From de23c77fdbea24bbb52ef7c2e4dd3c027953cac9 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 27 Feb 2019 21:29:52 +0100 Subject: [PATCH] mm: enforce min addr even if capable() in expand_downwards() 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") Signed-off-by: Jann Horn Signed-off-by: Linus Torvalds Signed-off-by: Ben Hutchings --- mm/mmap.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 0da3ca75e174..7598c2598f72 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2256,12 +2256,11 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address) { 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;