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Subjectprocfs: boot- and runtime configurable access mode for /proc/<pid> dirs
Hi all,

the attached patch enhances the procfs code to allow for modification of
/proc/<pid> dir access modes. It does so
- by hard-wiring (.config) a boot-time default mode (555, 550 or 500)
- which can be overriden by a boot parameter piddir_mode
- and also introduces an inode /proc/piddirs (644) which enables
runtime-configuration (already existing pid-dirs will be updated on next
access)


I started this quite a while back [1] and it worked fine ever since on
my servers. Now I finally enhanced that code by run-time configurability.


Let me know what you think and please CC me on replying.

Thanks,

Daniel


[1] http://lkml.org/lkml/2007/11/20/136
Index: linux-2.6.38/fs/proc/piddirs.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.38/fs/proc/piddirs.c 2011-03-24 04:53:33.596331008 +0100
@@ -0,0 +1,87 @@
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/pid_namespace.h>
+#include <linux/proc_fs.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+#include <linux/seqlock.h>
+#include <linux/time.h>
+#include "internal.h"
+
+/* prototypes */
+static int __init param_piddir_mode(char *buf);
+static int __init proc_piddirs_init(void);
+static int piddirs_proc_open(struct inode *inode, struct file *file);
+static int piddirs_proc_show(struct seq_file *m, void *v);
+static ssize_t piddirs_proc_write(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppos);
+
+/* variables */
+static const struct file_operations piddirs_proc_fops = {
+ .open = piddirs_proc_open,
+ .read = seq_read,
+ .write = piddirs_proc_write,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+/* This char only stores the module parameter.
+ The actual piddir_creation_mode is stored in base.c */
+static char *piddir_mode;
+
+/* module config */
+module_param(piddir_mode, charp, 0);
+MODULE_PARM_DESC(piddir_mode, "Default creation mode");
+module_init(proc_piddirs_init);
+__setup("piddir_mode=", param_piddir_mode);
+
+
+
+
+static int __init param_piddir_mode(char *buf)
+{
+ if (strlen(buf))
+ set_piddir_creation_mode(buf[0]);
+ return 1;
+}
+
+static int __init proc_piddirs_init(void)
+{
+ proc_create(
+ "piddirs",
+ S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH,
+ NULL,
+ &piddirs_proc_fops
+ );
+ return 0;
+}
+
+static int piddirs_proc_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, piddirs_proc_show, NULL);
+}
+
+static int piddirs_proc_show(struct seq_file *m, void *v)
+{
+ seq_printf(m, "%c\n", get_piddir_creation_mode());
+ return 0;
+}
+
+static ssize_t piddirs_proc_write(struct file *file,
+ const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ char tmp;
+
+ if (
+ (count == 2) &&
+ !copy_from_user(&tmp, buf, 1) &&
+ (set_piddir_creation_mode(tmp) == 0)
+ ) {
+ return count;
+ } else {
+ return -EFAULT;
+ }
+}
Index: linux-2.6.38/fs/proc/internal.h
===================================================================
--- linux-2.6.38.orig/fs/proc/internal.h 2011-03-22 10:00:09.717152492 +0100
+++ linux-2.6.38/fs/proc/internal.h 2011-03-22 11:28:42.205497133 +0100
@@ -94,6 +94,10 @@
extern spinlock_t proc_subdir_lock;

struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, struct nameidata *);
+#ifndef CONFIG_PROC_PIDDIRS_UNRESTRICTED
+char get_piddir_creation_mode(void);
+int set_piddir_creation_mode(char mode);
+#endif
int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir);
unsigned long task_vsize(struct mm_struct *);
unsigned long task_statm(struct mm_struct *,
Index: linux-2.6.38/fs/proc/base.c
===================================================================
--- linux-2.6.38.orig/fs/proc/base.c 2011-03-22 10:00:09.797214588 +0100
+++ linux-2.6.38/fs/proc/base.c 2011-03-24 04:54:51.292565614 +0100
@@ -104,6 +104,14 @@
union proc_op op;
};

