[ARM] 3030/2: fix permission check in the obscur cmpxchg syscall
Patch from Nicolas Pitre
Quoting RMK:
|pte_write() just says that the page _may_ be writable. It doesn't say
|that the MMU is programmed to allow writes. If pte_dirty() doesn't
|return true, that means that the page is _not_ writable from userspace.
|If you write to it from kernel mode (without using put_user) you'll
|bypass the MMU read-only protection and may end up writing to a page
|owned by two separate processes.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 03924bc..d566d5f 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -506,7 +506,7 @@
if (!pmd_present(*pmd))
goto bad_access;
pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
- if (!pte_present(*pte) || !pte_write(*pte)) {
+ if (!pte_present(*pte) || !pte_dirty(*pte)) {
pte_unmap_unlock(pte, ptl);
goto bad_access;
}
