um: Fix kernel mode fault condition

We have to exclude memory locations <= PAGE_SIZE from
the condition and let the kernel mode fault path catch it.
Otherwise a kernel NULL pointer exception will be reported
as a kernel user space access.

Fixes: d2313084e2c (um: Catch unprotected user memory access)
Signed-off-by: Richard Weinberger <richard@nod.at>

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index d8a9fce6ee2e5b10a63405654c3958c7361951fe..98783dd0fa2ea697a50cb65afb661aa7f7bf0322 100644 (file)
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -220,7 +220,7 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
                show_regs(container_of(regs, struct pt_regs, regs));
                panic("Segfault with no mm");
        }
-       else if (!is_user && address < TASK_SIZE) {
+       else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
                show_regs(container_of(regs, struct pt_regs, regs));
                panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
                       address, ip);