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authorJann Horn <jannh@google.com>2019-02-27 21:29:52 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2019-02-27 17:27:02 -0800
commit0a1d52994d440e21def1c2174932410b4f2a98a1 (patch)
tree0674c4cb793d0402ce24061f8db61d04024d1a88 /mm/mmap.c
parent7d762d69145a54d169f58e56d6dac57a5508debc (diff)
downloadlinux-0a1d52994d440e21def1c2174932410b4f2a98a1.tar.bz2
mm: enforce min addr even if capable() in expand_downwards()
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>
Diffstat (limited to 'mm/mmap.c')
-rw-r--r--mm/mmap.c7
1 files changed, 3 insertions, 4 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index f901065c4c64..fc1809b1bed6 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2426,12 +2426,11 @@ int expand_downwards(struct vm_area_struct *vma,
{
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;