[ 05/82] mm/fork: fix overflow in vma length when copying mmap on clone

From: Greg KH
Date: Thu Jun 07 2012 - 00:15:46 EST


3.4-stable review patch. If anyone has any objections, please let me know.

------------------

From: Siddhesh Poyarekar <siddhesh.poyarekar@xxxxxxxxx>

commit 7edc8b0ac16cbaed7cb4ea4c6b95ce98d2997e84 upstream.

The vma length in dup_mmap is calculated and stored in a unsigned int,
which is insufficient and hence overflows for very large maps (beyond
16TB). The following program demonstrates this:

#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>

#define GIG 1024 * 1024 * 1024L
#define EXTENT 16393

int main(void)
{
int i, r;
void *m;
char buf[1024];

for (i = 0; i < EXTENT; i++) {
m = mmap(NULL, (size_t) 1 * 1024 * 1024 * 1024L,
PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);

if (m == (void *)-1)
printf("MMAP Failed: %d\n", m);
else
printf("%d : MMAP returned %p\n", i, m);

r = fork();

if (r == 0) {
printf("%d: successed\n", i);
return 0;
} else if (r < 0)
printf("FORK Failed: %d\n", r);
else if (r > 0)
wait(NULL);
}
return 0;
}

Increase the storage size of the result to unsigned long, which is
sufficient for storing the difference between addresses.

Signed-off-by: Siddhesh Poyarekar <siddhesh.poyarekar@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
kernel/fork.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -356,7 +356,8 @@ static int dup_mmap(struct mm_struct *mm
}
charge = 0;
if (mpnt->vm_flags & VM_ACCOUNT) {
- unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
+ unsigned long len;
+ len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
goto fail_nomem;
charge = len;


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