Re: /proc parent &proc_root == NULL?

[John Richard Moser <nigelenki@comcast.net>]

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Al Viro wrote:
> On Wed, Jan 26, 2005 at 09:33:48PM -0500, John Richard Moser wrote:
> 
>>create_proc_entry("kmsg", S_IRUSR, &proc_root);
>>
>>So this is asking for proc_root to be filled?
>>
>>create_proc_entry("kcore", S_IRUSR, NULL);
>>
>>And this is just saying to shove it in proc's root?
> 
> 
> NULL is equivalent to &proc_root in that context; moreover, it's better
> style - drivers really shouldn't be refering to what is procfs-private
> object.
> 
> 
>>I'm trying to locate a specific proc entry, using this lovely piece of
>>code I ripped off:
> 
> 
> That's not something allowed outside of procfs code - lifetime rules
> alone make that a Very Bad Idea(tm).  If that's just debugging - OK,
> but if your code really uses that stuff, I want details on the intended
> use.  In that case your design is almost certainly asking for trouble.
> 

I'm trying to implement parts of grsecurity on top of a framework
similar to LSM (i.e. ripoff) that I wrote as an academic endeavor to
find out how stuff works and get some real-life kernel coding experience.

This particular problem pertains to proc_misc.c and trying to create a
hook for some grsecurity protections that alter the modes on certain
/proc entries.  The chunk of the patch I'm trying to immitate is:


diff -urNp linux-2.6.10/fs/proc/proc_misc.c linux-2.6.10/fs/proc/proc_misc.c
- --- linux-2.6.10/fs/proc/proc_misc.c    2004-12-24 16:34:00 -0500
+++ linux-2.6.10/fs/proc/proc_misc.c    2005-01-08 15:53:52 -0500
@@ -582,6 +582,8 @@ static void create_seq_entry(char *name,
 void __init proc_misc_init(void)
 {
        struct proc_dir_entry *entry;
+       int gr_mode = 0;
+
        static struct {
                char *name;
                int (*read_proc)(char*,char**,off_t,int,int*,void*);
@@ -596,9 +598,13 @@ void __init proc_misc_init(void)
 #ifdef CONFIG_STRAM_PROC
                {"stram",       stram_read_proc},
 #endif
+#ifndef CONFIG_GRKERNSEC_PROC_ADD
                {"devices",     devices_read_proc},
+#endif
                {"filesystems", filesystems_read_proc},
+#ifndef CONFIG_GRKERNSEC_PROC_ADD
                {"cmdline",     cmdline_read_proc},
+#endif
                {"locks",       locks_read_proc},
                {"execdomains", execdomains_read_proc},
                {NULL,}
@@ -606,27 +612,45 @@ void __init proc_misc_init(void)
        for (p = simple_ones; p->name; p++)
                create_proc_read_entry(p->name, 0, NULL, p->read_proc,
NULL);

+#ifdef CONFIG_GRKERNSEC_PROC_USER
+       gr_mode = S_IRUSR;
+#elif CONFIG_GRKERNSEC_PROC_USERGROUP
+       gr_mode = S_IRUSR | S_IRGRP;
+#endif
+#ifdef CONFIG_GRKERNSEC_PROC_ADD
+       create_proc_read_entry("devices", gr_mode, NULL,
&devices_read_proc, NULL);
+       create_proc_read_entry("cmdline", gr_mode, NULL,
&cmdline_read_proc, NULL);
+#endif
+
        proc_symlink("mounts", NULL, "self/mounts");

        /* And now for trickier ones */
        entry = create_proc_entry("kmsg", S_IRUSR, &proc_root);
        if (entry)
                entry->proc_fops = &proc_kmsg_operations;
+#ifdef CONFIG_GRKERNSEC_PROC_ADD
+       create_seq_entry("cpuinfo", gr_mode, &proc_cpuinfo_operations);
+#else
        create_seq_entry("cpuinfo", 0, &proc_cpuinfo_operations);
+#endif
        create_seq_entry("partitions", 0, &proc_partitions_operations);
        create_seq_entry("stat", 0, &proc_stat_operations);
        create_seq_entry("interrupts", 0, &proc_interrupts_operations);
+#ifdef CONFIG_GRKERNSEC_PROC_ADD
+
create_seq_entry("slabinfo",S_IWUSR|gr_mode,&proc_slabinfo_operations);
+#else

create_seq_entry("slabinfo",S_IWUSR|S_IRUGO,&proc_slabinfo_operations);
+#endif
        create_seq_entry("buddyinfo",S_IRUGO,
&fragmentation_file_operations);
        create_seq_entry("vmstat",S_IRUGO, &proc_vmstat_file_operations);
        create_seq_entry("diskstats", 0, &proc_diskstats_operations);
 #ifdef CONFIG_MODULES
- -       create_seq_entry("modules", 0, &proc_modules_operations);
+       create_seq_entry("modules", gr_mode, &proc_modules_operations);
 #endif
 #ifdef CONFIG_SCHEDSTATS
        create_seq_entry("schedstat", 0, &proc_schedstat_operations);
 #endif
- -#ifdef CONFIG_PROC_KCORE
+#if defined(CONFIG_PROC_KCORE) && !defined(CONFIG_GRKERNSEC_PROC_ADD)
        proc_root_kcore = create_proc_entry("kcore", S_IRUSR, NULL);
        if (proc_root_kcore) {
                proc_root_kcore->proc_fops = &proc_kcore_operations;


The above I've been trying to create a security hook for to test out.
I've learned much already, like that breaking proc breaks your system
and causes panics.  :)

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