From 307ed139d7af56502698438f0a737e4c7dfcac82 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Google)" Date: Tue, 12 Dec 2023 07:25:58 -0500 Subject: [PATCH] ring-buffer: Have saved event hold the entire event commit b049525855fdd0024881c9b14b8fbec61c3f53d3 upstream. For the ring buffer iterator (non-consuming read), the event needs to be copied into the iterator buffer to make sure that a writer does not overwrite it while the user is reading it. If a write happens during the copy, the buffer is simply discarded. But the temp buffer itself was not big enough. The allocation of the buffer was only BUF_MAX_DATA_SIZE, which is the maximum data size that can be passed into the ring buffer and saved. But the temp buffer needs to hold the meta data as well. That would be BUF_PAGE_SIZE and not BUF_MAX_DATA_SIZE. Link: https://lore.kernel.org/linux-trace-kernel/20231212072558.61f76493@gandalf.local.home Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Fixes: 785888c544e04 ("ring-buffer: Have rb_iter_head_event() handle concurrent writer") Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ring_buffer.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index c915a855..5de1e59 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2409,7 +2409,7 @@ rb_iter_head_event(struct ring_buffer_iter *iter) */ barrier(); - if ((iter->head + length) > commit || length > BUF_MAX_DATA_SIZE) + if ((iter->head + length) > commit || length > BUF_PAGE_SIZE) /* Writer corrupted the read? */ goto reset; @@ -5113,7 +5113,8 @@ ring_buffer_read_prepare(struct trace_buffer *buffer, int cpu, gfp_t flags) if (!iter) return NULL; - iter->event = kmalloc(BUF_MAX_DATA_SIZE, flags); + /* Holds the entire event: data and meta data */ + iter->event = kmalloc(BUF_PAGE_SIZE, flags); if (!iter->event) { kfree(iter); return NULL; -- 2.7.4