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Date: Fri, 14 Nov 2014 15:56:12 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Petr Mladek <pmladek@...e.cz>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Jiri Kosina <jkosina@...e.cz>
Subject: Re: [RFC][PATCH 17/23 v4] tracing: Have seq_buf use full buffer
On Fri, 14 Nov 2014 12:30:01 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:
> > Hmm, we should not apply this patch before we fix all other locations
> > accessing seq.len. We need to make sure that they do not access
> > outside of the buffer when seq.len = seq.size + 1.
> >
> > See my comments for "[RFC][PATCH 13/23 v4] tracing: Create seq_buf
> > layer in trace_seq"
>
> I agree. As I replied there, I'll add a patch before this gets applied
> (right after seq_buf_left() is introduced), that will fix those issues.
I made the move of seq_buf_used() before the full buffer usage patch,
and here's a patch I added.
I'll be posting a v5 with all these changes too, but this may make it
easier to review:
-- Steve
>From a43da42e939ba41a32c7ea83793cef9c2360ec1a Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
Date: Fri, 14 Nov 2014 15:49:41 -0500
Subject: [PATCH] tracing: Use trace_seq_used() and seq_buf_used() instead of
len
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@gandalf.local.home
Reported-by: Petr Mladek <pmladek@...e.cz>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
include/linux/trace_seq.h | 20 +++++++++++++++-
kernel/trace/trace.c | 44 ++++++++++++++++++++++++------------
kernel/trace/trace_events.c | 9 +++++---
kernel/trace/trace_functions_graph.c | 5 +++-
kernel/trace/trace_seq.c | 2 +-
5 files changed, 59 insertions(+), 21 deletions(-)
diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index 85d37106be3d..cfaf5a1d4bad 100644
--- a/include/linux/trace_seq.h
+++ b/include/linux/trace_seq.h
@@ -24,6 +24,24 @@ trace_seq_init(struct trace_seq *s)
}
/**
+ * trace_seq_used - amount of actual data written to buffer
+ * @s: trace sequence descriptor
+ *
+ * Returns the amount of data written to the buffer.
+ *
+ * IMPORTANT!
+ *
+ * Use this instead of @s->seq.len if you need to pass the amount
+ * of data from the buffer to another buffer (userspace, or what not).
+ * The @s->seq.len on overflow is bigger than the buffer size and
+ * using it can cause access to undefined memory.
+ */
+static inline int trace_seq_used(struct trace_seq *s)
+{
+ return seq_buf_used(&s->seq);
+}
+
+/**
* trace_seq_buffer_ptr - return pointer to next location in buffer
* @s: trace sequence descriptor
*
@@ -35,7 +53,7 @@ trace_seq_init(struct trace_seq *s)
static inline unsigned char *
trace_seq_buffer_ptr(struct trace_seq *s)
{
- return s->buffer + s->seq.len;
+ return s->buffer + seq_buf_used(&s->seq);
}
/**
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7d7a07e9b9e9..9f1ffc707f3b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -944,10 +944,10 @@ static ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt)
{
int len;
- if (s->seq.len <= s->seq.readpos)
+ if (trace_seq_used(s) <= s->seq.readpos)
return -EBUSY;
- len = s->seq.len - s->seq.readpos;
+ len = trace_seq_used(s) - s->seq.readpos;
if (cnt > len)
cnt = len;
memcpy(buf, s->buffer + s->seq.readpos, cnt);
@@ -4514,18 +4514,18 @@ waitagain:
trace_access_lock(iter->cpu_file);
while (trace_find_next_entry_inc(iter) != NULL) {
enum print_line_t ret;
- int len = iter->seq.seq.len;
+ int save_len = iter->seq.seq.len;
ret = print_trace_line(iter);
if (ret == TRACE_TYPE_PARTIAL_LINE) {
/* don't print partial lines */
- iter->seq.seq.len = len;
+ iter->seq.seq.len = save_len;
break;
}
if (ret != TRACE_TYPE_NO_CONSUME)
trace_consume(iter);
- if (iter->seq.seq.len >= cnt)
+ if (trace_seq_used(&iter->seq) >= cnt)
break;
/*
@@ -4541,7 +4541,7 @@ waitagain:
/* Now copy what we have to the user */
sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
- if (iter->seq.seq.readpos >= iter->seq.seq.len)
+ if (iter->seq.seq.readpos >= trace_seq_used(&iter->seq))
trace_seq_init(&iter->seq);
/*
@@ -4575,20 +4575,33 @@ static size_t
tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
{
size_t count;
+ int save_len;
int ret;
/* Seq buffer is page-sized, exactly what we need. */
for (;;) {
- count = iter->seq.seq.len;
+ save_len = iter->seq.seq.len;
ret = print_trace_line(iter);
- count = iter->seq.seq.len - count;
- if (rem < count) {
- rem = 0;
- iter->seq.seq.len -= count;
+
+ if (trace_seq_has_overflowed(&iter->seq)) {
+ iter->seq.seq.len = save_len;
break;
}
+
+ /*
+ * This should not be hit, because it should only
+ * be set if the iter->seq overflowed. But check it
+ * anyway to be safe.
