Patch "powerpc/signal: Properly handle return value from uprobe_deny_signal()" has been added to the 4.4-stable tree

Patch "powerpc/signal: Properly handle return value from uprobe_deny_signal()" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    powerpc/signal: Properly handle return value from uprobe_deny_signal()

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-signal-properly-handle-return-value-from-uprobe_deny_signal.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 46725b17f1c6c815a41429259b3f070c01e71bc1 Mon Sep 17 00:00:00 2001
From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Date: Thu, 31 Aug 2017 21:55:57 +0530
Subject: powerpc/signal: Properly handle return value from uprobe_deny_signal()

From: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>

commit 46725b17f1c6c815a41429259b3f070c01e71bc1 upstream.

When a uprobe is installed on an instruction that we currently do not
emulate, we copy the instruction into a xol buffer and single step
that instruction. If that instruction generates a fault, we abort the
single stepping before invoking the signal handler. Once the signal
handler is done, the uprobe trap is hit again since the instruction is
retried and the process repeats.

We use uprobe_deny_signal() to detect if the xol instruction triggered
a signal. If so, we clear TIF_SIGPENDING and set TIF_UPROBE so that the
signal is not handled until after the single stepping is aborted. In
this case, uprobe_deny_signal() returns true and get_signal() ends up
returning 0. However, in do_signal(), we are not looking at the return
value, but depending on ksig.sig for further action, all with an
uninitialized ksig that is not touched in this scenario. Fix the same
by initializing ksig.sig to 0.

Fixes: 129b69df9c90 ("powerpc: Use get_signal() signal_setup_done()")
Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -102,7 +102,7 @@ static void check_syscall_restart(struct
 static void do_signal(struct pt_regs *regs)
 {
 	sigset_t *oldset = sigmask_to_save();
-	struct ksignal ksig;
+	struct ksignal ksig = { .sig = 0 };
 	int ret;
 	int is32 = is_32bit_task();
 


Patches currently in stable-queue which might be from naveen.n.rao@linux.vnet.ibm.com are

queue-4.4/powerpc-signal-properly-handle-return-value-from-uprobe_deny_signal.patch