Message-ID: <CABBYNZ+F44x3aYK1kKUi8vLJT04QF48ONzrW06YJz=aq_oSHzA@mail.gmail.com>
Date: Fri, 5 Apr 2024 12:24:34 -0400
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	syzbot <syzkaller@...glegroups.com>, Marcel Holtmann <marcel@...tmann.org>, 
	Johan Hedberg <johan.hedberg@...il.com>, linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH net] Bluetooth: validate setsockopt( BT_PKT_STATUS /
 BT_DEFER_SETUP) user input

Hi Eric,

On Fri, Apr 5, 2024 at 6:19 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Thu, Apr 4, 2024 at 11:07 PM Luiz Augusto von Dentz
> <luiz.dentz@...il.com> wrote:
> >
> > Hi Eric,
> >
> > On Thu, Apr 4, 2024 at 3:04 PM Eric Dumazet <edumazet@...gle.com> wrote:
> > >
> > > On Thu, Apr 4, 2024 at 8:31 PM Luiz Augusto von Dentz
> > > <luiz.dentz@...il.com> wrote:
> > > >
> > > > Hi Eric,
> > > >
> > > > On Thu, Apr 4, 2024 at 8:36 AM Eric Dumazet <edumazet@...gle.com> wrote:
> > > > >
> > > > > syzbot reported sco_sock_setsockopt() is copying data without
> > > > > checking user input length.
> > > > >
> > > > >  BUG: KASAN: slab-out-of-bounds in copy_from_sockptr_offset include/linux/sockptr.h:49 [inline]
> > > > >  BUG: KASAN: slab-out-of-bounds in copy_from_sockptr include/linux/sockptr.h:55 [inline]
> > > > >  BUG: KASAN: slab-out-of-bounds in sco_sock_setsockopt+0xc0b/0xf90 net/bluetooth/sco.c:893
> > > > > Read of size 4 at addr ffff88805f7b15a3 by task syz-executor.5/12578
> > > > >
> > > > > CPU: 1 PID: 12578 Comm: syz-executor.5 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e #0
> > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> > > > > Call Trace:
> > > > >  <TASK>
> > > > >   __dump_stack lib/dump_stack.c:88 [inline]
> > > > >   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
> > > > >   print_address_description mm/kasan/report.c:377 [inline]
> > > > >   print_report+0x169/0x550 mm/kasan/report.c:488
> > > > >   kasan_report+0x143/0x180 mm/kasan/report.c:601
> > > > >   copy_from_sockptr_offset include/linux/sockptr.h:49 [inline]
> > > > >   copy_from_sockptr include/linux/sockptr.h:55 [inline]
> > > > >   sco_sock_setsockopt+0xc0b/0xf90 net/bluetooth/sco.c:893
> > > > >   do_sock_setsockopt+0x3b1/0x720 net/socket.c:2311
> > > > >   __sys_setsockopt+0x1ae/0x250 net/socket.c:2334
> > > > >   __do_sys_setsockopt net/socket.c:2343 [inline]
> > > > >   __se_sys_setsockopt net/socket.c:2340 [inline]
> > > > >   __x64_sys_setsockopt+0xb5/0xd0 net/socket.c:2340
> > > > >  do_syscall_64+0xfd/0x240
> > > > >  entry_SYSCALL_64_after_hwframe+0x6d/0x75
> > > > > RIP: 0033:0x7f3c2487dde9
> > > > > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
> > > > > RSP: 002b:00007f3c256b40c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
> > > > > RAX: ffffffffffffffda RBX: 00007f3c249abf80 RCX: 00007f3c2487dde9
> > > > > RDX: 0000000000000010 RSI: 0000000000000112 RDI: 0000000000000008
> > > > > RBP: 00007f3c248ca47a R08: 0000000000000002 R09: 0000000000000000
> > > > > R10: 0000000020000080 R11: 0000000000000246 R12: 0000000000000000
> > > > > R13: 000000000000004d R14: 00007f3c249abf80 R15: 00007fff5dcf4978
> > > > >  </TASK>
> > > > >
> > > > > Allocated by task 12578:
> > > > >   kasan_save_stack mm/kasan/common.c:47 [inline]
> > > > >   kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
> > > > >   poison_kmalloc_redzone mm/kasan/common.c:370 [inline]
> > > > >   __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:387
> > > > >   kasan_kmalloc include/linux/kasan.h:211 [inline]
> > > > >   __do_kmalloc_node mm/slub.c:3966 [inline]
> > > > >   __kmalloc+0x233/0x4a0 mm/slub.c:3979
> > > > >   kmalloc include/linux/slab.h:632 [inline]
> > > > >   __cgroup_bpf_run_filter_setsockopt+0xd2f/0x1040 kernel/bpf/cgroup.c:1869
> > > > >   do_sock_setsockopt+0x6b4/0x720 net/socket.c:2293
