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@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

6 files changed, 42 insertions, 17 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/seq_buf.c b/kernel/trace/seq_buf.c
index 9ec5305d9da7..ce17f65268ed 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);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 0aa75be843a0..9023446b2c2b 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);
 
         /*
@@ -4598,7 +4598,7 @@ tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
                         break;
                 }
 
-                count = iter->seq.seq.len - save_len;
+                count = trace_seq_used(&iter->seq) - save_len;
                 if (rem < count) {
                         rem = 0;
                         iter->seq.seq.len = save_len;
@@ -4682,13 +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);
         }
@@ -5689,7 +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 74cacc930c24..f8b45d8792f9 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.