[PATCH v3] sysctl: control functionality of /proc/pid/mem

Kees Cook
2012-01-23T21:32:51Z

Add the "proc_pid_mem" sysctl to control whether or not /proc/pid/mem is
allowed to work: 0: disabled, 1: read only, 2: read/write (default).

Signed-off-by: Kees Cook <keescook@chromium.org>
---
v3:
- document the default, thanks to Randy Dunlap.
- remove needless CONFIG_PROC_FS checks, thanks to Eric W. Biederman.
v2:
- fix memory leak in error path, thanks to Ingo Molnar.
---
Documentation/sysctl/kernel.txt | 15 +++++++++++++++
fs/proc/base.c | 14 +++++++++++++-
kernel/sysctl.c | 10 ++++++++++
3 files changed, 38 insertions(+), 1 deletions(-)

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 8c20fbd..9e7bad6 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -56,6 +56,7 @@ show up in /proc/sys/kernel:
- printk_delay
- printk_ratelimit
- printk_ratelimit_burst
+- proc_pid_mem
- randomize_va_space
- real-root-dev ==> Documentation/initrd.txt
- reboot-cmd [ SPARC only ]
@@ -477,6 +478,20 @@ send before ratelimiting kicks in.

==============================================================

+proc_pid_mem:
+
+This option can be used to select the level of access given to potential
+ptracers when using the per-process "mem" file in /proc/pid/mem.
+
+0 - Disable entirely.
+
+1 - Allow potential ptracers read access to process memory, but not writes.
+
+2 - Allow potential ptracers read and write access to process memory. This
+ is the default.
+
+==============================================================
+
randomize_va_space:

This option can be used to select the type of process address
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9cde9ed..53133c7 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -109,6 +109,8 @@ struct pid_entry {
union proc_op op;
};

+int sysctl_proc_pid_mem = 2;
+
#define NOD(NAME, MODE, IOP, FOP, OP) { \
.name = (NAME), \
.len = sizeof(NAME) - 1, \
@@ -699,9 +701,13 @@ static const struct file_operations proc_single_file_operations = {

static int mem_open(struct inode* inode, struct file* file)
{
- struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
+ struct task_struct *task;
struct mm_struct *mm;

+ if (sysctl_proc_pid_mem < 1)
+ return -EACCES;
+
+ task = get_proc_task(file->f_path.dentry->d_inode);
if (!task)
return -ESRCH;

@@ -726,6 +732,9 @@ static ssize_t mem_read(struct file * file, char __user * buf,
unsigned long src = *ppos;
struct mm_struct *mm = file->private_data;

+ if (sysctl_proc_pid_mem < 1)
+ return -EACCES;
+
if (!mm)
return 0;

@@ -770,6 +779,9 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
unsigned long dst = *ppos;
struct mm_struct *mm = file->private_data;

+ if (sysctl_proc_pid_mem < 2)
+ return -EACCES;
+
if (!mm)
return 0;

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index f487f25..6fd4bc0 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -103,6 +103,7 @@ extern int percpu_pagelist_fraction;
extern int compat_log;
extern int latencytop_enabled;
extern int sysctl_nr_open_min, sysctl_nr_open_max;
+extern int sysctl_proc_pid_mem;
#ifndef CONFIG_MMU
extern int sysctl_nr_trim_pages;
#endif
@@ -1004,6 +1005,15 @@ static struct ctl_table kern_table[] = {
.proc_handler = proc_dointvec,
},
#endif
+ {
+ .procname = "proc_pid_mem",
+ .data = &sysctl_proc_pid_mem,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &two,
+ },
{ }
};

--
1.7.0.4