Messages in this thread | | | Date | Wed, 2 Nov 2022 10:59:44 +0800 | Subject | Re: [PATCH -next] bpf, test_run: fix alignment problem in bpf_prog_test_run_skb() | From | zhongbaisong <> |
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On 2022/11/2 0:45, Daniel Borkmann wrote: > [ +kfence folks ]
+ cc: Alexander Potapenko, Marco Elver, Dmitry Vyukov
Do you have any suggestions about this problem?
Thanks,
.
> > On 11/1/22 5:04 AM, Baisong Zhong wrote: >> Recently, we got a syzkaller problem because of aarch64 >> alignment fault if KFENCE enabled. >> >> When the size from user bpf program is an odd number, like >> 399, 407, etc, it will cause skb shard info's alignment access, >> as seen below: >> >> BUG: KFENCE: use-after-free read in __skb_clone+0x23c/0x2a0 >> net/core/skbuff.c:1032 >> >> Use-after-free read at 0xffff6254fffac077 (in kfence-#213): >> __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:26 [inline] >> arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline] >> arch_atomic_inc include/linux/atomic-arch-fallback.h:270 [inline] >> atomic_inc include/asm-generic/atomic-instrumented.h:241 [inline] >> __skb_clone+0x23c/0x2a0 net/core/skbuff.c:1032 >> skb_clone+0xf4/0x214 net/core/skbuff.c:1481 >> ____bpf_clone_redirect net/core/filter.c:2433 [inline] >> bpf_clone_redirect+0x78/0x1c0 net/core/filter.c:2420 >> bpf_prog_d3839dd9068ceb51+0x80/0x330 >> bpf_dispatcher_nop_func include/linux/bpf.h:728 [inline] >> bpf_test_run+0x3c0/0x6c0 net/bpf/test_run.c:53 >> bpf_prog_test_run_skb+0x638/0xa7c net/bpf/test_run.c:594 >> bpf_prog_test_run kernel/bpf/syscall.c:3148 [inline] >> __do_sys_bpf kernel/bpf/syscall.c:4441 [inline] >> __se_sys_bpf+0xad0/0x1634 kernel/bpf/syscall.c:4381 >> >> kfence-#213: 0xffff6254fffac000-0xffff6254fffac196, size=407, >> cache=kmalloc-512 >> >> allocated by task 15074 on cpu 0 at 1342.585390s: >> kmalloc include/linux/slab.h:568 [inline] >> kzalloc include/linux/slab.h:675 [inline] >> bpf_test_init.isra.0+0xac/0x290 net/bpf/test_run.c:191 >> bpf_prog_test_run_skb+0x11c/0xa7c net/bpf/test_run.c:512 >> bpf_prog_test_run kernel/bpf/syscall.c:3148 [inline] >> __do_sys_bpf kernel/bpf/syscall.c:4441 [inline] >> __se_sys_bpf+0xad0/0x1634 kernel/bpf/syscall.c:4381 >> __arm64_sys_bpf+0x50/0x60 kernel/bpf/syscall.c:4381 >> >> To fix the problem, we round up allocations with kmalloc_size_roundup() >> so that build_skb()'s use of kize() is always alignment and no special >> handling of the memory is needed by KFENCE. >> >> Fixes: 1cf1cae963c2 ("bpf: introduce BPF_PROG_TEST_RUN command") >> Signed-off-by: Baisong Zhong <zhongbaisong@huawei.com> >> --- >> net/bpf/test_run.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c >> index 13d578ce2a09..058b67108873 100644 >> --- a/net/bpf/test_run.c >> +++ b/net/bpf/test_run.c >> @@ -774,6 +774,7 @@ static void *bpf_test_init(const union bpf_attr >> *kattr, u32 user_size, >> if (user_size > size) >> return ERR_PTR(-EMSGSIZE); >> + size = kmalloc_size_roundup(size); >> data = kzalloc(size + headroom + tailroom, GFP_USER); > > The fact that you need to do this roundup on call sites feels broken, no? > Was there some discussion / consensus that now all k*alloc() call sites > would need to be fixed up? Couldn't this be done transparently in k*alloc() > when KFENCE is enabled? I presume there may be lots of other such occasions > in the kernel where similar issue triggers, fixing up all call-sites feels > like ton of churn compared to api-internal, generic fix. > >> if (!data) >> return ERR_PTR(-ENOMEM); >> > > Thanks, > Daniel >
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