| From 0a1d52994d440e21def1c2174932410b4f2a98a1 Mon Sep 17 00:00:00 2001 |
| From: Jann Horn <jannh@google.com> |
| Date: Wed, 27 Feb 2019 21:29:52 +0100 |
| Subject: mm: enforce min addr even if capable() in expand_downwards() |
| |
| From: Jann Horn <jannh@google.com> |
| |
| commit 0a1d52994d440e21def1c2174932410b4f2a98a1 upstream. |
| |
| security_mmap_addr() does a capability check with current_cred(), but |
| we can reach this code from contexts like a VFS write handler where |
| current_cred() must not be used. |
| |
| This can be abused on systems without SMAP to make NULL pointer |
| dereferences exploitable again. |
| |
| Fixes: 8869477a49c3 ("security: protect from stack expansion into low vm addresses") |
| Cc: stable@kernel.org |
| Signed-off-by: Jann Horn <jannh@google.com> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| mm/mmap.c | 7 +++---- |
| 1 file changed, 3 insertions(+), 4 deletions(-) |
| |
| --- a/mm/mmap.c |
| +++ b/mm/mmap.c |
| @@ -2391,12 +2391,11 @@ int expand_downwards(struct vm_area_stru |
| { |
| struct mm_struct *mm = vma->vm_mm; |
| struct vm_area_struct *prev; |
| - int error; |
| + int error = 0; |
| |
| address &= PAGE_MASK; |
| - error = security_mmap_addr(address); |
| - if (error) |
| - return error; |
| + if (address < mmap_min_addr) |
| + return -EPERM; |
| |
| /* Enforce stack_guard_gap */ |
| prev = vma->vm_prev; |