+#if defined CONFIG_PROC_PIDDIRS_MODE_U
+ char piddir_creation_mode = 'u';
+#elif defined CONFIG_PROC_PIDDIRS_MODE_UG
+ char piddir_creation_mode = 'g';
+#elif defined CONFIG_PROC_PIDDIRS_MODE_UGO
+ char piddir_creation_mode = 'o';
+#endif
+
#define NOD(NAME, MODE, IOP, FOP, OP) { \
.name = (NAME), \
.len = sizeof(NAME) - 1, \
@@ -1779,8 +1787,15 @@
task = get_proc_task(inode);

if (task) {
- if ((inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
- task_dumpable(task)) {
+ if (
+ #ifndef CONFIG_PROC_PIDDIRS_UNRESTRICTED
+ (inode->i_mode == (S_IFDIR|S_IRUSR|S_IXUSR)) ||
+ (inode->i_mode ==
+ (S_IFDIR|S_IRUSR|S_IRGRP|S_IXUSR|S_IXGRP)) ||
+ #endif
+ (inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
+ task_dumpable(task)
+ ) {
rcu_read_lock();
cred = __task_cred(task);
inode->i_uid = cred->euid;
@@ -1791,6 +1806,21 @@
inode->i_gid = 0;
}
inode->i_mode &= ~(S_ISUID | S_ISGID);
+ #ifndef CONFIG_PROC_PIDDIRS_UNRESTRICTED
+ switch (piddir_creation_mode) {
+ case 'u':
+ inode->i_mode &= ~(S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH);
+ break;
+ case 'g':
+ inode->i_mode |= S_IRUSR|S_IXUSR|S_IRGRP|S_IXGRP;
+ inode->i_mode &= ~(S_IROTH|S_IXOTH);
+ break;
+ case 'o':
+ inode->i_mode |= S_IRUGO|S_IXUGO;
+ break;
+ }
+ #endif
+
security_task_to_inode(task, inode);
put_task_struct(task);
return 1;
@@ -2950,6 +2980,35 @@
pid_ns_release_proc(upid->ns);
}

+#ifndef CONFIG_PROC_PIDDIRS_UNRESTRICTED
+char get_piddir_creation_mode(void)
+{
+ return piddir_creation_mode;
+}
+
+int set_piddir_creation_mode(char mode)
+{
+ switch (mode) {
+ case 'u':
+ printk(KERN_INFO "procfs: Setting /proc/<pid>-dir creation"
+ " mode to 500\n");
+ break;
+ case 'g':
+ printk(KERN_INFO "procfs: Setting /proc/<pid>-dir creation"
+ " mode to 550\n");
+ break;
+ case 'o':
+ printk(KERN_INFO "procfs: Setting /proc/<pid>-dir creation"
+ " mode to 555\n");
+ break;
+ default:
+ return -EINVAL;
+ }
+ piddir_creation_mode = mode;
+ return 0;
+}
+#endif
+
static struct dentry *proc_pid_instantiate(struct inode *dir,
struct dentry * dentry,
struct task_struct *task, const void *ptr)
@@ -2961,7 +3020,22 @@
if (!inode)
goto out;

