CVE-2026-89747: tracing: Fix use-after-free in trace_pipe read on sub-buffer order change

CVE-2026-89747: tracing: Fix use-after-free in trace_pipe read on sub-buffer order change

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

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.

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.

The Linux kernel CVE team has assigned CVE-2026-89747 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.8 with commit f9b94daa542a8d2532f0930f01cd9aec2d19621b and fixed in 6.12.109 with commit 05ebe1e1d7d38c2612bacfefe043a33572ae34cb
	Issue introduced in 6.8 with commit f9b94daa542a8d2532f0930f01cd9aec2d19621b and fixed in 6.18.50 with commit ddbe921ed16a0ad2d9e09574c3f3aabec7528325
	Issue introduced in 6.8 with commit f9b94daa542a8d2532f0930f01cd9aec2d19621b and fixed in 7.2.4 with commit 7a49d19ff9baaf61217e5ec14199c18bc2d93ee4
	Issue introduced in 6.8 with commit f9b94daa542a8d2532f0930f01cd9aec2d19621b and fixed in 7.3-rc1 with commit 372f8534244d632ad5118e8a87a11291b01712d3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89747
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/trace/trace.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/05ebe1e1d7d38c2612bacfefe043a33572ae34cb
	https://git.kernel.org/stable/c/ddbe921ed16a0ad2d9e09574c3f3aabec7528325
	https://git.kernel.org/stable/c/7a49d19ff9baaf61217e5ec14199c18bc2d93ee4
	https://git.kernel.org/stable/c/372f8534244d632ad5118e8a87a11291b01712d3