Cong Wang wrote:
> From: Cong Wang <cong.wang@xxxxxxxxxxxxx>
>
> Pretty much similar to commit 1336c662474e
> ("bpf: Clear per_cpu pointers during bpf_prog_realloc") we also need to
> clear these two percpu pointers in bpf_prog_clone_create(), otherwise
> would get a double free:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000000
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 0 P4D 0
> Oops: 0000 [#1] SMP PTI
> CPU: 13 PID: 8140 Comm: kworker/13:247 Kdump: loaded Tainted: G W OE
> 5.11.0-rc4.bm.1-amd64+ #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> test_bpf: #1 TXA
> Workqueue: events bpf_prog_free_deferred
> RIP: 0010:percpu_ref_get_many.constprop.97+0x42/0xf0
> Code: [...]
> RSP: 0018:ffffa6bce1f9bda0 EFLAGS: 00010002
> RAX: 0000000000000001 RBX: 0000000000000000 RCX: 00000000021dfc7b
> RDX: ffffffffae2eeb90 RSI: 867f92637e338da5 RDI: 0000000000000046
> RBP: ffffa6bce1f9bda8 R08: 0000000000000000 R09: 0000000000000001
> R10: 0000000000000046 R11: 0000000000000000 R12: 0000000000000280
> R13: 0000000000000000 R14: 0000000000000000 R15: ffff9b5f3ffdedc0
> FS: 0000000000000000(0000) GS:ffff9b5f2fb40000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 000000027c36c002 CR4: 00000000003706e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> refill_obj_stock+0x5e/0xd0
> free_percpu+0xee/0x550
> __bpf_prog_free+0x4d/0x60
> process_one_work+0x26a/0x590
> worker_thread+0x3c/0x390
> ? process_one_work+0x590/0x590
> kthread+0x130/0x150
> ? kthread_park+0x80/0x80
> ret_from_fork+0x1f/0x30
>
> This bug is 100% reproducible with test_kmod.sh.
>
> Reported-by: Jiang Wang <jiang.wang@xxxxxxxxxxxxx>
> Fixes: 700d4796ef59 ("bpf: Optimize program stats")
> Fixes: ca06f55b9002 ("bpf: Add per-program recursion prevention mechanism")
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
> ---
Acked-by: John Fastabend <john.fastabend@xxxxxxxxx>
