linux-kernel - [PATCH AUTOSEL 5.2 72/85] stacktrace: Force USER_DS for stack_trace_save

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Date:   Fri, 26 Jul 2019 09:39:22 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Eiichi Tsukata <devel@...ukata.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joel Fernandes <joel@...lfernandes.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.2 72/85] stacktrace: Force USER_DS for stack_trace_save_user()

From: Peter Zijlstra <peterz@...radead.org>

[ Upstream commit cac9b9a4b08304f11daace03b8b48659355e44c1 ]

When walking userspace stacks, USER_DS needs to be set, otherwise
access_ok() will not function as expected.

Reported-by: Vegard Nossum <vegard.nossum@...cle.com>
Reported-by: Eiichi Tsukata <devel@...ukata.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Vegard Nossum <vegard.nossum@...cle.com>
Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Link: https://lkml.kernel.org/r/20190718085754.GM3402@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/stacktrace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 36139de0a3c4..899b726c9e98 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -226,12 +226,17 @@ unsigned int stack_trace_save_user(unsigned long *store, unsigned int size)
 		.store	= store,
 		.size	= size,
 	};
+	mm_segment_t fs;
 
 	/* Trace user stack if not a kernel thread */
 	if (!current->mm)
 		return 0;
 
+	fs = get_fs();
+	set_fs(USER_DS);
 	arch_stack_walk_user(consume_entry, &c, task_pt_regs(current));
+	set_fs(fs);
+
 	return c.len;
 }
 #endif
-- 
2.20.1