move seccomp from /proc to a prctl

This reduces the memory footprint and it enforces that only the current
task can enable seccomp on itself (this is a requirement for a
strightforward [modulo preempt ;) ] TIF_NOTSC implementation).

Signed-off-by: Andrea Arcangeli <andrea@cpushare.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 51 insertions, 74 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index d0921944e68c..ae3627337a92 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -67,7 +67,6 @@
 #include <linux/mount.h>
 #include <linux/security.h>
 #include <linux/ptrace.h>
-#include <linux/seccomp.h>
 #include <linux/cpuset.h>
 #include <linux/audit.h>
 #include <linux/poll.h>
@@ -817,71 +816,6 @@ static const struct file_operations proc_loginuid_operations = {
 };
 #endif
 
-#ifdef CONFIG_SECCOMP
-static ssize_t seccomp_read(struct file *file, char __user *buf,
-                            size_t count, loff_t *ppos)
-{
-        struct task_struct *tsk = get_proc_task(file->f_dentry->d_inode);
-        char __buf[20];
-        size_t len;
-
-        if (!tsk)
-                return -ESRCH;
-        /* no need to print the trailing zero, so use only len */
-        len = sprintf(__buf, "%u\n", tsk->seccomp.mode);
-        put_task_struct(tsk);
-
-        return simple_read_from_buffer(buf, count, ppos, __buf, len);
-}
-
-static ssize_t seccomp_write(struct file *file, const char __user *buf,
-                             size_t count, loff_t *ppos)
-{
-        struct task_struct *tsk = get_proc_task(file->f_dentry->d_inode);
-        char __buf[20], *end;
-        unsigned int seccomp_mode;
-        ssize_t result;
-
-        result = -ESRCH;
-        if (!tsk)
-                goto out_no_task;
-
-        /* can set it only once to be even more secure */
-        result = -EPERM;
-        if (unlikely(tsk->seccomp.mode))
-                goto out;
-
-        result = -EFAULT;
-        memset(__buf, 0, sizeof(__buf));
-        count = min(count, sizeof(__buf) - 1);
-        if (copy_from_user(__buf, buf, count))
-                goto out;
-
-        seccomp_mode = simple_strtoul(__buf, &end, 0);
-        if (*end == '\n')
-                end++;
-        result = -EINVAL;
-        if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
-                tsk->seccomp.mode = seccomp_mode;
-                set_tsk_thread_flag(tsk, TIF_SECCOMP);
-        } else
-                goto out;
-        result = -EIO;
-        if (unlikely(!(end - __buf)))
-                goto out;
-        result = end - __buf;
-out:
-        put_task_struct(tsk);
-out_no_task:
-        return result;
-}
-
-static const struct file_operations proc_seccomp_operations = {
-        .read           = seccomp_read,
-        .write          = seccomp_write,
-};
-#endif /* CONFIG_SECCOMP */
-
 #ifdef CONFIG_FAULT_INJECTION
 static ssize_t proc_fault_inject_read(struct file * file, char __user * buf,
                                       size_t count, loff_t *ppos)
@@ -2042,9 +1976,6 @@ static const struct pid_entry tgid_base_stuff[] = {
         REG("numa_maps",  S_IRUGO, numa_maps),
 #endif
         REG("mem",        S_IRUSR|S_IWUSR, mem),
-#ifdef CONFIG_SECCOMP
-        REG("seccomp",    S_IRUSR|S_IWUSR, seccomp),
-#endif
         LNK("cwd",        cwd),
         LNK("root",       root),
         LNK("exe",        exe),
@@ -2329,9 +2260,6 @@ static const struct pid_entry tid_base_stuff[] = {
         REG("numa_maps", S_IRUGO, numa_maps),
 #endif
         REG("mem",       S_IRUSR|S_IWUSR, mem),
-#ifdef CONFIG_SECCOMP
-        REG("seccomp",   S_IRUSR|S_IWUSR, seccomp),
-#endif
         LNK("cwd",       cwd),
         LNK("root",      root),
         LNK("exe",       exe),
diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index 52a9be41250d..e2eff9079fe9 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -59,4 +59,8 @@
 # define PR_ENDIAN_LITTLE       1       /* True little endian mode */
 # define PR_ENDIAN_PPC_LITTLE   2       /* "PowerPC" pseudo little endian */
 
+/* Get/set process seccomp mode */
+#define PR_GET_SECCOMP  21
+#define PR_SET_SECCOMP  22
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 3e8b1cf54303..d708974dbfe3 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -4,8 +4,6 @@
 
 #ifdef CONFIG_SECCOMP
 
-#define NR_SECCOMP_MODES 1
-
 #include <linux/thread_info.h>
 #include <asm/seccomp.h>
 
@@ -23,6 +21,9 @@ static inline int has_secure_computing(struct thread_info *ti)
         return unlikely(test_ti_thread_flag(ti, TIF_SECCOMP));
 }
 
+extern long prctl_get_seccomp(void);
+extern long prctl_set_seccomp(unsigned long);
+
 #else /* CONFIG_SECCOMP */
 
 typedef struct { } seccomp_t;
@@ -34,6 +35,16 @@ static inline int has_secure_computing(struct thread_info *ti)
         return 0;
 }
 
+static inline long prctl_get_seccomp(void)
+{
+        return -EINVAL;
+}
+
+static inline long prctl_set_seccomp(unsigned long arg2)
+{
+        return -EINVAL;
+}
+
 #endif /* CONFIG_SECCOMP */
 
 #endif /* _LINUX_SECCOMP_H */
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index c3391b6020e8..1dfa8a509726 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -10,6 +10,7 @@
 #include <linux/sched.h>
 
 /* #define SECCOMP_DEBUG 1 */
+#define NR_SECCOMP_MODES 1
 
 /*
  * Secure computing mode 1 allows only read/write/exit/sigreturn.
@@ -54,3 +55,28 @@ void __secure_computing(int this_syscall)
 #endif
         do_exit(SIGKILL);
 }
+
+long prctl_get_seccomp(void)
+{
+        return current->seccomp.mode;
+}
+
+long prctl_set_seccomp(unsigned long seccomp_mode)
+{
+        long ret;
+
+        /* can set it only once to be even more secure */
+        ret = -EPERM;
+        if (unlikely(current->seccomp.mode))
+                goto out;
+
+        ret = -EINVAL;
+        if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
+                current->seccomp.mode = seccomp_mode;
+                set_thread_flag(TIF_SECCOMP);
+                ret = 0;
+        }
+
+ out:
+        return ret;
+}
diff --git a/kernel/sys.c b/kernel/sys.c
index ed92e2f03342..4d141ae3e802 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -31,6 +31,7 @@
 #include <linux/cn_proc.h>
 #include <linux/getcpu.h>
 #include <linux/task_io_accounting_ops.h>
+#include <linux/seccomp.h>
 
 #include <linux/compat.h>
 #include <linux/syscalls.h>
@@ -2242,6 +2243,13 @@ asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
                         error = SET_ENDIAN(current, arg2);
                         break;
 
+                case PR_GET_SECCOMP:
+                        error = prctl_get_seccomp();
+                        break;
+                case PR_SET_SECCOMP:
+                        error = prctl_set_seccomp(arg2);
+                        break;
+
                 default:
                         error = -EINVAL;
                         break;