[PATCH net] Bluetooth: validate setsockopt(RFCOMM_LM) user input

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syzbot reported rfcomm_sock_setsockopt_old() 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 rfcomm_sock_setsockopt_old net/bluetooth/rfcomm/sock.c:632 [inline]
 BUG: KASAN: slab-out-of-bounds in rfcomm_sock_setsockopt+0x893/0xa70 net/bluetooth/rfcomm/sock.c:673
Read of size 4 at addr ffff8880209a8bc3 by task syz-executor632/5064

CPU: 0 PID: 5064 Comm: syz-executor632 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:
  __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]
  rfcomm_sock_setsockopt_old net/bluetooth/rfcomm/sock.c:632 [inline]
  rfcomm_sock_setsockopt+0x893/0xa70 net/bluetooth/rfcomm/sock.c:673
  do_sock_setsockopt+0x3af/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
RIP: 0033:0x7f36ff898dc9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 91 18 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe010c2208 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f36ff898dc9
RDX: 0000000000000003 RSI: 0000000000000012 RDI: 0000000000000006
RBP: 0000000000000006 R08: 0000000000000002 R09: 0000000000000000
R10: 00000000200000c0 R11: 0000000000000246 R12: 0000555567399338
R13: 000000000000000e R14: 0000000000000000 R15: 0000000000000000

Allocated by task 5064:
  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

The buggy address belongs to the object at ffff8880209a8bc0
 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 [ffff8880209a8bc0, ffff8880209a8bc2)

The buggy address belongs to the physical page:
page:ffffea0000826a00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x209a8
flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000800 ffff888014c41280 ffffea000081fb80 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 1, tgid 1 (swapper/0), ts 9917548498, free_ts 0
  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+0x2e5/0x4a0 mm/slub.c:3979
  kmalloc_array include/linux/slab.h:665 [inline]
  kcalloc include/linux/slab.h:696 [inline]
  group_cpus_evenly+0x294/0x5f0 lib/group_cpus.c:365
  blk_mq_map_queues+0x4c/0x3e0 block/blk-mq-cpumap.c:23
  blk_mq_alloc_tag_set+0x7ac/0xf40 block/blk-mq.c:4521
  nbd_dev_add+0x367/0xc80 drivers/block/nbd.c:1831
  nbd_init+0x224/0x2e0 drivers/block/nbd.c:2593
  do_one_initcall+0x238/0x830 init/main.c:1241
  do_initcall_level+0x157/0x210 init/main.c:1303
  do_initcalls+0x3f/0x80 init/main.c:1319
  kernel_init_freeable+0x435/0x5d0 init/main.c:1550
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8880209a8a80: 06 fc fc fc 06 fc fc fc 06 fc fc fc 07 fc fc fc
 ffff8880209a8b00: fa fc fc fc 05 fc fc fc 05 fc fc fc 05 fc fc fc
>ffff8880209a8b80: fa fc fc fc fa fc fc fc 02 fc fc fc fa fc fc fc
 ffff8880209a8c00: 00 fc fc fc 00 fc fc fc 00 fc fc fc 05 fc fc fc
 ffff8880209a8c80: 05 fc fc fc 05 fc fc fc fa fc fc fc 00 fc fc fc

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Marcel Holtmann <marcel@xxxxxxxxxxxx>
Cc: Johan Hedberg <johan.hedberg@xxxxxxxxx>
Cc: Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx> (supporter:BLUETOOTH SUBSYSTEM)
Cc: linux-bluetooth@xxxxxxxxxxxxxxx
 net/bluetooth/rfcomm/sock.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
index b54e8a530f55a1ff9547a2a5546db34059ebd672..39155b41e9d781a4099bb7b7f29bb53d8fc63e9e 100644
--- a/net/bluetooth/rfcomm/sock.c
+++ b/net/bluetooth/rfcomm/sock.c
@@ -629,6 +629,10 @@ static int rfcomm_sock_setsockopt_old(struct socket *sock, int optname,
 	switch (optname) {
 	case RFCOMM_LM:
+		if (optlen < sizeof(u32)) {
+			err = -EINVAL;
+			break;
+		}
 		if (copy_from_sockptr(&opt, optval, sizeof(u32))) {
 			err = -EFAULT;

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