[PATCH 6/6] GFS2: Fix unsafe dereference in dump_holder()

From: Steven Whitehouse
Date: Thu Jan 02 2014 - 07:29:22 EST

From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

GLOCK_BUG_ON() might call this function without RCU read lock. Make sure that
RCU read lock is held when using task_struct returned from pid_task().

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Whitehouse <swhiteho@xxxxxxxxxx>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index c8420f7..6f7a47c 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1655,6 +1655,7 @@ static int dump_holder(struct seq_file *seq, const struct gfs2_holder *gh)
struct task_struct *gh_owner = NULL;
char flags_buf[32];

+ rcu_read_lock();
if (gh->gh_owner_pid)
gh_owner = pid_task(gh->gh_owner_pid, PIDTYPE_PID);
gfs2_print_dbg(seq, " H: s:%s f:%s e:%d p:%ld [%s] %pS\n",
@@ -1664,6 +1665,7 @@ static int dump_holder(struct seq_file *seq, const struct gfs2_holder *gh)
gh->gh_owner_pid ? (long)pid_nr(gh->gh_owner_pid) : -1,
gh_owner ? gh_owner->comm : "(ended)",
(void *)gh->gh_ip);
+ rcu_read_unlock();
return 0;


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