linux-kernel - [PATCH 1/5] ptrace: don't modify flags on PTRACE

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Message-Id: <1328884991-23889-2-git-send-email-vda.linux@googlemail.com>
Date:	Fri, 10 Feb 2012 15:43:07 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Pedro Alves <palves@...hat.com>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	linux-kernel@...r.kernel.org
Cc:	Denys Vlasenko <vda.linux@...glemail.com>
Subject: [PATCH 1/5] ptrace: don't modify flags on PTRACE_SETOPTIONS failure

On ptrace(PTRACE_SETOPTIONS, pid, 0, <opts>), we used to set
those option bits which are known, and then fail with -EINVAL
if there are some unknown bits in <opts>.

This in inconsistent with typical error handling, which
does not change any state if input is invalid.

This patch changes PTRACE_SETOPTIONS behavior so that
in this case, we return -EINVAL and don't change any bits
in task->ptrace.

It's very unlikely that there is userspace code in the wild which
will be affected by this change: it should have the form

    ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_BOGUSOPT)

where PTRACE_O_BOGUSOPT is a constant unknown to the kernel.
But kernel headers, naturally, don't contain any
PTRACE_O_BOGUSOPTs, thus the only way userspace can use one
if it defines one itself. I can't see why anyone would do such
a thing deliberately.

Signed-off-by: Denys Vlasenko <vda.linux@...glemail.com>
Acked-by: Tejun Heo <tj@...nel.org>
---
 kernel/ptrace.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 00ab2ca..273f56e 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -528,6 +528,9 @@ int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long ds
 
 static int ptrace_setoptions(struct task_struct *child, unsigned long data)
 {
+	if (data & ~(unsigned long)PTRACE_O_MASK)
+		return -EINVAL;
+
 	child->ptrace &= ~PT_TRACE_MASK;
 
 	if (data & PTRACE_O_TRACESYSGOOD)
@@ -551,7 +554,7 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data)
 	if (data & PTRACE_O_TRACEEXIT)
 		child->ptrace |= PT_TRACE_EXIT;
 
-	return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
+	return 0;
 }
 
 static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
-- 
1.7.7.6

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