From: Josef Bacik josef@toxicpanda.com
commit c9a2f90f4d6b9d42b9912f7aaf68e8d748acfffd upstream.
There exists a race where we can be attempting to create a new nbd configuration while a previous configuration is going down, both configured with DESTROY_ON_DISCONNECT. Normally devices all have a reference of 1, as they won't be cleaned up until the module is torn down. However with DESTROY_ON_DISCONNECT we'll make sure that there is only 1 reference (generally) on the device for the config itself, and then once the config is dropped, the device is torn down.
The race that exists looks like this
TASK1 TASK2 nbd_genl_connect() idr_find() refcount_inc_not_zero(nbd) * count is 2 here ^^ nbd_config_put() nbd_put(nbd) (count is 1) setup new config check DESTROY_ON_DISCONNECT put_dev = true if (put_dev) nbd_put(nbd) * free'd here ^^
In nbd_genl_connect() we assume that the nbd ref count will be 2, however clearly that won't be true if the nbd device had been setup as DESTROY_ON_DISCONNECT with its prior configuration. Fix this by getting rid of the runtime flag to check if we need to mess with the nbd device refcount, and use the device NBD_DESTROY_ON_DISCONNECT flag to check if we need to adjust the ref counts. This was reported by syzkaller with the following kasan dump
BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:71 [inline] BUG: KASAN: use-after-free in atomic_read include/asm-generic/atomic-instrumented.h:27 [inline] BUG: KASAN: use-after-free in refcount_dec_not_one+0x71/0x1e0 lib/refcount.c:76 Read of size 4 at addr ffff888143bf71a0 by task systemd-udevd/8451
CPU: 0 PID: 8451 Comm: systemd-udevd Not tainted 5.11.0-rc7-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:79 [inline] dump_stack+0x107/0x163 lib/dump_stack.c:120 print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:230 __kasan_report mm/kasan/report.c:396 [inline] kasan_report.cold+0x79/0xd5 mm/kasan/report.c:413 check_memory_region_inline mm/kasan/generic.c:179 [inline] check_memory_region+0x13d/0x180 mm/kasan/generic.c:185 instrument_atomic_read include/linux/instrumented.h:71 [inline] atomic_read include/asm-generic/atomic-instrumented.h:27 [inline] refcount_dec_not_one+0x71/0x1e0 lib/refcount.c:76 refcount_dec_and_mutex_lock+0x19/0x140 lib/refcount.c:115 nbd_put drivers/block/nbd.c:248 [inline] nbd_release+0x116/0x190 drivers/block/nbd.c:1508 __blkdev_put+0x548/0x800 fs/block_dev.c:1579 blkdev_put+0x92/0x570 fs/block_dev.c:1632 blkdev_close+0x8c/0xb0 fs/block_dev.c:1640 __fput+0x283/0x920 fs/file_table.c:280 task_work_run+0xdd/0x190 kernel/task_work.c:140 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop kernel/entry/common.c:174 [inline] exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:201 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline] syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7fc1e92b5270 Code: 73 01 c3 48 8b 0d 38 7d 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 59 c1 20 00 00 75 10 b8 03 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 ee fb ff ff 48 89 04 24 RSP: 002b:00007ffe8beb2d18 EFLAGS: 00000246 ORIG_RAX: 0000000000000003 RAX: 0000000000000000 RBX: 0000000000000007 RCX: 00007fc1e92b5270 RDX: 000000000aba9500 RSI: 0000000000000000 RDI: 0000000000000007 RBP: 00007fc1ea16f710 R08: 000000000000004a R09: 0000000000000008 R10: 0000562f8cb0b2a8 R11: 0000000000000246 R12: 0000000000000000 R13: 0000562f8cb0afd0 R14: 0000000000000003 R15: 000000000000000e
Allocated by task 1: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 kasan_set_track mm/kasan/common.c:46 [inline] set_alloc_info mm/kasan/common.c:401 [inline] ____kasan_kmalloc.constprop.0+0x82/0xa0 mm/kasan/common.c:429 kmalloc include/linux/slab.h:552 [inline] kzalloc include/linux/slab.h:682 [inline] nbd_dev_add+0x44/0x8e0 drivers/block/nbd.c:1673 nbd_init+0x250/0x271 drivers/block/nbd.c:2394 do_one_initcall+0x103/0x650 init/main.c:1223 do_initcall_level init/main.c:1296 [inline] do_initcalls init/main.c:1312 [inline] do_basic_setup init/main.c:1332 [inline] kernel_init_freeable+0x605/0x689 init/main.c:1533 kernel_init+0xd/0x1b8 init/main.c:1421 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Freed by task 8451: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 kasan_set_track+0x1c/0x30 mm/kasan/common.c:46 kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:356 ____kasan_slab_free+0xe1/0x110 mm/kasan/common.c:362 kasan_slab_free include/linux/kasan.h:192 [inline] slab_free_hook mm/slub.c:1547 [inline] slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1580 slab_free mm/slub.c:3143 [inline] kfree+0xdb/0x3b0 mm/slub.c:4139 nbd_dev_remove drivers/block/nbd.c:243 [inline] nbd_put.part.0+0x180/0x1d0 drivers/block/nbd.c:251 nbd_put drivers/block/nbd.c:295 [inline] nbd_config_put+0x6dd/0x8c0 drivers/block/nbd.c:1242 nbd_release+0x103/0x190 drivers/block/nbd.c:1507 __blkdev_put+0x548/0x800 fs/block_dev.c:1579 blkdev_put+0x92/0x570 fs/block_dev.c:1632 blkdev_close+0x8c/0xb0 fs/block_dev.c:1640 __fput+0x283/0x920 fs/file_table.c:280 task_work_run+0xdd/0x190 kernel/task_work.c:140 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop kernel/entry/common.c:174 [inline] exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:201 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline] syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x44/0xa9
The buggy address belongs to the object at ffff888143bf7000 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 416 bytes inside of 1024-byte region [ffff888143bf7000, ffff888143bf7400) The buggy address belongs to the page: page:000000005238f4ce refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x143bf0 head:000000005238f4ce order:3 compound_mapcount:0 compound_pincount:0 flags: 0x57ff00000010200(slab|head) raw: 057ff00000010200 ffffea00004b1400 0000000300000003 ffff888010c41140 raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: ffff888143bf7080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888143bf7100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888143bf7180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^ ffff888143bf7200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
Reported-and-tested-by: syzbot+429d3f82d757c211bff3@syzkaller.appspotmail.com Signed-off-by: Josef Bacik josef@toxicpanda.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/block/nbd.c | 32 +++++++++++++++++++------------- 1 file changed, 19 insertions(+), 13 deletions(-)
--- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -78,8 +78,7 @@ struct link_dead_args { #define NBD_RT_HAS_PID_FILE 3 #define NBD_RT_HAS_CONFIG_REF 4 #define NBD_RT_BOUND 5 -#define NBD_RT_DESTROY_ON_DISCONNECT 6 -#define NBD_RT_DISCONNECT_ON_CLOSE 7 +#define NBD_RT_DISCONNECT_ON_CLOSE 6
#define NBD_DESTROY_ON_DISCONNECT 0 #define NBD_DISCONNECT_REQUESTED 1 @@ -1924,12 +1923,21 @@ again: if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) { u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]); if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) { - set_bit(NBD_RT_DESTROY_ON_DISCONNECT, - &config->runtime_flags); - set_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags); - put_dev = true; + /* + * We have 1 ref to keep the device around, and then 1 + * ref for our current operation here, which will be + * inherited by the config. If we already have + * DESTROY_ON_DISCONNECT set then we know we don't have + * that extra ref already held so we don't need the + * put_dev. + */ + if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT, + &nbd->flags)) + put_dev = true; } else { - clear_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags); + if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT, + &nbd->flags)) + refcount_inc(&nbd->refs); } if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) { set_bit(NBD_RT_DISCONNECT_ON_CLOSE, @@ -2100,15 +2108,13 @@ static int nbd_genl_reconfigure(struct s if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) { u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]); if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) { - if (!test_and_set_bit(NBD_RT_DESTROY_ON_DISCONNECT, - &config->runtime_flags)) + if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT, + &nbd->flags)) put_dev = true; - set_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags); } else { - if (test_and_clear_bit(NBD_RT_DESTROY_ON_DISCONNECT, - &config->runtime_flags)) + if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT, + &nbd->flags)) refcount_inc(&nbd->refs); - clear_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags); }
if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {