.8
+++ lseek.2 1999/09/07 13:03:50
@@ -95,6 +95,7 @@
of the existing end-of-file of the file. If data is later written
at this point, subsequent reads of the data in the gap return
bytes of zeros (until data is actually written into the gap).
+Setting the file offset to negative values is not permitted.
.Pp
Some devices are incapable of seeking. The value of the pointer
associated with such a device is undefined.
@@ -120,7 +121,7 @@
is associated with a pipe, socket, or FIFO.
.It Bq Er EINVAL
.Fa Whence
-is not a proper value.
+is not a proper value or the resulting file offset would be negative.
.El
.Sh SEE ALSO
.Xr dup 2 ,
--==_Exmh_-3322228240--
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