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ftrace: Do not hold references of ftrace_graph_{notrace_}hash out of graph_lock

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The hashs ftrace_graph_hash and ftrace_graph_notrace_hash are modified
within the graph_lock being held. Holding a pointer to them and passing them
along can lead to a use of a stale pointer (fgd->hash). Move assigning the
pointer and its use to within the holding of the lock. Note, it's an
rcu_sched protected data, and other instances of referencing them are done
with preemption disabled. But the file manipuation code must be protected by
the lock.

The fgd->hash pointer is set to NULL when the lock is being released.

Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2017-02-02 20:16:29 -05:00
parent 0e684b6578
commit 649b988b12
1 changed files with 23 additions and 5 deletions
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28
kernel/trace/ftrace.c
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@ -4616,6 +4616,13 @@ static void *g_start(struct seq_file *m, loff_t *pos)
mutex_lock(&graph_lock);
if (fgd->type == GRAPH_FILTER_FUNCTION)
fgd->hash = rcu_dereference_protected(ftrace_graph_hash,
lockdep_is_held(&graph_lock));
else
fgd->hash = rcu_dereference_protected(ftrace_graph_notrace_hash,
lockdep_is_held(&graph_lock));
/* Nothing, tell g_show to print all functions are enabled */
if (ftrace_hash_empty(fgd->hash) && !*pos)
return FTRACE_GRAPH_EMPTY;
@ -4695,6 +4702,14 @@ __ftrace_graph_open(struct inode *inode, struct file *file,
out:
fgd->new_hash = new_hash;
/*
* All uses of fgd->hash must be taken with the graph_lock
* held. The graph_lock is going to be released, so force
* fgd->hash to be reinitialized when it is taken again.
*/
fgd->hash = NULL;
return ret;
}
@ -4713,7 +4728,8 @@ ftrace_graph_open(struct inode *inode, struct file *file)
mutex_lock(&graph_lock);
fgd->hash = ftrace_graph_hash;
fgd->hash = rcu_dereference_protected(ftrace_graph_hash,
lockdep_is_held(&graph_lock));
fgd->type = GRAPH_FILTER_FUNCTION;
fgd->seq_ops = &ftrace_graph_seq_ops;
@ -4740,7 +4756,8 @@ ftrace_graph_notrace_open(struct inode *inode, struct file *file)
mutex_lock(&graph_lock);
fgd->hash = ftrace_graph_notrace_hash;
fgd->hash = rcu_dereference_protected(ftrace_graph_notrace_hash,
lockdep_is_held(&graph_lock));
fgd->type = GRAPH_FILTER_NOTRACE;
fgd->seq_ops = &ftrace_graph_seq_ops;
@ -4859,17 +4876,18 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
ret = ftrace_graph_set_hash(fgd->new_hash,
parser.buffer);
old_hash = fgd->hash;
new_hash = __ftrace_hash_move(fgd->new_hash);
if (!new_hash)
ret = -ENOMEM;
if (fgd->type == GRAPH_FILTER_FUNCTION) {
old_hash = rcu_dereference_protected(ftrace_graph_hash,
lockdep_is_held(&graph_lock));
rcu_assign_pointer(ftrace_graph_hash, new_hash);
fgd->hash = ftrace_graph_hash;
} else {
old_hash = rcu_dereference_protected(ftrace_graph_notrace_hash,
lockdep_is_held(&graph_lock));
rcu_assign_pointer(ftrace_graph_notrace_hash, new_hash);
fgd->hash = ftrace_graph_notrace_hash;
}
mutex_unlock(&graph_lock);