linux-kernel - [PATCH 4.9 071/130] arm64/ptrace: Preserve previous registers for short regset write

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Date:   Tue, 24 Jan 2017 08:55:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Martin <Dave.Martin@....com>,
        Will Deacon <Will.Deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: [PATCH 4.9 071/130] arm64/ptrace: Preserve previous registers for short regset write - 2

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

------------------

From: Dave Martin <Dave.Martin@....com>

commit 9dd73f72f218320c6c90da5f834996e7360dc227 upstream.

Ensure that if userspace supplies insufficient data to
PTRACE_SETREGSET to fill all the registers, the thread's old
registers are preserved.

Fixes: 766a85d7bc5d ("arm64: ptrace: add NT_ARM_SYSTEM_CALL regset")
Signed-off-by: Dave Martin <Dave.Martin@....com>
Acked-by: Will Deacon <Will.Deacon@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm64/kernel/ptrace.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -676,7 +676,8 @@ static int system_call_set(struct task_s
 			   unsigned int pos, unsigned int count,
 			   const void *kbuf, const void __user *ubuf)
 {
-	int syscallno, ret;
+	int syscallno = task_pt_regs(target)->syscallno;
+	int ret;
 
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &syscallno, 0, -1);
 	if (ret)