RE: Documentation or software - bug?

Randy.Dunlap
2002-04-07T06:41:13Z

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Hi,

Here's my conclusion/opinion.

All of the (networking) BOOLEAN parameters expect newlen (in the
sysctl system call) to be sizeof(int), not 1, but (your) sysctl
program executes the syscall with newlen = 1.

It ([your] sysctl program) should be modified to pass
BOOLEANs as int's.
In other words, BOOLEAN doesn't imply length = 1.

~Randy

---------- Forwarded message ----------

Hi there,

I try to set up a box without procfs, thus I've to set some kernel
parameters using _sysctl().

I wrote a little quick-n-dirty program to set at least integer and
struct ( or better array ) parameters.

I can set all struct, integer and boolean values with this program
except ip_forward.

Due to the docs ip_forward is a BOOLEAN parameter, so the length of the
value array for _sysctl should be 1.

... but ...

in ${KERNELSRC}/net/ipv4/sysctl_net_ipv4.c I find:
snip -->
<-- snap
static int ipv4_sysctl_forward_strategy(ctl_table *table ...
snip -->
<-- snap
if (newlen != sizeof(int))
return -EINVAL;
snip -->

If the config file for my program looks like this:
# CTL_NET IPV4 FORWARD : YES
3 5 8 : 1
I get ``Invalid argument'' from my program.
If the config file for my program looks like this:
3 5 8 : 1 1 1 1
it works and I have a ``1'' in /proc/sys/net/ipv4/ip_forward.
... sure sizeof(int) is 4 on my machine.

My question:
Is there something wrong with the documentation, and NET_IPV4_FORWARD
awaits 4 integers to set/unset IP forwarding, or is something wrong in
sysctl_net_ipv4.c, or did I understand something wrong, and my program
has to be written in some other kind?

My program itself is in the attachment.

Thanks for every help
Frank

PS:
If the configuration file looks like this:
3 5 16 1 : 1
(the ``3 5 8'' is due to sysctl.h only for compatibility with 2.0
kernels, and I run an 2.4.16) i get ENODIR.

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/*****************************************************************************************
** **
** sysconf.c: Version 0.1 15.03.2002 **
** **
** Author: Frank Schaefer <frank.schafer@setuza.cz> **
** **
** Purpose: **
** For security reasons we decided NOT to enable procfs on our firewall. **
** Thus we had to realize an alternative for the settings of kernel parameters. **
** Also for security reasons this program doesn't take any parameters, and all paths **
** etc. will be hardcoded into this program. **
** **
** Files: **
** Configuration file for sysctl: /etc/sysconf.conf **
** **
** Configuration file syntax: **
** - lines starting with a whitespace and lines starting with '#' are comments **
** empty lines are comnments **
** <#> : integer **
** <ws>: whitespace **
** <#>[<ws>[<ws>...[<#><ws>[<ws>...]...]]]:[<ws>...]<#>[<ws>...[<#><ws>[<ws>...]...]] **
** Whereas the part up to the colon is the syscontrol name as described in **
** /usr/include/linux/sysctl.h, and the part after the colon is the values to set **
** **
** !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! **
** !!!!!!!!!! EDIT THE CONFIGURATION FILE WITH EXTREME CAUTION !!!!!!!!!!! **
** !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! **
** There isn't any possibility to check correct settings at this level. Incorrect **
** settings can cause a complete system crash. **
** **
** Return value: **
** 0: all settings due to the configuration file succeeded **
** n: number of attempts to set parameters failed **
** **
*****************************************************************************************/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <linux/unistd.h>
#include <linux/types.h>
#include <linux/sysctl.h>
#include <errno.h>

/* read one line from the configuration file, ignore comments and store the name and
the value in the arrays pointed to by name and value
INPUT: id - filehandle
name - pointer to name array
nlen - where to store length of the name
value - pointer to value array
vlen - where to store length of the value
OUTPUT: 0 : O.K. name and value contain the next parameter to set
1 : end of configuratin file reached name and value doesn't make
sense */
int readconf( FILE* id, int* name, int* nlen, int* value, int* vlen ) {
char *buf, *buffer;
unsigned char indx;
int v_indx = 0, colon = 0;
char c;
int *target = name;

buf = malloc( 80 * sizeof( char ) );
buffer = buf;
do {
if( ! fgets( buffer, 80 * sizeof( char ) , id ) ) {
free( buf );
return( 1 );
}
} while ( ( *buffer == ' ' ) || ( *buffer == '\t' ) || ( *buffer == '#' ) || \
( *buffer == '\n') );
do {
indx = strspn( buffer, "0123456789" );
if( *(buffer + indx) == ':' ) colon = 1;
*(buffer + indx) = '\0';
*(target + v_indx++) = atoi( buffer );
buffer = buffer + indx + 1;
indx = strcspn( buffer, "0123456789" );
c = *(buffer + indx);
*(buffer + indx) = '\0';
if( strcspn( buffer, ":" ) != strlen( buffer ) ) colon = 1;
*(buffer + indx) = c;
buffer = buffer + indx;
if( colon && ( target != value ) ) {
target = value;
*nlen = v_indx;
v_indx = 0;
}
} while ( strlen( buffer ) > 0 );
*vlen = v_indx;
free( buf );
return( 0 );
}

/* Set one parameter in the OS kernel
INPUT: name - pointer to the name array
nlen - length of the array
value - pointer to the value array
vlen - length of the array
OUTPUT: 0 - O.K.
-1 - error */
_syscall1( int, _sysctl, struct __sysctl_args *, args );
int sysctl( int* name, int nlen, void* value, size_t vlen ) {
size_t ovlen = 1;
struct __sysctl_args args = { name, nlen, 0, &ovlen, value, vlen };
return _sysctl( &args );
}

int main( ) {
int name[5], value[16], nlen, vlen, ret = 0;
char cfgfile[] = "/etc/sysconf.conf";
FILE* stream;

stream = fopen( cfgfile, "r" );
if( ! stream ) {
fprintf( stderr, "Could not read configuration file: %s\n", cfgfile );
exit( 1 );
}
while( readconf( stream, name, &nlen, value, &vlen ) != 1 ) {
if( sysctl( name, nlen, (void*)value, (size_t)vlen ) ) {
perror( "sysctl" );
ret++;
}
}
close( stream );
exit( ret );
}