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Date: Tue, 3 Nov 2009 17:47:03 +0800
From: Américo Wang <xiyou.wangcong@...il.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Timo Sirainen <tss@....fi>, Bryan Donlan <bdonlan@...il.com>,
Ulrich Drepper <drepper@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-api@...r.kernel.org
Subject: Re: [PATCH v4] Added PR_SET_PROCTITLE_AREA option for prctl()
On Sun, Nov 01, 2009 at 09:16:27PM +0900, KOSAKI Motohiro wrote:
>
>ChangeLog
> v3 -> v4
> - Use mutex instead seq_lock as akpm requested.
>
>========================================
>
>From: Timo Sirainen <tss@....fi>
Please see my comments below.
>
>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@...il.com>
>Cc: Ulrich Drepper <drepper@...hat.com>
>Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>Signed-off-by: Timo Sirainen <tss@....fi>
>---
> 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..434ea13 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;
Is this safe? You're assigning a user-space pointer to kernel space...
Don't we need copy_from_user()?
>+ mm->arg_end = addr + len;
Since you already have 'end', no need to caculate this again. :)
>+ mutex_unlock(&mm->arg_lock);
>+
>+ return 0;
>+ }
> default:
> error = -EINVAL;
> break;
--
Live like a child, think like the god.
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