lkml.org 
[lkml]   [2011]   [Apr]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[34-longterm 136/209] exec: make argv/envp memory visible to oom-killer
Date
From: Oleg Nesterov <oleg@redhat.com>

=====================================================================
| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|
=====================================================================

commit 3c77f845722158206a7209c45ccddc264d19319c upstream

Brad Spengler published a local memory-allocation DoS that
evades the OOM-killer (though not the virtual memory RLIMIT):
http://www.grsecurity.net/~spender/64bit_dos.c

execve()->copy_strings() can allocate a lot of memory, but
this is not visible to oom-killer, nobody can see the nascent
bprm->mm and take it into account.

With this patch get_arg_page() increments current's MM_ANONPAGES
counter every time we allocate the new page for argv/envp. When
do_execve() succeds or fails, we change this counter back.

Technically this is not 100% correct, we can't know if the new
page is swapped out and turn MM_ANONPAGES into MM_SWAPENTS, but
I don't think this really matters and everything becomes correct
once exec changes ->mm or fails.

Reported-by: Brad Spengler <spender@grsecurity.net>
Reviewed-and-discussed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
fs/exec.c | 32 ++++++++++++++++++++++++++++++--
include/linux/binfmts.h | 1 +
2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index afd9977..8d4912f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -158,6 +158,25 @@ out:

#ifdef CONFIG_MMU

+static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
+{
+ struct mm_struct *mm = current->mm;
+ long diff = (long)(pages - bprm->vma_pages);
+
+ if (!mm || !diff)
+ return;
+
+ bprm->vma_pages = pages;
+
+#ifdef SPLIT_RSS_COUNTING
+ add_mm_counter(mm, MM_ANONPAGES, diff);
+#else
+ spin_lock(&mm->page_table_lock);
+ add_mm_counter(mm, MM_ANONPAGES, diff);
+ spin_unlock(&mm->page_table_lock);
+#endif
+}
+
static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
int write)
{
@@ -180,6 +199,8 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
struct rlimit *rlim;

+ acct_arg_size(bprm, size / PAGE_SIZE);
+
/*
* We've historically supported up to 32 pages (ARG_MAX)
* of argument strings even with small stacks
@@ -269,6 +290,10 @@ static bool valid_arg_len(struct linux_binprm *bprm, long len)

#else

+static inline void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
+{
+}
+
static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
int write)
{
@@ -987,6 +1012,7 @@ int flush_old_exec(struct linux_binprm * bprm)
/*
* Release all of the old mmap stuff
*/
+ acct_arg_size(bprm, 0);
retval = exec_mmap(bprm->mm);
if (retval)
goto out;
@@ -1411,8 +1437,10 @@ int do_execve(char * filename,
return retval;

out:
- if (bprm->mm)
- mmput (bprm->mm);
+ if (bprm->mm) {
+ acct_arg_size(bprm, 0);
+ mmput(bprm->mm);
+ }

out_file:
if (bprm->file) {
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index c809e28..39798c6 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -29,6 +29,7 @@ struct linux_binprm{
char buf[BINPRM_BUF_SIZE];
#ifdef CONFIG_MMU
struct vm_area_struct *vma;
+ unsigned long vma_pages;
#else
# define MAX_ARG_PAGES 32
struct page *page[MAX_ARG_PAGES];
--
1.7.4.4


\
 
 \ /
  Last update: 2011-04-14 20:17    [W:0.713 / U:0.060 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site