ring-buffer: Fix possible dereference of uninitialized pointer

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@vger.kernel.org
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://patch.msgid.link/20260213100130.2013839-1-d.dulov@aladdin.ru
Closes: https://lore.kernel.org/r/202406130130.JtTGRf7W-lkp@intel.com/
Fixes: 5f3b6e839f3c ("ring-buffer: Validate boot range memory events")
Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index d331034089552d081f86be4e79d7725fa95997a9..bdc8010d8f482cc3092f145262815e9fee565f55 100644 (file)
--- 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;
 
        /*