[RFC PATCH 06/17] tracing: Use trace_seq_used() and seq_buf_used() instead of len

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From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>

commit 5ac48378414dccca735897c4d7f4e19987c8977c upstream.

As the seq_buf->len will soon be +1 size when there's an overflow, we
must use trace_seq_used() or seq_buf_used() methods to get the real
length. This will prevent buffer overflow issues if just the len
of the seq_buf descriptor is used to copy memory.

Link: http://lkml.kernel.org/r/20141114121911.09ba3d38@xxxxxxxxxxxxxxxxxx

Reported-by: Petr Mladek <pmladek@xxxxxxx>
[wanglong: backport to 3.10 stable
- only backport seq_buf related
]
Signed-off-by: Wang Long <long.wanglong@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/trace/seq_buf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/seq_buf.c b/kernel/trace/seq_buf.c
index 9ec5305..ce17f65 100644
--- a/kernel/trace/seq_buf.c
+++ b/kernel/trace/seq_buf.c
@@ -328,7 +328,7 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
 	if (s->len <= s->readpos)
 		return -EBUSY;
 
-	len = s->len - s->readpos;
+	len = seq_buf_used(s) - s->readpos;
 	if (cnt > len)
 		cnt = len;
 	ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);
-- 
1.8.3.4

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