From: "Steven Rostedt (VMware)" <[email protected]> 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. Signed-off-by: Steven Rostedt (VMware) <[email protected]> --- kernel/trace/ftrace.c | 28 +++++++++++++++++++++++----- 1 file changed, 23 insertions(+), 5 deletions(-) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 0233c8cb45f4..b3a4896ef78a 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -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); -- 2.10.2
