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exec: make argv/envp memory visible to oom-killer

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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 <[email protected]>
Reviewed-and-discussed-by: KOSAKI Motohiro <[email protected]>
Signed-off-by: Oleg Nesterov <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Oleg Nesterov 2010-11-30 20:55:34 +01:00 • committed by Linus Torvalds
commit 3c77f84572
2 changed files with 31 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

32
fs/exec.c
View file

@ -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)
mmput (bprm->mm);
if (bprm->mm) {
acct_arg_size(bprm, 0);
mmput(bprm->mm);
}
out_file:
if (bprm->file) {