[PATCH 3.2 056/185] mm: ensure get_unmapped_area() returns higher address than mmap_min_addr

Ben Hutchings
2013-12-29T02:20:32Z

From: Akira Takeuchi <takeuchi.akr@jp.panasonic.com>

commit 2afc745f3e3079ab16c826be4860da2529054dd2 upstream.

This patch fixes the problem that get_unmapped_area() can return illegal
address and result in failing mmap(2) etc.

In case that the address higher than PAGE_SIZE is set to
/proc/sys/vm/mmap_min_addr, the address lower than mmap_min_addr can be
returned by get_unmapped_area(), even if you do not pass any virtual
address hint (i.e. the second argument).

This is because the current get_unmapped_area() code does not take into
account mmap_min_addr.

This leads to two actual problems as follows:

1. mmap(2) can fail with EPERM on the process without CAP_SYS_RAWIO,
although any illegal parameter is not passed.

2. The bottom-up search path after the top-down search might not work in
arch_get_unmapped_area_topdown().

Note: The first and third chunk of my patch, which changes "len" check,
are for more precise check using mmap_min_addr, and not for solving the
above problem.

[How to reproduce]

--- test.c -------------------------------------------------
#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/errno.h>

int main(int argc, char *argv[])
{
void *ret = NULL, *last_map;
size_t pagesize = sysconf(_SC_PAGESIZE);

do {
last_map = ret;
ret = mmap(0, pagesize, PROT_NONE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
// printf("ret=%p\n", ret);
} while (ret != MAP_FAILED);

if (errno != ENOMEM) {
printf("ERR: unexpected errno: %d (last map=%p)\n",
errno, last_map);
}

return 0;
}
---------------------------------------------------------------

$ gcc -m32 -o test test.c
$ sudo sysctl -w vm.mmap_min_addr=65536
vm.mmap_min_addr = 65536
$ ./test (run as non-priviledge user)
ERR: unexpected errno: 1 (last map=0x10000)

Signed-off-by: Akira Takeuchi <takeuchi.akr@jp.panasonic.com>
Signed-off-by: Kiyoshi Owada <owada.kiyoshi@jp.panasonic.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2:
As we do not have vm_unmapped_area(), make arch_get_unmapped_area_topdown()
calculate the lower limit for the new area's end address and then compare
addresses with this instead of with len. In the process, fix an off-by-one
error which could result in returning 0 if mm->mmap_base == len.]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1368,7 +1368,7 @@ arch_get_unmapped_area(struct file *filp
struct vm_area_struct *vma;
unsigned long start_addr;

- if (len > TASK_SIZE)
+ if (len > TASK_SIZE - mmap_min_addr)
return -ENOMEM;

if (flags & MAP_FIXED)
@@ -1377,7 +1377,7 @@ arch_get_unmapped_area(struct file *filp
if (addr) {
addr = PAGE_ALIGN(addr);
vma = find_vma(mm, addr);
- if (TASK_SIZE - len >= addr &&
+ if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
(!vma || addr + len <= vma->vm_start))
return addr;
}
@@ -1442,9 +1442,10 @@ arch_get_unmapped_area_topdown(struct fi
struct vm_area_struct *vma;
struct mm_struct *mm = current->mm;
unsigned long addr = addr0;
+ unsigned long low_limit = max(PAGE_SIZE, mmap_min_addr);

/* requested length too big for entire address space */
- if (len > TASK_SIZE)
+ if (len > TASK_SIZE - mmap_min_addr)
return -ENOMEM;

if (flags & MAP_FIXED)
@@ -1454,7 +1455,7 @@ arch_get_unmapped_area_topdown(struct fi
if (addr) {
addr = PAGE_ALIGN(addr);
vma = find_vma(mm, addr);
- if (TASK_SIZE - len >= addr &&
+ if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
(!vma || addr + len <= vma->vm_start))
return addr;
}
@@ -1469,14 +1470,14 @@ arch_get_unmapped_area_topdown(struct fi
addr = mm->free_area_cache;

/* make sure it can fit in the remaining address space */
- if (addr > len) {
+ if (addr >= low_limit + len) {
vma = find_vma(mm, addr-len);
if (!vma || addr <= vma->vm_start)
/* remember the address as a hint for next time */
return (mm->free_area_cache = addr-len);
}

- if (mm->mmap_base < len)
+ if (mm->mmap_base < low_limit + len)
goto bottomup;

addr = mm->mmap_base-len;
@@ -1498,7 +1499,7 @@ arch_get_unmapped_area_topdown(struct fi

/* try just below the current vma->vm_start */
addr = vma->vm_start-len;
- } while (len < vma->vm_start);
+ } while (vma->vm_start >= low_limit + len);

bottomup:
/*