Re: [PATCH v5] Added PR_SET_PROCTITLE_AREA option for prctl()

["Américo Wang" <xiyou.wangcong@gmail.com>]

On Wed, Nov 04, 2009 at 12:26:44AM +0900, KOSAKI Motohiro wrote:
>> > >+		case PR_SET_PROCTITLE_AREA: {
>> > >+			struct mm_struct *mm = current->mm;
>> > >+			unsigned long addr = arg2;
>> > >+			unsigned long len = arg3;
>> > >+			unsigned long end = arg2 + arg3;
>> > >+
>> > >+			if (len > PAGE_SIZE)
>> > >+				return -EINVAL;
>> > >+
>> > >+			if (addr >= end)
>> > >+				return -EINVAL;
>> > >+
>> > >+			if (!access_ok(VERIFY_READ, addr, len))
>> > >+				return -EFAULT;
>> > >+
>> > >+			mutex_lock(&mm->arg_lock);
>> > >+			mm->arg_start = addr;
>> > 
>> > Is this safe? You're assigning a user-space pointer to kernel space...
>> > Don't we need copy_from_user()?
>> 
>> mm->arg_start, arg_end are defined so.
>> Please see current implementation. 

Hmm, yeah.

>> 
>> 
>> > >+			mm->arg_end = addr + len;
>> > 
>> > Since you already have 'end', no need to caculate this again. :)
>> 
>> Good catch :)
>> 
>> 
>
>Fixed.
>
>
>ChangeLog
>  v4 -> v5
>    - nit: kill duplicate calculation in prctl()
>  v3 -> v4
>    - Use mutex instead seq_lock.
>
>========================================
>
>Subject: [PATCH v5] Added PR_SET_PROCTITLE_AREA option for prctl()
>From: Timo Sirainen <tss@iki.fi>
>
>Currently glibc2 doesn't have setproctitle(3), so several userland
>daemons attempt to emulate it by doing some brutal stack modifications.
>This works most of the time, but it has problems. For example:
>
> % ps -ef |grep avahi-daemon
> avahi     1679     1  0 09:20 ?        00:00:00 avahi-daemon: running [kosadesk.local]
>
> # cat /proc/1679/cmdline
> avahi-daemon: running [kosadesk.local]
>
>This looks good, but the process has also overwritten its environment
>area and made the environ file useless:
>
> # cat /proc/1679/environ
> adesk.local]
>
>Another problem is that the process title length is limited by the size of
>the environment. Security conscious people try to avoid potential information
>leaks by clearing most of the environment before running a daemon:
>
> # env - MINIMUM_NEEDED_VAR=foo /path/to/daemon
>
>The resulting environment size may be too small to fit the wanted process
>titles.
>
>This patch makes it possible for userspace to implement setproctitle()
>cleanly. It adds a new PR_SET_PROCTITLE_AREA option for prctl(), which
>updates task's mm_struct->arg_start and arg_end to the given area.
>
> test_setproctitle.c
> ================================================
> #include <string.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <sys/prctl.h>
>
> #define ERR(str) (perror(str), exit(1))
>
> void settitle(char* title){
>         int err;
>
>         err = prctl(34, title, strlen(title)+1);
>         if (err < 0)
>                 ERR("prctl ");
> }
>
> void main(void){
>         long i;
>         char buf[1024];
>
>         for (i = 0; i < 10000000000LL; i++){
>                 sprintf(buf, "loooooooooooooooooooooooong string %d",i);
>                 settitle(buf);
>         }
> }
> ==================================================
>
>Cc: Bryan Donlan <bdonlan@gmail.com>
>Cc: Ulrich Drepper <drepper@redhat.com>
>Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>Signed-off-by: Timo Sirainen <tss@iki.fi>


This version looks good,

Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>

Thanks!