> > > > >   __sys_setsockopt+0x1ae/0x250 net/socket.c:2334
> > > > >   __do_sys_setsockopt net/socket.c:2343 [inline]
> > > > >   __se_sys_setsockopt net/socket.c:2340 [inline]
> > > > >   __x64_sys_setsockopt+0xb5/0xd0 net/socket.c:2340
> > > > >  do_syscall_64+0xfd/0x240
> > > > >  entry_SYSCALL_64_after_hwframe+0x6d/0x75
> > > > >
> > > > > The buggy address belongs to the object at ffff88805f7b15a0
> > > > >  which belongs to the cache kmalloc-8 of size 8
> > > > > The buggy address is located 1 bytes to the right of
> > > > >  allocated 2-byte region [ffff88805f7b15a0, ffff88805f7b15a2)
> > > > >
> > > > > The buggy address belongs to the physical page:
> > > > > page:ffffea00017dec40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5f7b1
> > > > > flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
> > > > > page_type: 0xffffffff()
> > > > > raw: 00fff00000000800 ffff888014c41280 ffffea0000a26d80 dead000000000002
> > > > > raw: 0000000000000000 0000000080800080 00000001ffffffff 0000000000000000
> > > > > page dumped because: kasan: bad access detected
> > > > > page_owner tracks the page as allocated
> > > > > page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 5091, tgid 5091 (syz-executor.3), ts 75758857522, free_ts 75730585588
> > > > >   set_page_owner include/linux/page_owner.h:31 [inline]
> > > > >   post_alloc_hook+0x1ea/0x210 mm/page_alloc.c:1533
> > > > >   prep_new_page mm/page_alloc.c:1540 [inline]
> > > > >   get_page_from_freelist+0x33ea/0x3580 mm/page_alloc.c:3311
> > > > >   __alloc_pages+0x256/0x680 mm/page_alloc.c:4569
> > > > >   __alloc_pages_node include/linux/gfp.h:238 [inline]
> > > > >   alloc_pages_node include/linux/gfp.h:261 [inline]
> > > > >   alloc_slab_page+0x5f/0x160 mm/slub.c:2175
> > > > >   allocate_slab mm/slub.c:2338 [inline]
> > > > >   new_slab+0x84/0x2f0 mm/slub.c:2391
> > > > >   ___slab_alloc+0xc73/0x1260 mm/slub.c:3525
> > > > >   __slab_alloc mm/slub.c:3610 [inline]
> > > > >   __slab_alloc_node mm/slub.c:3663 [inline]
> > > > >   slab_alloc_node mm/slub.c:3835 [inline]
> > > > >   __do_kmalloc_node mm/slub.c:3965 [inline]
> > > > >   __kmalloc_node_track_caller+0x2d6/0x4e0 mm/slub.c:3986
> > > > >   kstrdup+0x3a/0x80 mm/util.c:62
> > > > >   __kernfs_new_node+0x9d/0x880 fs/kernfs/dir.c:611
> > > > >   kernfs_new_node+0x13a/0x240 fs/kernfs/dir.c:691
> > > > >   kernfs_create_dir_ns+0x43/0x120 fs/kernfs/dir.c:1052
> > > > >   sysfs_create_dir_ns+0x189/0x3a0 fs/sysfs/dir.c:59
> > > > >   create_dir lib/kobject.c:73 [inline]
> > > > >   kobject_add_internal+0x435/0x8d0 lib/kobject.c:240
> > > > >   kobject_add_varg lib/kobject.c:374 [inline]
> > > > >   kobject_init_and_add+0x124/0x190 lib/kobject.c:457
> > > > >   netdev_queue_add_kobject net/core/net-sysfs.c:1786 [inline]
> > > > >   netdev_queue_update_kobjects+0x1ee/0x5f0 net/core/net-sysfs.c:1838
> > > > >   register_queue_kobjects net/core/net-sysfs.c:1900 [inline]
> > > > >   netdev_register_kobject+0x265/0x320 net/core/net-sysfs.c:2140
> > > > > page last free pid 5103 tgid 5103 stack trace:
> > > > >   reset_page_owner include/linux/page_owner.h:24 [inline]
> > > > >   free_pages_prepare mm/page_alloc.c:1140 [inline]
> > > > >   free_unref_page_prepare+0x968/0xa90 mm/page_alloc.c:2346
> > > > >   free_unref_page_list+0x5a3/0x850 mm/page_alloc.c:2532
> > > > >   release_pages+0x2744/0x2a80 mm/swap.c:1042
> > > > >   tlb_batch_pages_flush mm/mmu_gather.c:98 [inline]
> > > > >   tlb_flush_mmu_free mm/mmu_gather.c:293 [inline]
> > > > >   tlb_flush_mmu+0x34d/0x4e0 mm/mmu_gather.c:300
> > > > >   tlb_finish_mmu+0xd4/0x200 mm/mmu_gather.c:392
> > > > >   exit_mmap+0x4b6/0xd40 mm/mmap.c:3300
> > > > >   __mmput+0x115/0x3c0 kernel/fork.c:1345
> > > > >   exit_mm+0x220/0x310 kernel/exit.c:569
> > > > >   do_exit+0x99e/0x27e0 kernel/exit.c:865
