From 5dbeb56bb9589e1051f6af6877cd375f3a901afb Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Thu, 13 Mar 2025 07:16:18 -0400 Subject: [PATCH] tracing: Initialize scratch_size to zero to prevent UB In allocate_trace_buffer() the following code: buf->buffer = ring_buffer_alloc_range(size, rb_flags, 0, tr->range_addr_start, tr->range_addr_size, struct_size(tscratch, entries, 128)); tscratch = ring_buffer_meta_scratch(buf->buffer, &scratch_size); setup_trace_scratch(tr, tscratch, scratch_size); Has undefined behavior if ring_buffer_alloc_range() fails because "scratch_size" is not initialize. If the allocation fails, then buf->buffer will be NULL. The ring_buffer_meta_scratch() will return NULL immediately if it is passed a NULL buffer and it will not update scratch_size. Then setup_trace_scratch() will return immediately if tscratch is NULL. Although there's no real issue here, but it is considered undefined behavior to pass an uninitialized variable to a function as input, and UBSan may complain about it. Just initialize scratch_size to zero to make the code defined behavior and a little more robust. Link: https://lore.kernel.org/all/44c5deaa-b094-4852-90f9-52f3fb10e67a@stanley.mountain/ Reported-by: Dan Carpenter Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 7f8b0c43d2a5..78ae76666695 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -9398,7 +9398,7 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size { enum ring_buffer_flags rb_flags; struct trace_scratch *tscratch; - unsigned int scratch_size; + unsigned int scratch_size = 0; rb_flags = tr->trace_flags & TRACE_ITER_OVERWRITE ? RB_FL_OVERWRITE : 0;