>---
> fs/proc/base.c           |   31 ++++++++++++++++++++++---------
> include/linux/mm_types.h |    2 ++
> include/linux/prctl.h    |    3 +++
> kernel/fork.c            |    1 +
> kernel/sys.c             |   22 ++++++++++++++++++++++
> 5 files changed, 50 insertions(+), 9 deletions(-)
>
>diff --git a/fs/proc/base.c b/fs/proc/base.c
>index 837469a..ac800b4 100644
>--- a/fs/proc/base.c
>+++ b/fs/proc/base.c
>@@ -255,32 +255,45 @@ static int proc_pid_cmdline(struct task_struct *task, char * buffer)
> 	int res = 0;
> 	unsigned int len;
> 	struct mm_struct *mm = get_task_mm(task);
>+
> 	if (!mm)
> 		goto out;
>+
>+	/* The process was not constructed yet? */
> 	if (!mm->arg_end)
> 		goto out_mm;	/* Shh! No looking before we're done */
> 
>- 	len = mm->arg_end - mm->arg_start;
>- 
>+	mutex_lock(&mm->arg_lock);
>+	len = mm->arg_end - mm->arg_start;
> 	if (len > PAGE_SIZE)
> 		len = PAGE_SIZE;
>- 
>+
> 	res = access_process_vm(task, mm->arg_start, buffer, len, 0);
>+	if (mm->arg_end != mm->env_start)
>+		/* prctl(PR_SET_PROCTITLE_AREA) used */
>+		goto out_unlock;
> 
>-	// If the nul at the end of args has been overwritten, then
>-	// assume application is using setproctitle(3).
>+	/*
>+	 * If the nul at the end of args has been overwritten, then assume
>+	 * application is using sendmail's SPT_REUSEARGV style argv override.
>+	 */
> 	if (res > 0 && buffer[res-1] != '\0' && len < PAGE_SIZE) {
> 		len = strnlen(buffer, res);
>-		if (len < res) {
>-		    res = len;
>-		} else {
>+		if (len < res)
>+			res = len;
>+		else {
> 			len = mm->env_end - mm->env_start;
> 			if (len > PAGE_SIZE - res)
> 				len = PAGE_SIZE - res;
>-			res += access_process_vm(task, mm->env_start, buffer+res, len, 0);
>+			res += access_process_vm(task, mm->env_start,
>+						 buffer+res, len, 0);
> 			res = strnlen(buffer, res);
> 		}
> 	}
>+
>+out_unlock:
>+	mutex_unlock(&mm->arg_lock);
>+
> out_mm:
> 	mmput(mm);
> out:
>diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
>index 84a524a..3e2a346 100644
>--- a/include/linux/mm_types.h
>+++ b/include/linux/mm_types.h
>@@ -12,6 +12,7 @@
> #include <linux/completion.h>
> #include <linux/cpumask.h>
> #include <linux/page-debug-flags.h>
>+#include <linux/mutex.h>
> #include <asm/page.h>
> #include <asm/mmu.h>
> 
>@@ -236,6 +237,7 @@ struct mm_struct {
> 	unsigned long stack_vm, reserved_vm, def_flags, nr_ptes;
> 	unsigned long start_code, end_code, start_data, end_data;
> 	unsigned long start_brk, brk, start_stack;
>+	struct mutex arg_lock;
> 	unsigned long arg_start, arg_end, env_start, env_end;
> 
> 	unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */
>diff --git a/include/linux/prctl.h b/include/linux/prctl.h
>index 9311505..da47542 100644
>--- a/include/linux/prctl.h
>+++ b/include/linux/prctl.h
>@@ -90,4 +90,7 @@
> 
> #define PR_MCE_KILL	33
> 
>+/* Set process title memory area for setproctitle() */
>+#define PR_SET_PROCTITLE_AREA 34
>+
> #endif /* _LINUX_PRCTL_H */
>diff --git a/kernel/fork.c b/kernel/fork.c
>index 4c20fff..881a6b4 100644
>--- a/kernel/fork.c
>+++ b/kernel/fork.c
>@@ -459,6 +459,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
> 	mm->cached_hole_size = ~0UL;
> 	mm_init_aio(mm);
> 	mm_init_owner(mm, p);
>+	mutex_init(&mm->arg_lock);
> 
> 	if (likely(!mm_alloc_pgd(mm))) {
> 		mm->def_flags = 0;
>diff --git a/kernel/sys.c b/kernel/sys.c
>index 255475d..bde6957 100644
>--- a/kernel/sys.c
>+++ b/kernel/sys.c
>@@ -1564,6 +1564,28 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> 			error = 0;
> 			break;
> 
>+		case PR_SET_PROCTITLE_AREA: {
>+			struct mm_struct *mm = current->mm;
>+			unsigned long addr = arg2;
>+			unsigned long len = arg3;
>+			unsigned long end = arg2 + arg3;
>+
>+			if (len > PAGE_SIZE)
>+				return -EINVAL;
>+
>+			if (addr >= end)
>+				return -EINVAL;
>+
>+			if (!access_ok(VERIFY_READ, addr, len))
>+				return -EFAULT;
>+
>+			mutex_lock(&mm->arg_lock);
>+			mm->arg_start = addr;
>+			mm->arg_end = end;
>+			mutex_unlock(&mm->arg_lock);
>+
>+			return 0;
>+		}
> 		default:
> 			error = -EINVAL;
> 			break;
>-- 
>1.6.2.5
>
>
>
>

-- 
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