+ #ifndef CONFIG_PROC_PIDDIRS_UNRESTRICTED
+ switch (piddir_creation_mode) {
+ case 'u':
+ inode->i_mode = S_IFDIR|S_IRUSR|S_IXUSR;
+ break;
+ case 'g':
+ inode->i_mode = S_IFDIR|S_IRUSR|S_IRGRP|S_IXUSR|S_IXGRP;
+ break;
+ case 'o':
+ inode->i_mode = S_IFDIR|S_IRUGO|S_IXUGO;
+ break;
+ }
+ #else
inode->i_mode = S_IFDIR|S_IRUGO|S_IXUGO;
+ #endif
+
inode->i_op = &proc_tgid_base_inode_operations;
inode->i_fop = &proc_tgid_base_operations;
inode->i_flags|=S_IMMUTABLE;
Index: linux-2.6.38/fs/proc/Makefile
===================================================================
--- linux-2.6.38.orig/fs/proc/Makefile 2011-03-22 10:00:09.853177027 +0100
+++ linux-2.6.38/fs/proc/Makefile 2011-03-24 03:48:01.520964812 +0100
@@ -27,3 +27,6 @@
proc-$(CONFIG_PROC_DEVICETREE) += proc_devtree.o
proc-$(CONFIG_PRINTK) += kmsg.o
proc-$(CONFIG_PROC_PAGE_MONITOR) += page.o
+proc-$(CONFIG_PROC_PIDDIRS_MODE_UGO) += piddirs.o
+proc-$(CONFIG_PROC_PIDDIRS_MODE_UG) += piddirs.o
+proc-$(CONFIG_PROC_PIDDIRS_MODE_U) += piddirs.o
Index: linux-2.6.38/fs/proc/Kconfig
===================================================================
--- linux-2.6.38.orig/fs/proc/Kconfig 2011-03-22 10:00:09.757199278 +0100
+++ linux-2.6.38/fs/proc/Kconfig 2011-03-24 03:46:28.488680884 +0100
@@ -67,3 +67,73 @@
/proc/pid/smaps, /proc/pid/clear_refs, /proc/pid/pagemap,
/proc/kpagecount, and /proc/kpageflags. Disabling these
interfaces will reduce the size of the kernel by approximately 4kb.
+
+choice PROC_PIDDIRS
+ prompt "Restrict access to /proc/<pid>-dirs"
+ default PROC_PIDDIRS_MODE_UGO
+ help
+ When set to "no restriction", the access mode for /proc/<pid>-dirs is
+ 555 (r-xr-xr-x) which is the traditional behaviour.
+
+
+ Enabling one of the other options has three impacts:
+
+ 1) set the default access mode to the respective value
+
+ 2) enable a boot parameter called piddir_mode; possible values are
+ - 'u': limit to user
+ - 'g': limit to user and group
+ - 'o': no limits (other may read)
+
+ e.g. piddir_mode=u
+
+ 3) enable runtime-configuration of the access modes by issuing e.g.
+ echo g > /proc/piddirs
+ Again, the possible values are 'u', 'g', 'o'.
+
+config PROC_PIDDIRS_UNRESTRICTED
+ bool "no restriction"
+ depends on PROC_FS
+ help
+ Don't restrict access to /proc/<pid>-dirs, i.e. leave mode at 555
+ respectively r-xr-xr-x . Runtime manipulation of access mode is
+ disabled. This is the traditional mode of operation.
+
+ If unsure, say Y.
+
+config PROC_PIDDIRS_MODE_UGO
+ bool "unrestricted by default"
+ depends on PROC_FS
+ help
+ Don't restrict access to /proc/<pid>-dirs, i.e. leave mode at 555
+ (r-xr-xr-x). The default access mode can be changed to 555 during
+ runtime e.g. by issuing
+
+ echo o > /proc/piddirs
+
+ If unsure, say N.
+
+config PROC_PIDDIRS_MODE_UG
+ bool "restrict to user and group by default"
+ depends on PROC_FS
+ help
+ Restrict access to /proc/<pid>-dirs to user and group, i.e. set mode
+ to 550 (r-xr-x---). The default access mode can be changed to 550
+ during runtime e.g. by issuing
+
+ echo g > /proc/piddirs
+
+ If unsure, say N.
+
+config PROC_PIDDIRS_MODE_U
+ bool "restrict to user by default"
+ depends on PROC_FS
+ help
+ Restrict access to /proc/<pid>-dirs to user only, i.e. set mode to
+ 500 (r-x------). The default access mode can be changed to 500 during
+ runtime e.g. by issuing
+
+ echo u > /proc/piddirs
+
+ If unsure, say N.
+endchoice
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