[syzbot] KASAN: use-after-free Read in drm_getunique

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5ff2756a Merge tag 'nfs-for-5.13-2' of git://git.linux-nfs..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11815dabd00000
kernel config: https://syzkaller.appspot.com/x/.config?x=770708ea7cfd4916
dashboard link: https://syzkaller.appspot.com/bug?extid=c3a706cec1ea99e1c693
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15b5b4b5d00000

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

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10638a6bd00000
final oops: https://syzkaller.appspot.com/x/report.txt?x=12638a6bd00000
console output: https://syzkaller.appspot.com/x/log.txt?x=14638a6bd00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c3a706...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in drm_getunique+0x23b/0x2a0 drivers/gpu/drm/drm_ioctl.c:124
Read of size 4 at addr ffff8880212cb818 by task syz-executor.0/8693

CPU: 1 PID: 8693 Comm: syz-executor.0 Not tainted 5.13.0-rc3-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+0x141/0x1d7 lib/dump_stack.c:120
print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:233
__kasan_report mm/kasan/report.c:419 [inline]
kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:436
drm_getunique+0x23b/0x2a0 drivers/gpu/drm/drm_ioctl.c:124
drm_ioctl_kernel+0x220/0x2e0 drivers/gpu/drm/drm_ioctl.c:787
drm_ioctl+0x4fd/0x9b0 drivers/gpu/drm/drm_ioctl.c:887
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:1069 [inline]
__se_sys_ioctl fs/ioctl.c:1055 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4665d9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc47c368188 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000056c038 RCX: 00000000004665d9
RDX: 0000000020000180 RSI: 00000000c0145401 RDI: 0000000000000003
RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056c038
R13: 00007fff26bf6f4f R14: 00007fc47c368300 R15: 0000000000022000

