From: Masami Hiramatsu (Google) <[email protected]>
When ring_buffer_subbuf_order_set() updates buffer->subbuf_order, it
previously modified buffer->subbuf_order before clearing the cached
per-CPU free_page entries. Furthermore, clearing cpu_buffer->free_page
was done under cpu_buffer->reader_lock, whereas
ring_buffer_alloc_read_page() protects cpu_buffer->free_page using
arch_spin_lock(&cpu_buffer->lock).
Because ring_buffer_alloc_read_page(), ring_buffer_free_read_page(),
and ring_buffer_read_page() checked buffer->subbuf_order locklessly
before accessing reader resources, a TOCTOU race allowed a concurrent
reader to obtain, cache, or swap a page allocated under an outdated order
while tagging bpage->order with the new order. This allowed undersized
pages to be swapped into the ring buffer, leading to heap buffer overflows,
or caused free_pages() to be called with an invalid order.
Fix this by:
1. Flushing and freeing all per-CPU cached free_page entries under
arch_spin_lock(&cpu_buffer->lock) using old_order before modifying
buffer->subbuf_order.
2. Protecting bpage->order assignment under
arch_spin_lock(&cpu_buffer->lock) in ring_buffer_alloc_read_page().
3. Moving the buffer->subbuf_order validation inside
arch_spin_lock(&cpu_buffer->lock) in ring_buffer_free_read_page().
4. Re-validating buffer->subbuf_order inside reader_lock in
ring_buffer_read_page().
5. Protecting cpu_buffer->free_page extraction with
arch_spin_lock(&cpu_buffer->lock) in ring_buffer_subbuf_order_set().
Fixes: 2808e31ec12e ("ring-buffer: Add interface for configuring trace sub
buffer size")
Assisted-by: Antigravity:gemini-3.6-flash
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
---
kernel/trace/ring_buffer.c | 35 +++++++++++++++++++++++++++++------
1 file changed, 29 insertions(+), 6 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2667992f0aa2..6d180689ad59 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -6957,11 +6957,11 @@ ring_buffer_alloc_read_page(struct trace_buffer
*buffer, int cpu)
if (!bpage)
return ERR_PTR(-ENOMEM);
- bpage->order = buffer->subbuf_order;
cpu_buffer = buffer->buffers[cpu];
local_irq_save(flags);
arch_spin_lock(&cpu_buffer->lock);
+ bpage->order = buffer->subbuf_order;
if (cpu_buffer->free_page) {
bpage->data = cpu_buffer->free_page;
cpu_buffer->free_page = NULL;
@@ -7010,13 +7010,13 @@ void ring_buffer_free_read_page(struct trace_buffer
*buffer, int cpu,
* is different from the subbuffer order of the buffer -
* we can't reuse it
*/
- if (page_ref_count(page) > 1 || data_page->order !=
buffer->subbuf_order)
+ if (page_ref_count(page) > 1)
goto out;
local_irq_save(flags);
arch_spin_lock(&cpu_buffer->lock);
- if (!cpu_buffer->free_page) {
+ if (data_page->order == buffer->subbuf_order && !cpu_buffer->free_page)
{
cpu_buffer->free_page = dpage;
dpage = NULL;
}
@@ -7094,15 +7094,15 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
if (!data_page || !data_page->data)
return -1;
- if (data_page->order != buffer->subbuf_order)
- return -1;
-
dpage = data_page->data;
if (!dpage)
return -1;
guard(raw_spinlock_irqsave)(&cpu_buffer->reader_lock);
+ if (data_page->order != buffer->subbuf_order)
+ return -1;
+
reader = rb_get_reader_page(cpu_buffer);
if (!reader)
return -1;
@@ -7350,6 +7350,27 @@ int ring_buffer_subbuf_order_set(struct trace_buffer
*buffer, int order)
/* Make sure all commits have finished */
synchronize_rcu();
+ /* Flush any cached free_page allocated with old_order */
+ for_each_buffer_cpu(buffer, cpu) {
+ struct buffer_data_page *old_free;
+ unsigned long flags;
+
+ if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ continue;
+
+ cpu_buffer = buffer->buffers[cpu];
+
+ local_irq_save(flags);
+ arch_spin_lock(&cpu_buffer->lock);
+ old_free = cpu_buffer->free_page;
+ cpu_buffer->free_page = NULL;
+ arch_spin_unlock(&cpu_buffer->lock);
+ local_irq_restore(flags);
+
+ if (old_free)
+ free_pages((unsigned long)old_free, old_order);
+ }
+
buffer->subbuf_order = order;
buffer->subbuf_size = psize - BUF_PAGE_HDR_SIZE;
@@ -7431,8 +7452,10 @@ int ring_buffer_subbuf_order_set(struct trace_buffer
*buffer, int order)
cpu_buffer->nr_pages = cpu_buffer->nr_pages_to_update;
cpu_buffer->nr_pages_to_update = 0;
+ arch_spin_lock(&cpu_buffer->lock);
old_free_data_page = cpu_buffer->free_page;
cpu_buffer->free_page = NULL;
+ arch_spin_unlock(&cpu_buffer->lock);
rb_head_page_activate(cpu_buffer);
