sysctl: deprecate sys_sysctl in a user space visible fashion.

After adding checking to register_sysctl_table and finding a whole new set
of bugs.  Missed by countless code reviews and testers I have finally lost
patience with the binary sysctl interface.

The binary sysctl interface has been sort of deprecated for years and
finding a user space program that uses the syscall is more difficult then
finding a needle in a haystack.  Problems continue to crop up, with the in
kernel implementation.  So since supporting something that no one uses is
silly, deprecate sys_sysctl with a sufficient grace period and notice that
the handful of user space applications that care can be fixed or replaced.

The /proc/sys sysctl interface that people use will continue to be
supported indefinitely.

This patch moves the tested warning about sysctls from the path where
sys_sysctl to a separate path called from both implementations of
sys_sysctl, and it adds a proper entry into
Documentation/feature-removal-schedule.

Allowing us to revisit this in a couple years time and actually kill
sys_sysctl.

[lethal@linux-sh.org: sysctl: Fix syscall disabled build]
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 76 insertions, 23 deletions

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 280ec06573e6..5b25162cd9a4 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -82,6 +82,41 @@ Who:	Dominik Brodowski <linux@brodo.de>
 
 ---------------------------
 
+What:   sys_sysctl
+When:   September 2010
+Option: CONFIG_SYSCTL_SYSCALL
+Why:    The same information is available in a more convenient from
+        /proc/sys, and none of the sysctl variables appear to be
+        important performance wise.
+
+        Binary sysctls are a long standing source of subtle kernel
+        bugs and security issues.
+
+        When I looked several months ago all I could find after
+        searching several distributions were 5 user space programs and
+        glibc (which falls back to /proc/sys) using this syscall.
+
+        The man page for sysctl(2) documents it as unusable for user
+        space programs.
+
+        sysctl(2) is not generally ABI compatible to a 32bit user
+        space application on a 64bit and a 32bit kernel.
+
+        For the last several months the policy has been no new binary
+        sysctls and no one has put forward an argument to use them.
+
+        Binary sysctls issues seem to keep happening appearing so
+        properly deprecating them (with a warning to user space) and a
+        2 year grace warning period will mean eventually we can kill
+        them and end the pain.
+
+        In the mean time individual binary sysctls can be dealt with
+        in a piecewise fashion.
+
+Who:    Eric Biederman <ebiederm@xmission.com>
+
+---------------------------
+
 What:  a.out interpreter support for ELF executables
 When:  2.6.25
 Files: fs/binfmt_elf.c
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 62e53a0de4a3..c25e67e19af7 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -55,6 +55,8 @@
 #include <asm/stacktrace.h>
 #endif
 
+static int deprecated_sysctl_warning(struct __sysctl_args *args);
+
 #if defined(CONFIG_SYSCTL)
 
 /* External variables not in a header file. */
@@ -1347,10 +1349,15 @@ asmlinkage long sys_sysctl(struct __sysctl_args __user *args)
         if (copy_from_user(&tmp, args, sizeof(tmp)))
                 return -EFAULT;
 
+        error = deprecated_sysctl_warning(&tmp);
+        if (error)
+                goto out;
+
         lock_kernel();
         error = do_sysctl(tmp.name, tmp.nlen, tmp.oldval, tmp.oldlenp,
                           tmp.newval, tmp.newlen);
         unlock_kernel();
+out:
         return error;
 }
 #endif /* CONFIG_SYSCTL_SYSCALL */
@@ -2540,35 +2547,19 @@ int sysctl_ms_jiffies(struct ctl_table *table, int __user *name, int nlen,
 
 asmlinkage long sys_sysctl(struct __sysctl_args __user *args)
 {
-        static int msg_count;
         struct __sysctl_args tmp;
-        int name[CTL_MAXNAME];
-        int i;
+        int error;
 
-        /* Read in the sysctl name for better debug message logging */
         if (copy_from_user(&tmp, args, sizeof(tmp)))
                 return -EFAULT;
-        if (tmp.nlen <= 0 || tmp.nlen >= CTL_MAXNAME)
-                return -ENOTDIR;
-        for (i = 0; i < tmp.nlen; i++)
-                if (get_user(name[i], tmp.name + i))
-                        return -EFAULT;
 
-        /* Ignore accesses to kernel.version */
-        if ((tmp.nlen == 2) && (name[0] == CTL_KERN) && (name[1] == KERN_VERSION))
-                goto out;
+        error = deprecated_sysctl_warning(&tmp);
 
-        if (msg_count < 5) {
-                msg_count++;
-                printk(KERN_INFO
-                        "warning: process `%s' used the removed sysctl "
-                        "system call with ", current->comm);
-                for (i = 0; i < tmp.nlen; i++)
-                        printk("%d.", name[i]);
-                printk("\n");
-        }
-out:
-        return -ENOSYS;
+        /* If no error reading the parameters then just -ENOSYS ... */
+        if (!error)
+                error = -ENOSYS;
+
+        return error;
 }
 
 int sysctl_data(struct ctl_table *table, int __user *name, int nlen,
@@ -2608,6 +2599,33 @@ int sysctl_ms_jiffies(struct ctl_table *table, int __user *name, int nlen,
 
 #endif /* CONFIG_SYSCTL_SYSCALL */
 
+static int deprecated_sysctl_warning(struct __sysctl_args *args)
+{
+        static int msg_count;
+        int name[CTL_MAXNAME];
+        int i;
+
+        /* Read in the sysctl name for better debug message logging */
+        for (i = 0; i < args->nlen; i++)
+                if (get_user(name[i], args->name + i))
+                        return -EFAULT;
+
+        /* Ignore accesses to kernel.version */
+        if ((args->nlen == 2) && (name[0] == CTL_KERN) && (name[1] == KERN_VERSION))
+                return 0;
+
+        if (msg_count < 5) {
+                msg_count++;
+                printk(KERN_INFO
+                        "warning: process `%s' used the deprecated sysctl "
+                        "system call with ", current->comm);
+                for (i = 0; i < args->nlen; i++)
+                        printk("%d.", name[i]);
+                printk("\n");
+        }
+        return 0;
+}
+
 /*
  * No sense putting this after each symbol definition, twice,
  * exception granted :-)