um: Fix kernel mode fault condition

commit 56b88a3bf97a39d3f4f010509917b76a865a6dc8 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 557232f758b61efe00462df9766f5a16e08ebbd3..5610b185d1e9a1707162878772c6a462e2474f7b 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);