Messages in this thread | | | Subject | Re: [PATCH bpf] bpf: Fix kernel BUG in purge_effective_progs | From | Pu Lehui <> | Date | Thu, 18 Aug 2022 10:46:33 +0800 |
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On 2022/8/17 4:39, Andrii Nakryiko wrote: > On Sat, Aug 13, 2022 at 6:11 AM Pu Lehui <pulehui@huawei.com> wrote: >> >> Syzkaller reported kernel BUG as follows: >> >> ------------[ cut here ]------------ >> kernel BUG at kernel/bpf/cgroup.c:925! >> invalid opcode: 0000 [#1] PREEMPT SMP NOPTI >> CPU: 1 PID: 194 Comm: detach Not tainted 5.19.0-14184-g69dac8e431af #8 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS >> rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 >> RIP: 0010:__cgroup_bpf_detach+0x1f2/0x2a0 >> Code: 00 e8 92 60 30 00 84 c0 75 d8 4c 89 e0 31 f6 85 f6 74 19 42 f6 84 >> 28 48 05 00 00 02 75 0e 48 8b 80 c0 00 00 00 48 85 c0 75 e5 <0f> 0b 48 >> 8b 0c5 >> RSP: 0018:ffffc9000055bdb0 EFLAGS: 00000246 >> RAX: 0000000000000000 RBX: ffff888100ec0800 RCX: ffffc900000f1000 >> RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff888100ec4578 >> RBP: 0000000000000000 R08: ffff888100ec0800 R09: 0000000000000040 >> R10: 0000000000000000 R11: 0000000000000000 R12: ffff888100ec4000 >> R13: 000000000000000d R14: ffffc90000199000 R15: ffff888100effb00 >> FS: 00007f68213d2b80(0000) GS:ffff88813bc80000(0000) >> knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 000055f74a0e5850 CR3: 0000000102836000 CR4: 00000000000006e0 >> Call Trace: >> <TASK> >> cgroup_bpf_prog_detach+0xcc/0x100 >> __sys_bpf+0x2273/0x2a00 >> __x64_sys_bpf+0x17/0x20 >> do_syscall_64+0x3b/0x90 >> entry_SYSCALL_64_after_hwframe+0x63/0xcd >> RIP: 0033:0x7f68214dbcb9 >> Code: 08 44 89 e0 5b 41 5c c3 66 0f 1f 84 00 00 00 00 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 ff8 >> RSP: 002b:00007ffeb487db68 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 >> RAX: ffffffffffffffda RBX: 000000000000000b RCX: 00007f68214dbcb9 >> RDX: 0000000000000090 RSI: 00007ffeb487db70 RDI: 0000000000000009 >> RBP: 0000000000000003 R08: 0000000000000012 R09: 0000000b00000003 >> R10: 00007ffeb487db70 R11: 0000000000000246 R12: 00007ffeb487dc20 >> R13: 0000000000000004 R14: 0000000000000001 R15: 000055f74a1011b0 >> </TASK> >> Modules linked in: >> ---[ end trace 0000000000000000 ]--- >> >> Repetition steps: >> For the following cgroup tree, >> >> root >> | >> cg1 >> | >> cg2 >> >> 1. attach prog2 to cg2, and then attach prog1 to cg1, both bpf progs >> attach type is NONE or OVERRIDE. >> 2. write 1 to /proc/thread-self/fail-nth for failslab. >> 3. detach prog1 for cg1, and then kernel BUG occur. >> >> Failslab injection will cause kmalloc fail and fall back to >> purge_effective_progs. The problem is that cg2 have attached another prog, >> so when go through cg2 layer, iteration will add pos to 1, and subsequent >> operations will be skipped by the following condition, and cg will meet >> NULL in the end. >> >> `if (pos && !(cg->bpf.flags[atype] & BPF_F_ALLOW_MULTI))` >> >> The NULL cg means no link or prog match, this is as expected, and it's not >> a bug. So here just skip the no match situation. >> >> Fixes: 4c46091ee985 ("bpf: Fix KASAN use-after-free Read in compute_effective_progs") >> Signed-off-by: Pu Lehui <pulehui@huawei.com> >> --- >> kernel/bpf/cgroup.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c >> index 59b7eb60d5b4..4a400cd63731 100644 >> --- a/kernel/bpf/cgroup.c >> +++ b/kernel/bpf/cgroup.c >> @@ -921,8 +921,10 @@ static void purge_effective_progs(struct cgroup *cgrp, struct bpf_prog *prog, >> pos++; >> } >> } >> + >> + /* no link or prog match, skip the cgroup of this layer */ >> + continue; >> found: >> - BUG_ON(!cg); > > I don't think it's necessary to remove this BUG_ON(), but it also > feels unnecessary for purge_effective_progs, so I don't mind it. > > Acked-by: Andrii Nakryiko <andrii@kernel.org> >
Hi,
Will this patch be accepted? I think we should CC stable.
Thanks, Lehui
>> progs = rcu_dereference_protected( >> desc->bpf.effective[atype], >> lockdep_is_held(&cgroup_mutex)); >> -- >> 2.25.1 >> > . >
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