[PATCH 5.2 065/131] stacktrace: Force USER_DS for stack_trace_save_user()

[Greg Kroah-Hartman]

[ 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@xxxxxxxxxx>
Reported-by: Eiichi Tsukata <devel@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190718085754.GM3402@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/stacktrace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 36139de0a3c4b..899b726c9e98f 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