general protection fault in htab_elem_free_rcu

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: d31958b3 Add linux-next specific files for 20200710
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13935857100000
kernel config: https://syzkaller.appspot.com/x/.config?x=3fe4fccb94cbc1a6
dashboard link: https://syzkaller.appspot.com/bug?extid=a9db0ab6a8e0ca14351d
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=133db22b100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16fe6f1f100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a9db0a...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xf33bb70012bc003b: 0000 [#1] PREEMPT SMP KASAN
KASAN: maybe wild-memory-access in range [0x99ddd80095e001d8-0x99ddd80095e001df]
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.8.0-rc4-next-20200710-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:htab_elem_free kernel/bpf/hashtab.c:769 [inline]
RIP: 0010:htab_elem_free_rcu+0x4a/0x110 kernel/bpf/hashtab.c:779
Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 bc 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6b f8 48 8d 7d 18 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 82 00 00 00 44 8b 65 18 bf 05
RSP: 0018:ffffc90000007e48 EFLAGS: 00010a03
RAX: dffffc0000000000 RBX: ffff888084800010 RCX: 0000000000000001
RDX: 133bbb0012bc003b RSI: ffffffff8186891e RDI: 99ddd80095e001de
RBP: 99ddd80095e001c6 R08: 0000000000000000 R09: ffffffff8c5b09f7
R10: fffffbfff18b613e R11: 0000000000000000 R12: ffffc90000007ed8
R13: ffff888084800000 R14: 0000000000000000 R15: ffffffff89a86580
FS: 0000000000000000(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004c6368 CR3: 0000000009a79000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
rcu_do_batch kernel/rcu/tree.c:2418 [inline]
rcu_core+0x5dc/0x11d0 kernel/rcu/tree.c:2645
__do_softirq+0x34c/0xa60 kernel/softirq.c:292
asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:706
</IRQ>
__run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
do_softirq_own_stack+0x111/0x170 arch/x86/kernel/irq_64.c:77
invoke_softirq kernel/softirq.c:387 [inline]
__irq_exit_rcu kernel/softirq.c:417 [inline]
irq_exit_rcu+0x229/0x270 kernel/softirq.c:429
sysvec_apic_timer_interrupt+0x54/0x120 arch/x86/kernel/apic/apic.c:1090
asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:587
RIP: 0010:native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:61
Code: ff 4c 89 ef e8 93 66 c6 f9 e9 8e fe ff ff 48 89 df e8 86 66 c6 f9 eb 8a cc cc cc cc e9 07 00 00 00 0f 00 2d 34 9b 5b 00 fb f4 <c3> 90 e9 07 00 00 00 0f 00 2d 24 9b 5b 00 f4 c3 cc cc 55 53 e8 09
RSP: 0018:ffffffff89a07c70 EFLAGS: 00000293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffffffff89a86580 RSI: ffffffff87ed2968 RDI: ffffffff87ed293e
RBP: ffff8880a6a93064 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff8880a6a93064
R13: 1ffffffff1340f98 R14: ffff8880a6a93065 R15: 0000000000000001
arch_safe_halt arch/x86/include/asm/paravirt.h:150 [inline]
acpi_safe_halt+0x8d/0x110 drivers/acpi/processor_idle.c:111
acpi_idle_do_entry+0x15c/0x1b0 drivers/acpi/processor_idle.c:525
acpi_idle_enter+0x3f9/0xab0 drivers/acpi/processor_idle.c:651
cpuidle_enter_state+0xff/0x960 drivers/cpuidle/cpuidle.c:235
cpuidle_enter+0x4a/0xa0 drivers/cpuidle/cpuidle.c:346
call_cpuidle kernel/sched/idle.c:126 [inline]
cpuidle_idle_call kernel/sched/idle.c:214 [inline]
do_idle+0x431/0x6d0 kernel/sched/idle.c:276
cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:372
start_kernel+0x9cb/0xa06 init/main.c:1045
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243
Modules linked in:
---[ end trace 5ce7b44eaacf6c96 ]---
RIP: 0010:htab_elem_free kernel/bpf/hashtab.c:769 [inline]
RIP: 0010:htab_elem_free_rcu+0x4a/0x110 kernel/bpf/hashtab.c:779
Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 bc 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6b f8 48 8d 7d 18 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 82 00 00 00 44 8b 65 18 bf 05
RSP: 0018:ffffc90000007e48 EFLAGS: 00010a03
RAX: dffffc0000000000 RBX: ffff888084800010 RCX: 0000000000000001
RDX: 133bbb0012bc003b RSI: ffffffff8186891e RDI: 99ddd80095e001de
RBP: 99ddd80095e001c6 R08: 0000000000000000 R09: ffffffff8c5b09f7
R10: fffffbfff18b613e R11: 0000000000000000 R12: ffffc90000007ed8
R13: ffff888084800000 R14: 0000000000000000 R15: ffffffff89a86580
FS: 0000000000000000(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004c6368 CR3: 0000000009a79000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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[Hillf Danton]

Sat, 11 Jul 2020 10:03:19 -0700

Wait for elements on the rcu way home.

--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -98,6 +98,7 @@ struct bpf_htab {
u32 n_buckets; /* number of hash buckets */
u32 elem_size; /* size of each element in bytes */
u32 hashrnd;
+ struct wait_queue_head waitq;
};

/* each htab element is struct htab_elem + key + value */
@@ -500,6 +501,7 @@ static struct bpf_map *htab_map_alloc(un
goto free_prealloc;
}
}
+ init_waitqueue_head(&htab->waitq);

return &htab->map;

@@ -769,6 +771,8 @@ static void htab_elem_free(struct bpf_ht
if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH)
free_percpu(htab_elem_get_ptr(l, htab->map.key_size));
kfree(l);
+ if (atomic_dec_and_test(&htab->count))
+ wake_up(&htab->waitq);
}

static void htab_elem_free_rcu(struct rcu_head *head)
@@ -792,7 +796,6 @@ static void free_htab_elem(struct bpf_ht
if (htab_is_prealloc(htab)) {
__pcpu_freelist_push(&htab->freelist, &l->fnode);
} else {
- atomic_dec(&htab->count);
l->htab = htab;
call_rcu(&l->rcu, htab_elem_free_rcu);
}
@@ -1290,20 +1293,12 @@ static void htab_map_free(struct bpf_map
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);

- /* bpf_free_used_maps() or close(map_fd) will trigger this map_free callback.
- * bpf_free_used_maps() is called after bpf prog is no longer executing.
- * There is no need to synchronize_rcu() here to protect map elements.
- */
-
- /* some of free_htab_elem() callbacks for elements of this map may
- * not have executed. Wait for them.
- */
- rcu_barrier();
if (!htab_is_prealloc(htab))
delete_all_elements(htab);
else
prealloc_destroy(htab);

+ wait_event(htab->waitq, !atomic_read(&htab->count));
free_percpu(htab->extra_elems);
bpf_map_area_free(htab->buckets);
kfree(htab);

[syzbot]

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