[PATCH 3.10 066/173] mm: ensure get_unmapped_area() returns higher address than mmap_min_addr

Greg Kroah-Hartman
2013-12-02T19:13:37Z

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/mmap.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1853,7 +1853,7 @@ arch_get_unmapped_area(struct file *filp
struct vm_area_struct *vma;
struct vm_unmapped_area_info info;

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

if (flags & MAP_FIXED)
@@ -1862,7 +1862,7 @@ 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;
}
@@ -1901,7 +1901,7 @@ arch_get_unmapped_area_topdown(struct fi
struct vm_unmapped_area_info info;

/* 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)
@@ -1911,14 +1911,14 @@ 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;
}

info.flags = VM_UNMAPPED_AREA_TOPDOWN;
info.length = len;
- info.low_limit = PAGE_SIZE;
+ info.low_limit = max(PAGE_SIZE, mmap_min_addr);
info.high_limit = mm->mmap_base;
info.align_mask = 0;
addr = vm_unmapped_area(&info);