tracing: Limit trace_marker writes to just 4K

Limit the max print event of trace_marker to just 4K string size. This must
also be less than the amount that can be held by a trace_seq along with
the text that is before the output (like the task name, PID, CPU, state,
etc). As trace_seq is made to handle large events (some greater than 4K).
Make the max size of a trace_marker write event be 4K which is guaranteed
to fit in the trace_seq buffer.

Link: https://lore.kernel.org/linux-trace-kernel/20240304223433.4ba47dff@gandalf.local.home
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8198bfc54b58d9729ab6f6318eb9720a32d40375..d16b95ca58a7a803188e25dc88605de58001f406 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7293,6 +7293,8 @@ tracing_free_buffer_release(struct inode *inode, struct file *filp)
        return 0;
 }
 
+#define TRACE_MARKER_MAX_SIZE          4096
+
 static ssize_t
 tracing_mark_write(struct file *filp, const char __user *ubuf,
                                        size_t cnt, loff_t *fpos)
@@ -7320,6 +7322,9 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
        if ((ssize_t)cnt < 0)
                return -EINVAL;
 
+       if (cnt > TRACE_MARKER_MAX_SIZE)
+               cnt = TRACE_MARKER_MAX_SIZE;
+
        meta_size = sizeof(*entry) + 2;  /* add '\0' and possible '\n' */
  again:
        size = cnt + meta_size;
@@ -7328,11 +7333,6 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
        if (cnt < FAULTED_SIZE)
                size += FAULTED_SIZE - cnt;
 
-       if (size > TRACE_SEQ_BUFFER_SIZE) {
-               cnt -= size - TRACE_SEQ_BUFFER_SIZE;
-               goto again;
-       }
-
        buffer = tr->array_buffer.buffer;
        event = __trace_buffer_lock_reserve(buffer, TRACE_PRINT, size,
                                            tracing_gen_ctx());