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

    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)
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