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Commit 3c77f845 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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exec: make argv/envp memory visible to oom-killer 

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: default avatarBrad Spengler <spender@grsecurity.net>
Reviewed-and-discussed-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: stable@kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 37a09f07

fs/exec.c

+30 −2
Original line number Diff line number Diff line
@@ -164,6 +164,25 @@ 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)

{
@@ -186,6 +205,8 @@ 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
@@ -276,6 +297,10 @@ 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)

{
@@ -1003,6 +1028,7 @@ 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;
@@ -1426,8 +1452,10 @@ int do_execve(const char * filename, 
	return retval;



out:

	if (bprm->mm)

	if (bprm->mm) {

		acct_arg_size(bprm, 0);

		mmput(bprm->mm);

	}



out_file:

	if (bprm->file) {

include/linux/binfmts.h

+1 −0
Original line number Diff line number Diff line
@@ -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];