Re: [PATCH -next] bpf: Add oversize check before call kvmalloc()

[Andrii Nakryiko]

On Sat, Nov 27, 2021 at 7:32 AM Bixuan Cui <cuibixuan@xxxxxxxxxxxxxxxxx> wrote:
>
> Commit 7661809d493b ("mm: don't allow oversized kvmalloc() calls") add
> the oversize check. When the allocation is larger than what kvmalloc()
> supports, the following warning triggered:
>
> WARNING: CPU: 1 PID: 372 at mm/util.c:597 kvmalloc_node+0x111/0x120
> mm/util.c:597
> Modules linked in:
> CPU: 1 PID: 372 Comm: syz-executor.4 Not tainted 5.15.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:kvmalloc_node+0x111/0x120 mm/util.c:597
> Code: 01 00 00 00 4c 89 e7 e8 7d f7 0c 00 49 89 c5 e9 69 ff ff ff e8 60
> 20 d1 ff 41 89 ed 41 81 cd 00 20 01 00 eb 95 e8 4f 20 d1 ff <0f> 0b e9
> 4c ff ff ff 0f 1f 84 00 00 00 00 00 55 48 89 fd 53 e8 36
> RSP: 0018:ffffc90002bf7c98 EFLAGS: 00010216
> RAX: 00000000000000ec RBX: 1ffff9200057ef9f RCX: ffffc9000ac63000
> RDX: 0000000000040000 RSI: ffffffff81a6a621 RDI: 0000000000000003
> RBP: 0000000000102cc0 R08: 000000007fffffff R09: 00000000ffffffff
> R10: ffffffff81a6a5de R11: 0000000000000000 R12: 00000000ffff9aaa
> R13: 0000000000000000 R14: 00000000ffffffff R15: 0000000000000000
> FS:  00007f05f2573700(0000) GS:ffff8880b9d00000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b2f424000 CR3: 0000000027d2c000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  kvmalloc include/linux/slab.h:741 [inline]
>  map_lookup_elem kernel/bpf/syscall.c:1090 [inline]
>  __sys_bpf+0x3a5b/0x5f00 kernel/bpf/syscall.c:4603
>  __do_sys_bpf kernel/bpf/syscall.c:4722 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:4720 [inline]
>  __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:4720
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The type of 'value_size' is u32, its value may exceed INT_MAX.
>
> Reported-by: syzbot+cecf5b7071a0dfb76530@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Bixuan Cui <cuibixuan@xxxxxxxxxxxxxxxxx>
> ---
>  kernel/bpf/syscall.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 1033ee8..f5bc380 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -1094,6 +1094,10 @@ static int map_lookup_elem(union bpf_attr *attr)
>         }
>
>         value_size = bpf_map_value_size(map);
> +       if (value_size > INT_MAX) {
> +               err = -EINVAL;

-E2BIG makes a bit more sense in this scenario?

> +               goto err_put;
> +       }
>
>         err = -ENOMEM;
>         value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN);
> --
> 1.8.3.1
>