Writing to buffer_subbuf_size_kb calls ring_buffer_subbuf_order_set(),
which frees every sub-buffer of the ring buffer, including the reader
page, and replaces them with newly allocated ones.
Readers of trace_pipe hold pointers into those pages. ring_buffer_peek()
looks up an event under cpu_buffer->reader_lock but returns the event
pointer after dropping the lock, and peek_next_entry() then calls
ring_buffer_event_length() and ring_buffer_event_data() on it. If the
sub-buffer order is changed in that window, the reader dereferences
freed memory:
BUG: KASAN: use-after-free in ring_buffer_peek+0x3e0/0x430
Read of size 1 at addr ffff88802a4cf010 by task syz-executor989/6002
Freed by:
free_buffer_page kernel/trace/ring_buffer.c:398 [inline]
ring_buffer_subbuf_order_set+0x1325/0x18e0 kernel/trace/ring_buffer.c:7444
buffer_subbuf_size_write+0x182/0x280 kernel/trace/trace.c:8221
Take trace_access_lock(RING_BUFFER_ALL_CPUS) around the order change.
This is the lock trace_pipe readers already hold across their entire
peek-and-print loop, so the swap can no longer race with a reader that
is dereferencing a peeked event.
Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page")
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=685955db58555575fdd2
Tested-by: [email protected]
Signed-off-by: Deepanshu Kartikey <[email protected]>
---
kernel/trace/trace.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 395238b2b715..c38a5de602e0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8214,6 +8214,8 @@ buffer_subbuf_size_write(struct file *filp, const char
__user *ubuf,
/* Do not allow tracing while changing the order of the ring buffer */
tracing_stop_tr(tr);
+ trace_access_lock(RING_BUFFER_ALL_CPUS);
+
old_order = ring_buffer_subbuf_order_get(tr->array_buffer.buffer);
if (old_order == order)
goto out;
@@ -8253,6 +8255,7 @@ buffer_subbuf_size_write(struct file *filp, const char
__user *ubuf,
#endif
(*ppos)++;
out:
+ trace_access_unlock(RING_BUFFER_ALL_CPUS);
if (ret)
cnt = ret;
tracing_start_tr(tr);
--
2.43.0
