[PATCH 4.2 099/110] um: Fix kernel mode fault condition

From: Greg Kroah-Hartman
Date: Fri Nov 06 2015 - 15:28:45 EST

4.2-stable review patch. If anyone has any objections, please let me know.


From: Richard Weinberger <richard@xxxxxx>

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@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/um/kernel/trap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -220,7 +220,7 @@ unsigned long segv(struct faultinfo fi,
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);

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