The patch titled
mm: install_special_mapping skips security_file_mmap() check
has been added to the -mm tree. Its filename is
mm-install_special_mapping-skips-security_file_mmap-check.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: mm: install_special_mapping skips security_file_mmap() check
From: Tavis Ormandy <taviso@xxxxxxxxxxxxx>
The install_special_mapping routine (used, for example, to setup the vdso)
skips the security check before insert_vm_struct, allowing a local
attacker to bypass the mmap_min_addr security restriction by limiting the
available pages for special mappings. bprm_mm_init() also skips the
check, although I don't think this can be used to bypass any restrictions,
I don't see any reason not to have the security check.
$ uname -m
x86_64
$ cat /proc/sys/vm/mmap_min_addr
65536
$ cat install_special_mapping.s
section .bss
resb BSS_SIZE
section .text
global _start
_start:
mov eax, __NR_pause
int 0x80
$ nasm -D__NR_pause=29 -DBSS_SIZE=0xfffed000 -f elf -o install_special_mapping.o install_special_mapping.s
$ ld -m elf_i386 -Ttext=0x10000 -Tbss=0x11000 -o install_special_mapping install_special_mapping.o
$ ./install_special_mapping &
[1] 14303
$ cat /proc/14303/maps
0000f000-00010000 r-xp 00000000 00:00 0 [vdso]
00010000-00011000 r-xp 00001000 00:19 2453665 /home/taviso/install_special_mapping
00011000-ffffe000 rwxp 00000000 00:00 0 [stack]
It's worth noting that Red Hat are shipping with mmap_min_addr set to 4096.
Signed-off-by: Tavis Ormandy <taviso@xxxxxxxxxx>
Acked-by: Kees Cook <kees.cook@xxxxxxxxxxxxx>
Acked-by: Robert Swiecki <swiecki@xxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Randy Dunlap <randy.dunlap@xxxxxxxxxx>
Cc: Greg KH <greg@xxxxxxxxx>
Cc: Eugene Teo <eugene@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 7 +++++++
mm/mmap.c | 5 +++++
2 files changed, 12 insertions(+)
diff -puN fs/exec.c~mm-install_special_mapping-skips-security_file_mmap-check fs/exec.c
--- a/fs/exec.c~mm-install_special_mapping-skips-security_file_mmap-check
+++ a/fs/exec.c
@@ -275,7 +275,14 @@ static int __bprm_mm_init(struct linux_b
vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
INIT_LIST_HEAD(&vma->anon_vma_chain);
+
+ err = security_file_mmap(NULL, 0, 0, 0, vma->vm_start, 1);
+
+ if (err)
+ goto err;
+
err = insert_vm_struct(mm, vma);
+
if (err)
goto err;
diff -puN mm/mmap.c~mm-install_special_mapping-skips-security_file_mmap-check mm/mmap.c
--- a/mm/mmap.c~mm-install_special_mapping-skips-security_file_mmap-check
+++ a/mm/mmap.c
@@ -2479,6 +2479,11 @@ int install_special_mapping(struct mm_st
vma->vm_ops = &special_mapping_vmops;
vma->vm_private_data = pages;
+ if (security_file_mmap(NULL, 0, 0, 0, vma->vm_start, 1)) {
+ kmem_cache_free(vm_area_cachep, vma);
+ return -EPERM;
+ }
+
if (unlikely(insert_vm_struct(mm, vma))) {
kmem_cache_free(vm_area_cachep, vma);
return -ENOMEM;
_
Patches currently in -mm which might be from taviso@xxxxxxxxxxxxx are
mm-install_special_mapping-skips-security_file_mmap-check.patch
mm-install_special_mapping-skips-security_file_mmap-check-fix.patch
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