[PATCH] GFS2: Fix unsafe dereference in dump_holder()

[Tetsuo Handa]

>From efee681e4ca6152d9549a50e93ca932b00f03014 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Tue, 24 Dec 2013 18:04:43 +0900
Subject: [PATCH] GFS2: Fix unsafe dereference in dump_holder()

Since we are not in RCU nor tasklist_lock held, we need to grab a reference on
the returned task_struct. Use get_pid_task()/get_task_comm() to safely read the
target task's comm name.

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 fs/gfs2/glock.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index c8420f7..7bda965 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1654,15 +1654,22 @@ static int dump_holder(struct seq_file *seq, const struct gfs2_holder *gh)
 {
 	struct task_struct *gh_owner = NULL;
 	char flags_buf[32];
+	char name[TASK_COMM_LEN];
 
 	if (gh->gh_owner_pid)
-		gh_owner = pid_task(gh->gh_owner_pid, PIDTYPE_PID);
+		gh_owner = get_pid_task(gh->gh_owner_pid, PIDTYPE_PID);
+	if (gh_owner) {
+		get_task_comm(name, gh_owner);
+		put_task_struct(gh_owner);
+	} else {
+		strlcpy(name, "(ended)", sizeof(name));
+	}
 	gfs2_print_dbg(seq, " H: s:%s f:%s e:%d p:%ld [%s] %pS\n",
 		       state2str(gh->gh_state),
 		       hflags2str(flags_buf, gh->gh_flags, gh->gh_iflags),
 		       gh->gh_error,
 		       gh->gh_owner_pid ? (long)pid_nr(gh->gh_owner_pid) : -1,
-		       gh_owner ? gh_owner->comm : "(ended)",
+		       name,
 		       (void *)gh->gh_ip);
 	return 0;
 }
-- 
1.7.1
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