linux-kernel - Re: [PATCH] ring-buffer: Fix a oob in __rb_map

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Message-ID: <tencent_4F9EBF1BA54B1A1B74257CBA08BB49334F08@qq.com>
Date: Wed, 18 Dec 2024 07:43:46 +0800
From: Edward Adam Davis <eadavis@...com>
To: rostedt@...dmis.org
Cc: eadavis@...com,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	mathieu.desnoyers@...icios.com,
	mhiramat@...nel.org,
	syzbot+345e4443a21200874b18@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] ring-buffer: Fix a oob in __rb_map_vma

On Tue, 17 Dec 2024 12:46:02 -0500, Steven Rostedt wrote:
> On Mon, 16 Dec 2024 22:07:57 +0800
> Edward Adam Davis <eadavis@...com> wrote:
> 
> > syzbot report a slab-out-of-bounds in __rb_map_vma. [1]
> > 
> > Overflow occurred when performing the following calculation:
> > nr_pages = ((nr_subbufs + 1) << subbuf_order) - pgoff;
> > 
> > Add a check before the calculation to avoid this problem.
> > 
> > [1]
> > BUG: KASAN: slab-out-of-bounds in __rb_map_vma+0x9ab/0xae0 kernel/trace/ring_buffer.c:7058
> > Read of size 8 at addr ffff8880767dd2b8 by task syz-executor187/5836
> > 
> > CPU: 0 UID: 0 PID: 5836 Comm: syz-executor187 Not tainted 6.13.0-rc2-syzkaller-00159-gf932fb9b4074 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/25/2024
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:94 [inline]
> >  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
> >  print_address_description mm/kasan/report.c:378 [inline]
> >  print_report+0xc3/0x620 mm/kasan/report.c:489
> >  kasan_report+0xd9/0x110 mm/kasan/report.c:602
> >  __rb_map_vma+0x9ab/0xae0 kernel/trace/ring_buffer.c:7058
> >  ring_buffer_map+0x56e/0x9b0 kernel/trace/ring_buffer.c:7138
> >  tracing_buffers_mmap+0xa6/0x120 kernel/trace/trace.c:8482
> >  call_mmap include/linux/fs.h:2183 [inline]
> >  mmap_file mm/internal.h:124 [inline]
> >  __mmap_new_file_vma mm/vma.c:2291 [inline]
> >  __mmap_new_vma mm/vma.c:2355 [inline]
> >  __mmap_region+0x1786/0x2670 mm/vma.c:2456
> >  mmap_region+0x127/0x320 mm/mmap.c:1348
> >  do_mmap+0xc00/0xfc0 mm/mmap.c:496
> >  vm_mmap_pgoff+0x1ba/0x360 mm/util.c:580
> >  ksys_mmap_pgoff+0x32c/0x5c0 mm/mmap.c:542
> >  __do_sys_mmap arch/x86/kernel/sys_x86_64.c:89 [inline]
> >  __se_sys_mmap arch/x86/kernel/sys_x86_64.c:82 [inline]
> >  __x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:82
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > 
> > Reported-by: syzbot+345e4443a21200874b18@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=345e4443a21200874b18
> > Tested-by: syzbot+345e4443a21200874b18@...kaller.appspotmail.com
> > Signed-off-by: Edward Adam Davis <eadavis@...com>
> > ---
> >  kernel/trace/ring_buffer.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> > index 7e257e855dd1..15c43d7415d5 100644
> > --- a/kernel/trace/ring_buffer.c
> > +++ b/kernel/trace/ring_buffer.c
> > @@ -7019,6 +7019,9 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
> >  	lockdep_assert_held(&cpu_buffer->mapping_lock);
> >  
> >  	nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */
> > +	if (((nr_subbufs + 1) << subbuf_order) < pgoff)
> > +		return -EINVAL;
> > +
> 
> A proper fix is being discussed here:
First, my fix is the first one.
Second, the root cause of the problem is an overflow when calculating nr_pages.
> 
> https://lore.kernel.org/linux-trace-kernel/20241216164931.57323-1-aha310510@gmail.com/
> 
> Thank you,
> 
> -- Steve
> 
The calculation of nr_pages below overflows because the pgoff value is 8,
the nr_subbufs value is 3, and the subbuf_order value is 0.
> >  	nr_pages = ((nr_subbufs + 1) << subbuf_order) - pgoff; /* + meta-page */
> >  
> >  	nr_vma_pages = vma_pages(vma);
BR,
Edward