Messages in this thread Patch in this message | | | Date | Thu, 2 Aug 2018 14:25:37 -0700 | From | Roman Gushchin <> | Subject | Re: KASAN: use-after-free Read in bpf_cgroup_storage_release |
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On Thu, Aug 02, 2018 at 09:23:00PM +0200, Daniel Borkmann wrote: > [ +Roman ] > > On 08/02/2018 07:59 PM, syzbot wrote: > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: fc2a3b5dd618 Merge branch 'bpf-cgroup-local-storage' > > git tree: bpf-next > > console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D17a6a1c8400000&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=kNpA8CkCvXgMPDNNfqgkqDlGShzYMrSvH1AWBdBslJo&e= > > kernel config: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D3bfcc1651962483&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=PYjD3Jqpwgzv3cBV64k8EAbXwdolWkrrrcanCfJU6KQ&e= > > dashboard link: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D25554ab865a12b51c66f&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=FQHY4B4Ok0SJh_C-lkToT7mX_Ehj3NSHe6Fe1UiL--Y&e= > > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > > syzkaller repro:https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.syz-3Fx-3D12c4b9b4400000&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=38j2eoBTEgFiU2FlYHK86YXiVNEjxV6n3ug4tlAZ3MQ&e= > > C reproducer: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.c-3Fx-3D13e9d6f0400000&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=R75neIjoG9ODJgTDAUAfWqORwwOVX0k_cz7NsKyF6qw&e= > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+25554ab865a12b51c66f@syzkaller.appspotmail.com > > > > ================================================================== > > BUG: KASAN: use-after-free in debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline] > > BUG: KASAN: use-after-free in do_raw_spin_lock+0x1c0/0x200 kernel/locking/spinlock_debug.c:112 > > Read of size 4 at addr ffff8801c4723644 by task syz-executor865/9746 > > > > CPU: 0 PID: 9746 Comm: syz-executor865 Not tainted 4.18.0-rc5+ #68 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > Call Trace: > > __dump_stack lib/dump_stack.c:77 [inline] > > dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113 > > print_address_description+0x6c/0x20b mm/kasan/report.c:256 > > kasan_report_error mm/kasan/report.c:354 [inline] > > kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412 > > __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432 > > debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline] > > do_raw_spin_lock+0x1c0/0x200 kernel/locking/spinlock_debug.c:112 > > __raw_spin_lock_bh include/linux/spinlock_api_smp.h:136 [inline] > > _raw_spin_lock_bh+0x39/0x40 kernel/locking/spinlock.c:168 > > spin_lock_bh include/linux/spinlock.h:315 [inline] > > bpf_cgroup_storage_release+0x2c/0x110 kernel/bpf/local_storage.c:276 > > free_used_maps+0x81/0x200 kernel/bpf/syscall.c:961 > > bpf_prog_load+0x17ba/0x1c90 kernel/bpf/syscall.c:1414 > > __do_sys_bpf kernel/bpf/syscall.c:2338 [inline] > > __se_sys_bpf kernel/bpf/syscall.c:2300 [inline] > > __x64_sys_bpf+0x36c/0x510 kernel/bpf/syscall.c:2300 > > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe
So, it looks like we drop the last refcount on local storage map from release_maps() and schedule bpf_map_free_deferred(), which runs prior to bpf_cgroup_storage_release() in free_used_maps().
If so, here is the fix:
diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c index cd0b115c2395..fc4e37f68f2a 100644 --- a/kernel/bpf/local_storage.c +++ b/kernel/bpf/local_storage.c @@ -277,6 +277,7 @@ void bpf_cgroup_storage_release(struct bpf_prog *prog, struct bpf_map *_map) if (map->prog == prog) { WARN_ON(prog->aux->cgroup_storage != _map); map->prog = NULL; + prog->aux->cgroup_storage = NULL; } spin_unlock_bh(&map->lock); } --
I'll post an updated version (v7) in few minutes.
Thanks to syzbot team for the report!
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