Allocated by task 8692:
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:428 [inline]
____kasan_kmalloc mm/kasan/common.c:507 [inline]
____kasan_kmalloc mm/kasan/common.c:466 [inline]
__kasan_kmalloc+0x9b/0xd0 mm/kasan/common.c:516
kmalloc include/linux/slab.h:556 [inline]
kzalloc include/linux/slab.h:686 [inline]
drm_master_create+0x40/0x4f0 drivers/gpu/drm/drm_auth.c:107
drm_new_set_master+0xd2/0x400 drivers/gpu/drm/drm_auth.c:143
drm_master_open+0x13e/0x1a0 drivers/gpu/drm/drm_auth.c:306
drm_open_helper drivers/gpu/drm/drm_file.c:355 [inline]
drm_open+0x6b4/0xb10 drivers/gpu/drm/drm_file.c:430
drm_stub_open+0x281/0x530 drivers/gpu/drm/drm_drv.c:1015
chrdev_open+0x266/0x770 fs/char_dev.c:414
do_dentry_open+0x4b9/0x11b0 fs/open.c:826
do_open fs/namei.c:3361 [inline]
path_openat+0x1c0e/0x27e0 fs/namei.c:3494
do_filp_open+0x190/0x3d0 fs/namei.c:3521
do_sys_openat2+0x16d/0x420 fs/open.c:1187
do_sys_open fs/open.c:1203 [inline]
__do_sys_openat fs/open.c:1219 [inline]
__se_sys_openat fs/open.c:1214 [inline]
__x64_sys_openat+0x13f/0x1f0 fs/open.c:1214
do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 8692:
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:357
____kasan_slab_free mm/kasan/common.c:360 [inline]
____kasan_slab_free mm/kasan/common.c:325 [inline]
__kasan_slab_free+0xfb/0x130 mm/kasan/common.c:368
kasan_slab_free include/linux/kasan.h:212 [inline]
slab_free_hook mm/slub.c:1582 [inline]
slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1607
slab_free mm/slub.c:3167 [inline]
kfree+0xe5/0x7f0 mm/slub.c:4217
kref_put include/linux/kref.h:65 [inline]
drm_master_put drivers/gpu/drm/drm_auth.c:399 [inline]
drm_new_set_master+0x314/0x400 drivers/gpu/drm/drm_auth.c:155
drm_setmaster_ioctl+0x3de/0x550 drivers/gpu/drm/drm_auth.c:240
drm_ioctl_kernel+0x220/0x2e0 drivers/gpu/drm/drm_ioctl.c:787
drm_ioctl+0x4fd/0x9b0 drivers/gpu/drm/drm_ioctl.c:887
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:1069 [inline]
__se_sys_ioctl fs/ioctl.c:1055 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff8880212cb800
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 24 bytes inside of
512-byte region [ffff8880212cb800, ffff8880212cba00)
The buggy address belongs to the page:
page:ffffea000084b200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x212c8
head:ffffea000084b200 order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888011041c80
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 8440, ts 58973220338, free_ts 58965641961
prep_new_page mm/page_alloc.c:2358 [inline]
get_page_from_freelist+0x1033/0x2b60 mm/page_alloc.c:3994
__alloc_pages+0x1b2/0x500 mm/page_alloc.c:5200
alloc_pages+0x18c/0x2a0 mm/mempolicy.c:2272
alloc_slab_page mm/slub.c:1645 [inline]
allocate_slab+0x2c5/0x4c0 mm/slub.c:1785
new_slab mm/slub.c:1848 [inline]
new_slab_objects mm/slub.c:2594 [inline]
___slab_alloc+0x4a1/0x810 mm/slub.c:2757
__slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2797
slab_alloc_node mm/slub.c:2879 [inline]
slab_alloc mm/slub.c:2921 [inline]
__kmalloc+0x315/0x330 mm/slub.c:4055
kmalloc include/linux/slab.h:561 [inline]
kzalloc include/linux/slab.h:686 [inline]
tomoyo_init_log+0x1376/0x1ee0 security/tomoyo/audit.c:275
tomoyo_supervisor+0x34d/0xf00 security/tomoyo/common.c:2097
tomoyo_audit_path_log security/tomoyo/file.c:168 [inline]
tomoyo_path_permission security/tomoyo/file.c:587 [inline]
tomoyo_path_permission+0x270/0x3a0 security/tomoyo/file.c:573
tomoyo_path_perm+0x2f0/0x400 security/tomoyo/file.c:838
security_inode_getattr+0xcf/0x140 security/security.c:1332
vfs_getattr fs/stat.c:139 [inline]
vfs_statx+0x164/0x390 fs/stat.c:207
vfs_fstatat fs/stat.c:225 [inline]
vfs_lstat include/linux/fs.h:3384 [inline]
__do_sys_newlstat+0x91/0x110 fs/stat.c:380
do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1298 [inline]
__free_pages_ok+0x476/0xce0 mm/page_alloc.c:1572
stack_depot_save+0x162/0x4e0 lib/stackdepot.c:336
kasan_save_stack+0x32/0x40 mm/kasan/common.c:40
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:428 [inline]
____kasan_kmalloc mm/kasan/common.c:507 [inline]
____kasan_kmalloc mm/kasan/common.c:466 [inline]
__kasan_kmalloc+0x9b/0xd0 mm/kasan/common.c:516
kmalloc include/linux/slab.h:556 [inline]
kzalloc include/linux/slab.h:686 [inline]
batadv_bla_get_backbone_gw+0xb8/0xb00 net/batman-adv/bridge_loop_avoidance.c:502
batadv_bla_update_own_backbone_gw net/batman-adv/bridge_loop_avoidance.c:565 [inline]
batadv_bla_tx+0x15d/0x24d0 net/batman-adv/bridge_loop_avoidance.c:2100
batadv_interface_tx+0x45b/0x1660 net/batman-adv/soft-interface.c:238
__netdev_start_xmit include/linux/netdevice.h:4944 [inline]
netdev_start_xmit include/linux/netdevice.h:4958 [inline]
xmit_one net/core/dev.c:3654 [inline]
dev_hard_start_xmit+0x1eb/0x920 net/core/dev.c:3670
__dev_queue_xmit+0x2133/0x3130 net/core/dev.c:4246
neigh_resolve_output net/core/neighbour.c:1495 [inline]
neigh_resolve_output+0x50e/0x820 net/core/neighbour.c:1475
neigh_output include/net/neighbour.h:510 [inline]
ip6_finish_output2+0x6ee/0x1700 net/ipv6/ip6_output.c:117
__ip6_finish_output net/ipv6/ip6_output.c:182 [inline]
__ip6_finish_output+0x4c1/0xe10 net/ipv6/ip6_output.c:161
ip6_finish_output+0x35/0x200 net/ipv6/ip6_output.c:192
NF_HOOK_COND include/linux/netfilter.h:290 [inline]
ip6_output+0x1e4/0x530 net/ipv6/ip6_output.c:215
dst_output include/net/dst.h:448 [inline]
NF_HOOK include/linux/netfilter.h:301 [inline]
ndisc_send_skb+0xa99/0x1750 net/ipv6/ndisc.c:508
ndisc_send_ns+0x3a9/0x840 net/ipv6/ndisc.c:650

