Re: [PATCH 2.6.27-rc5] Allow set RLIMIT_NOFILE to RLIM_INFINITY

[Adam Tkac <vonsch@gmail.com>]

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On Fri, Sep 12, 2008 at 01:20:46PM +0200, Andreas Schwab wrote:
> Adam Tkac <vonsch@gmail.com> writes:
> 
> > diff -puN kernel/sys.c~rlimit-permit-setting-rlimit_nofile-to-rlim_infinity kernel/sys.c
> > --- a/kernel/sys.c~rlimit-permit-setting-rlimit_nofile-to-rlim_infinity
> > +++ a/kernel/sys.c
> > @@ -1532,8 +1532,14 @@ asmlinkage long sys_setrlimit(unsigned i
> >  	if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
> >  	    !capable(CAP_SYS_RESOURCE))
> >  		return -EPERM;
> > -	if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > sysctl_nr_open)
> > -		return -EPERM;
> > +	if (resource == RLIMIT_NOFILE) {
> > +		if (new_rlim.rlim_max == RLIM_INFINITY)
> > +			new_rlim.rlim_max = sysctl_nr_open;
> > +		if (new_rlim.rlim_cur == RLIM_INFINITY)
> > +			new_rlim.rlim_cur = sysctl_nr_open;
> > +		if (new_rlim.rlim_max > sysctl_nr_open)
> > +			return -EPERM;
> 
> This makes it possible to set cur > nr_open (when max = INF but nr_open
> < cur < INF).  You need to check that cur <= max after adjustment.
> 
> Andreas.
> 

Right you are. Improved patch is attached, when cur > max && cur !=
INF after adjustment EINVAL is returned. (cur can be also set to max
but it seems like bad solution for me)

-- 
Adam Tkac


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When a process wants to set the limit of open files to RLIM_INFINITY it
gets EPERM even if it has CAP_SYS_RESOURCE capability.

For example, BIND does:

...
#elif defined(NR_OPEN) && defined(__linux__)
        /*
         * Some Linux kernels don't accept RLIM_INFINIT; the maximum
         * possible value is the NR_OPEN defined in linux/fs.h.
         */
        if (resource == isc_resource_openfiles && rlim_value == RLIM_INFINITY) {
                rl.rlim_cur = rl.rlim_max = NR_OPEN;
                unixresult = setrlimit(unixresource, &rl);
                if (unixresult == 0)
                        return (ISC_R_SUCCESS);
        }
#elif ...

If we allow setting RLIMIT_NOFILE to RLIM_INFINITY we increase portability
- you don't have to check if OS is linux and then use different schema for
limits.

The spec says "Specifying RLIM_INFINITY as any resource limit value on a
successful call to setrlimit() shall inhibit enforcement of that resource
limit." and we're presently not doing that.

Signed-off-by: Adam Tkac <vonsch@gmail.com>
--- a/kernel/sys.c.openfiles
+++ a/kernel/sys.c
@@ -1469,14 +1469,22 @@ asmlinkage long sys_setrlimit(unsigned i
 		return -EINVAL;
 	if (copy_from_user(&new_rlim, rlim, sizeof(*rlim)))
 		return -EFAULT;
-	if (new_rlim.rlim_cur > new_rlim.rlim_max)
-		return -EINVAL;
 	old_rlim = current->signal->rlim + resource;
 	if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
 	    !capable(CAP_SYS_RESOURCE))
 		return -EPERM;
-	if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > sysctl_nr_open)
-		return -EPERM;
+
+	if (resource == RLIMIT_NOFILE) {
+		if (new_rlim.rlim_max == RLIM_INFINITY)
+			new_rlim.rlim_max = sysctl_nr_open;
+		if (new_rlim.rlim_cur == RLIM_INFINITY)
+			new_rlim.rlim_cur = sysctl_nr_open;
+		if (new_rlim.rlim_max > sysctl_nr_open)
+			return -EPERM;
+	}
+
+	if (new_rlim.rlim_cur > new_rlim.rlim_max)
+		return -EINVAL;
 
 	retval = security_task_setrlimit(resource, &new_rlim);
 	if (retval)