cve/published/2025/CVE-2025-21778.mbox

From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2025-21778: tracing: Do not allow mmap() of persistent ring buffer

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

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

tracing: Do not allow mmap() of persistent ring buffer

When trying to mmap a trace instance buffer that is attached to
reserve_mem, it would crash:

 BUG: unable to handle page fault for address: ffffe97bd00025c8
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 2862f3067 P4D 2862f3067 PUD 0
 Oops: Oops: 0000 [#1] PREEMPT_RT SMP PTI
 CPU: 4 UID: 0 PID: 981 Comm: mmap-rb Not tainted 6.14.0-rc2-test-00003-g7f1a5e3fbf9e-dirty #233
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
 RIP: 0010:validate_page_before_insert+0x5/0xb0
 Code: e2 01 89 d0 c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 <48> 8b 46 08 a8 01 75 67 66 90 48 89 f0 8b 50 34 85 d2 74 76 48 89
 RSP: 0018:ffffb148c2f3f968 EFLAGS: 00010246
 RAX: ffff9fa5d3322000 RBX: ffff9fa5ccff9c08 RCX: 00000000b879ed29
 RDX: ffffe97bd00025c0 RSI: ffffe97bd00025c0 RDI: ffff9fa5ccff9c08
 RBP: ffffb148c2f3f9f0 R08: 0000000000000004 R09: 0000000000000004
 R10: 0000000000000000 R11: 0000000000000200 R12: 0000000000000000
 R13: 00007f16a18d5000 R14: ffff9fa5c48db6a8 R15: 0000000000000000
 FS:  00007f16a1b54740(0000) GS:ffff9fa73df00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: ffffe97bd00025c8 CR3: 00000001048c6006 CR4: 0000000000172ef0
 Call Trace:
  <TASK>
  ? __die_body.cold+0x19/0x1f
  ? __die+0x2e/0x40
  ? page_fault_oops+0x157/0x2b0
  ? search_module_extables+0x53/0x80
  ? validate_page_before_insert+0x5/0xb0
  ? kernelmode_fixup_or_oops.isra.0+0x5f/0x70
  ? __bad_area_nosemaphore+0x16e/0x1b0
  ? bad_area_nosemaphore+0x16/0x20
  ? do_kern_addr_fault+0x77/0x90
  ? exc_page_fault+0x22b/0x230
  ? asm_exc_page_fault+0x2b/0x30
  ? validate_page_before_insert+0x5/0xb0
  ? vm_insert_pages+0x151/0x400
  __rb_map_vma+0x21f/0x3f0
  ring_buffer_map+0x21b/0x2f0
  tracing_buffers_mmap+0x70/0xd0
  __mmap_region+0x6f0/0xbd0
  mmap_region+0x7f/0x130
  do_mmap+0x475/0x610
  vm_mmap_pgoff+0xf2/0x1d0
  ksys_mmap_pgoff+0x166/0x200
  __x64_sys_mmap+0x37/0x50
  x64_sys_call+0x1670/0x1d70
  do_syscall_64+0xbb/0x1d0
  entry_SYSCALL_64_after_hwframe+0x77/0x7f

The reason was that the code that maps the ring buffer pages to user space
has:

	page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]);

And uses that in:

	vm_insert_pages(vma, vma->vm_start, pages, &nr_pages);

But virt_to_page() does not work with vmap()'d memory which is what the
persistent ring buffer has. It is rather trivial to allow this, but for
now just disable mmap() of instances that have their ring buffer from the
reserve_mem option.

If an mmap() is performed on a persistent buffer it will return -ENODEV
just like it would if the .mmap field wasn't defined in the
file_operations structure.

The Linux kernel CVE team has assigned CVE-2025-21778 to this issue.


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

	Issue introduced in 6.12 with commit 9b7bdf6f6ece6ea888cc7d2f02c00b403b66a119 and fixed in 6.12.16 with commit e8dff5f73912513fc9b52ab992d861517c9a9975
	Issue introduced in 6.12 with commit 9b7bdf6f6ece6ea888cc7d2f02c00b403b66a119 and fixed in 6.13.4 with commit cf5aa560e5c7628b57c928741d7e6a9a0f6f0e67
	Issue introduced in 6.12 with commit 9b7bdf6f6ece6ea888cc7d2f02c00b403b66a119 and fixed in 6.14 with commit 129fe718819cc5e24ea2f489db9ccd4371f0c6f6

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-2025-21778
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/e8dff5f73912513fc9b52ab992d861517c9a9975
	https://git.kernel.org/stable/c/cf5aa560e5c7628b57c928741d7e6a9a0f6f0e67
	https://git.kernel.org/stable/c/129fe718819cc5e24ea2f489db9ccd4371f0c6f6