On Tue, 17 Dec 2024 12:46:02 -0500, Steven Rostedt wrote:
> On Mon, 16 Dec 2024 22:07:57 +0800
> Edward Adam Davis <eada...@qq.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+345e4443a21200874...@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=345e4443a21200874b18
> > Tested-by: syzbot+345e4443a21200874...@syzkaller.appspotmail.com
> > Signed-off-by: Edward Adam Davis <eada...@qq.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-aha310...@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