+ */
if (ret == TRACE_TYPE_PARTIAL_LINE) {
- iter->seq.seq.len -= count;
+ iter->seq.seq.len = save_len;
+ break;
+ }
+
+ count = trace_seq_used(&iter->seq) - save_len;
+ if (rem < count) {
+ rem = 0;
+ iter->seq.seq.len = save_len;;
break;
}
@@ -4669,13 +4682,13 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
/* Copy the data into the page, so we can start over. */
ret = trace_seq_to_buffer(&iter->seq,
page_address(spd.pages[i]),
- iter->seq.seq.len);
+ trace_seq_used(&iter->seq));
if (ret < 0) {
__free_page(spd.pages[i]);
break;
}
spd.partial[i].offset = 0;
- spd.partial[i].len = iter->seq.seq.len;
+ spd.partial[i].len = trace_seq_used(&iter->seq);
trace_seq_init(&iter->seq);
}
@@ -5676,7 +5689,8 @@ tracing_stats_read(struct file *filp, char __user *ubuf,
cnt = ring_buffer_read_events_cpu(trace_buf->buffer, cpu);
trace_seq_printf(s, "read events: %ld\n", cnt);
- count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->seq.len);
+ count = simple_read_from_buffer(ubuf, count, ppos,
+ s->buffer, trace_seq_used(s));
kfree(s);
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 4d0067dd7f88..935cbea78532 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1044,7 +1044,8 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
mutex_unlock(&event_mutex);
if (file)
- r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
+ r = simple_read_from_buffer(ubuf, cnt, ppos,
+ s->buffer, trace_seq_used(s));
kfree(s);
@@ -1210,7 +1211,8 @@ subsystem_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
trace_seq_init(s);
print_subsystem_event_filter(system, s);
- r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
+ r = simple_read_from_buffer(ubuf, cnt, ppos,
+ s->buffer, trace_seq_used(s));
kfree(s);
@@ -1265,7 +1267,8 @@ show_header(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
trace_seq_init(s);
func(s);
- r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
+ r = simple_read_from_buffer(ubuf, cnt, ppos,
+ s->buffer, trace_seq_used(s));
kfree(s);
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 6d1342ae7a44..ec35468349a7 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -1153,6 +1153,9 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
return ret;
}
+ if (trace_seq_has_overflowed(s))
+ goto out;
+
/* Strip ending newline */
if (s->buffer[s->seq.len - 1] == '\n') {
s->buffer[s->seq.len - 1] = '\0';
@@ -1160,7 +1163,7 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
}
trace_seq_puts(s, " */\n");
-
+ out:
return trace_handle_return(s);
}
diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
index 087fa514069d..0c7aab4dd94f 100644
--- a/kernel/trace/trace_seq.c
+++ b/kernel/trace/trace_seq.c
@@ -30,7 +30,7 @@
#define TRACE_SEQ_BUF_LEFT(s) seq_buf_buffer_left(&(s)->seq)
/* How much buffer is written? */
-#define TRACE_SEQ_BUF_USED(s) min((s)->seq.len, (unsigned int)(PAGE_SIZE - 1))
+#define TRACE_SEQ_BUF_USED(s) seq_buf_used(&(s)->seq)
/*
* trace_seq should work with being initialized with 0s.
--
1.8.1.4
--
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