From 0a1d52994d440e21def1c2174932410b4f2a98a1 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 27 Feb 2019 21:29:52 +0100 Subject: 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 Signed-off-by: Linus Torvalds Signed-off-by: Adrian Stratulat Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0a1d52994d440e21def1c2174932410b4f2a98a1] CVE: CVE-2019-9213 --- mm/mmap.c | 7 +++---- 1 file 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; -- cgit 1.2-0.3.lf.el7