> > > > >   do_group_exit+0x207/0x2c0 kernel/exit.c:1027
> > > > >   __do_sys_exit_group kernel/exit.c:1038 [inline]
> > > > >   __se_sys_exit_group kernel/exit.c:1036 [inline]
> > > > >   __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1036
> > > > >  do_syscall_64+0xfd/0x240
> > > > >  entry_SYSCALL_64_after_hwframe+0x6d/0x75
> > > > >
> > > > > Memory state around the buggy address:
> > > > >  ffff88805f7b1480: 05 fc fc fc 05 fc fc fc fa fc fc fc 05 fc fc fc
> > > > >  ffff88805f7b1500: 05 fc fc fc 05 fc fc fc 05 fc fc fc 05 fc fc fc
> > > > > >ffff88805f7b1580: 04 fc fc fc 02 fc fc fc fa fc fc fc 05 fc fc fc
> > > > >                                ^
> > > > >  ffff88805f7b1600: fa fc fc fc 05 fc fc fc fa fc fc fc 05 fc fc fc
> > > > >  ffff88805f7b1680: 05 fc fc fc 05 fc fc fc 00 fc fc fc fa fc fc fc
> > > > >
> > > > > Fixes: 00398e1d5183 ("Bluetooth: Add support for BT_PKT_STATUS CMSG data for SCO connections")
> > > > > Fixes: b96e9c671b05 ("Bluetooth: Add BT_DEFER_SETUP option to sco socket")
> > > > > Reported-by: syzbot <syzkaller@...glegroups.com>
> > > > > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > > > > Cc: Marcel Holtmann <marcel@...tmann.org>
> > > > > Cc: Johan Hedberg <johan.hedberg@...il.com>
> > > > > Cc: Luiz Augusto von Dentz <luiz.dentz@...il.com> (supporter:BLUETOOTH SUBSYSTEM)
> > > > > Cc: linux-bluetooth@...r.kernel.org
> > > > > ---
> > > > >  net/bluetooth/sco.c | 8 ++++++++
> > > > >  1 file changed, 8 insertions(+)
> > > > >
> > > > > diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
> > > > > index 43daf965a01e4ac5c9329150080b00dcd63c7e1c..9d013f01865fd2509f28eac3bceadf682f0a5edb 100644
> > > > > --- a/net/bluetooth/sco.c
> > > > > +++ b/net/bluetooth/sco.c
> > > > > @@ -843,6 +843,10 @@ static int sco_sock_setsockopt(struct socket *sock, int level, int optname,
> > > > >                         break;
> > > > >                 }
> > > > >
> > > > > +               if (optlen < sizeof(u32)) {
> > > > > +                       err = -EINVAL;
> > > > > +                       break;
> > > > > +               }
> > > >
> > > > Usually we deal with this sort of problem by doing len =
> > > > min_t(unsigned int, sizeof(u32), optlen) so we truncate the value if
> > > > smaller, perhaps it would be better to have a helper function that
> > > > does len check internally.
> > >
> > > Well, what happens if user provided optlen == 1 ?
> > >
> > > opt would then contain 24 bits of garbage.
> >
> > We might need to do a memset so if userspace just send one byte that
> > would still work, not that are actually doing memset right now so you
> > are right that in that respect it is still broken since it accessing
> > uninitialized value which perhaps is not triggering any build errors
> > but I wonder if we should attempt to fix that as well.
>
> Historically, because of old BSD conventions, IPv4 do_ip_setsockopt()
> has accepted optlen == 1,
> but for instance IPv6 has been strict from day 1.
>
> do_ipv6_setsockopt() does not accept int options in a char
>
> Not sure why you want bluetooh to adopt lazy behavior, given that no
> application could possibly
> have used this so far (without risking a kernel bug)

Fair enough, if we don't really have any risk of breaking the API
(would result in using uninitialized memory) then I propose we do
something like this:

https://gist.github.com/Vudentz/c9092e8a3cb1e7e6a8fd384a51300eee

That said perhaps copy_from_sockptr shall really take into account
both source and destination lengths so it could incorporate the check
e.g. if (dst_size > src_size) but that might result in changing every
user of copy_from_sockptr thus I left it to be specific to bluetooth.

-- 
Luiz Augusto von Dentz

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