Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
Pre-existing issues: - [High] The patch prevents a use-after-free for `trace_pipe` readers but leaves standard `trace` (seq_file) readers and `tracing_splice_read_pipe()` vulnerable to the exact same use-after-free. - [High] Snapshot buffer allocation and freeing call `ring_buffer_subbuf_order_set()` without holding `trace_access_lock`, leaving snapshot readers vulnerable to the exact same Use-After-Free race. - [High] Ring buffer resizing (`buffer_size_kb`) frees active pages without taking `trace_access_lock`, leading to a use-after-free for `seq_file` iterators. -- --- Patch [1]: [PATCH] tracing: Fix use-after-free in trace_pipe read on sub-buffer order change --- commit 36ad4aeed5301b8016b09a675a4d6aac8686489f Author: Deepanshu Kartikey <[email protected]> tracing: Fix use-after-free in trace_pipe read on sub-buffer order change 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. This patch adds trace_access_lock protection to prevent a use-after-free when readers hold pointers into those pages. Closes: https://syzkaller.appspot.com/bug?extid=685955db58555575fdd2 > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 19b0d7a53c589..34328916245df 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c [ ... ] > @@ -8216,6 +8216,8 @@ 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); > + [Severity: High] This isn't a bug introduced by this patch, but does the same use-after-free still exist for seq_file readers and tracing_splice_read_pipe()? While trace_pipe readers are now protected here, s_start() and tracing_splice_read_pipe() appear to peek the first event before taking the access lock: kernel/trace/trace.c:tracing_splice_read_pipe() { if (!iter->ent && !trace_find_next_entry_inc(iter)) { ret = -EFAULT; goto out_err; } trace_event_read_lock(); trace_access_lock(iter->cpu_file); ... } If a concurrent write to buffer_subbuf_size_kb runs during this unprotected window, could iter->ent be left pointing to freed memory? [Severity: High] This is a pre-existing issue, but do snapshot buffers need similar protection? It looks like free_snapshot() and tracing_alloc_snapshot_instance() call ring_buffer_subbuf_order_set() without holding trace_access_lock: kernel/trace/trace_snapshot.c:free_snapshot() { ... ring_buffer_subbuf_order_set(tr->snapshot_buffer.buffer, 0); ring_buffer_resize(tr->snapshot_buffer.buffer, 1, RING_BUFFER_ALL_CPUS); ... } Since the snapshot seq_file reader drops trace_types_lock before iterating, could a concurrent read of the snapshot file and a write to the snapshot file trigger the same use-after-free by freeing the pages while readers are active? [Severity: High] This is also a pre-existing issue, but does ring buffer resizing leave seq_file iterators vulnerable to a similar race? When writing to buffer_size_kb, __tracing_resize_ring_buffer() is called without taking trace_access_lock: kernel/trace/trace.c:__tracing_resize_ring_buffer() { tracing_stop_tr(tr); ret = ring_buffer_resize(tr->array_buffer.buffer, size, cpu); ... } Since ring_buffer_resize() frees active pages directly, could this cause a use-after-free if a seq_file reader is concurrently holding an event pointer that points into one of the freed pages? > old_order = ring_buffer_subbuf_order_get(tr->array_buffer.buffer); > if (old_order == order) > goto out; [ ... ] -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