Memory state around the buggy address:
ffff8880212cb700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880212cb780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880212cb800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880212cb880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880212cb900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
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

[Desmond Cheong]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Best,

Desmond 

[syzbot]

I see the command but can't find the corresponding bug.
Please resend the email to syzbo...@syzkaller.appspotmail.com address
that is the sender of the bug report (also present in the Reported-by tag).

> master
>
> Best,
> Desmond
>
> --
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[Desmond Cheong Zhi Xi]

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+c3a706...@syzkaller.appspotmail.com

Tested on:

commit: 614124be Linux 5.13-rc5
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=c15b5345da5524f6
dashboard link: https://syzkaller.appspot.com/bug?extid=c3a706cec1ea99e1c693
compiler: Debian clang version 11.0.1-2
patch: https://syzkaller.appspot.com/x/patch.diff?x=10496aa8300000

Note: testing is done by a robot and is best-effort only.

[Dan Carpenter]

Hi Desmond,

I have a Smatch check for these (sort of). There is a similar warning
in drm_master_release().

drivers/gpu/drm/drm_auth.c:320 drm_master_release() warn: unlocked access 'master' (line 318) expected lock '&dev->master_mutex'

drivers/gpu/drm/drm_auth.c
315 void drm_master_release(struct drm_file *file_priv)
316 {
317 struct drm_device *dev = file_priv->minor->dev;
318 struct drm_master *master = file_priv->master;
^^^^^^^^^^^^^^^^^^^^^^^^^^
We should probably do this assignment

319
320 mutex_lock(&dev->master_mutex);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
after we take this lock.

321 if (file_priv->magic)
322 idr_remove(&file_priv->master->magic_map, file_priv->magic);
323
324 if (!drm_is_current_master(file_priv))
325 goto out;
326
327 drm_legacy_lock_master_cleanup(dev, master);
328
329 if (dev->master == file_priv->master)
330 drm_drop_master(dev, file_priv);
331 out:
332 if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) {
333 /* Revoke any leases held by this or lessees, but only if
334 * this is the "real" master
335 */
336 drm_lease_revoke(master);
337 }
338
339 /* drop the master reference held by the file priv */
340 if (file_priv->master)
341 drm_master_put(&file_priv->master);
342 mutex_unlock(&dev->master_mutex);
343 }

regards,
dan carpenter

[Desmond Cheong Zhi Xi]

Hi Dan,

Thanks for the pointer! Looks like this could indeed produce a similar
use-after-free bug since 'master' should be protected by the lock, and
is dereferenced in subsequent function calls.

I can create a patch for this, including an explanation for how it might
become an error. May I include you in a Suggested-by: tag?

Best wishes,
Desmond

[Dan Carpenter]

I always sort of prefer Reported-by: tags to Suggested-by tags. Does
anyone count Suggested-by tags? :P

regards,
dan carpenter

[Desmond Cheong Zhi Xi]

Got it, will do!

Best wishes,
Desmond