[for-linus][PATCH 1/5] ring-buffer: Fix possible dereference of uninitialized pointer

[Steven Rostedt]

From: Daniil Dulov <d.dulov@xxxxxxxxxx>

There is a pointer head_page in rb_meta_validate_events() which is not
initialized at the beginning of a function. This pointer can be dereferenced
if there is a failure during reader page validation. In this case the control
is passed to "invalid" label where the pointer is dereferenced in a loop.

To fix the issue initialize orig_head and head_page before calling
rb_validate_buffer.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Link: https://patch.msgid.link/20260213100130.2013839-1-d.dulov@xxxxxxxxxx
Closes: https://lore.kernel.org/r/202406130130.JtTGRf7W-lkp@xxxxxxxxx/
Fixes: 5f3b6e839f3c ("ring-buffer: Validate boot range memory events")
Signed-off-by: Daniil Dulov <d.dulov@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/ring_buffer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index d33103408955..bdc8010d8f48 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1919,6 +1919,8 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	if (!meta || !meta->head_buffer)
 		return;
 
+	orig_head = head_page = cpu_buffer->head_page;
+
 	/* Do the reader page first */
 	ret = rb_validate_buffer(cpu_buffer->reader_page->page, cpu_buffer->cpu);
 	if (ret < 0) {
@@ -1929,7 +1931,6 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	entry_bytes += local_read(&cpu_buffer->reader_page->page->commit);
 	local_set(&cpu_buffer->reader_page->entries, ret);
 
-	orig_head = head_page = cpu_buffer->head_page;
 	ts = head_page->page->time_stamp;
 
 	/*
-- 
2.51.0