KASAN: use-after-free Read in nbd_release

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3af409ca net: enetc: fix destroyed phylink dereference dur..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=144bf26cd00000
kernel config: https://syzkaller.appspot.com/x/.config?x=8cb23303ddb9411f
dashboard link: https://syzkaller.appspot.com/bug?extid=74f888d2e102b3930324
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12917e5ad00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1131fb04d00000

Bisection is inconclusive: the issue happens on the oldest tested release.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1252220cd00000
final oops: https://syzkaller.appspot.com/x/report.txt?x=1152220cd00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1652220cd00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+74f888...@syzkaller.appspotmail.com

==================================================================
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
ffff888143bf7280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Hillf Danton]

Mon, 22 Feb 2021 01:05:20 -0800

In nbd_genl_connect() the code sequences related to refcnt look like

...

if (!refcount_inc_not_zero(&nbd->refs)) {
...

mutex_lock(&nbd->config_lock);

refcount_set(&nbd->config_refs, 1);

...
out:
mutex_unlock(&nbd->config_lock);
if (!ret) {
set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
refcount_inc(&nbd->config_refs);
nbd_connect_reply(info, nbd->index);
}
nbd_config_put(nbd);
if (put_dev)
nbd_put(nbd);
return ret;


and the balance of nbd->refs can be destroyed due to put_dev, as
nbd_config_put() has nbd_put() included.

The balance of nbd->config_refs can be destroyed in case of no
error because it makes no sense to put config.


--- x/drivers/block/nbd.c
+++ y/drivers/block/nbd.c
@@ -1794,7 +1794,6 @@ static int nbd_genl_connect(struct sk_bu
struct nbd_config *config;
int index = -1;
int ret;
- bool put_dev = false;

if (!netlink_capable(skb, CAP_SYS_ADMIN))
return -EPERM;
@@ -1907,7 +1906,6 @@ again:
set_bit(NBD_RT_DESTROY_ON_DISCONNECT,
&config->runtime_flags);
set_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags);
- put_dev = true;
} else {
clear_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags);
}
@@ -1954,10 +1952,8 @@ out:
set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
refcount_inc(&nbd->config_refs);
nbd_connect_reply(info, nbd->index);
- }
- nbd_config_put(nbd);
- if (put_dev)
- nbd_put(nbd);
+ } else
+ nbd_config_put(nbd);
return ret;
}

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.