Re: [PATCH -next v2] bpf: Add oversize check before call kvmalloc()

Leon Romanovsky
2021-12-01T11:23:36Z

On Wed, Dec 01, 2021 at 09:33:22AM +0800, Bixuan Cui 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@syzkaller.appspotmail.com
> Signed-off-by: Bixuan Cui <cuibixuan@linux.alibaba.com>
> ---
> Changes in v2:
> * Change the err from -EINVAL to -E2BIG;
> * Change "goto err_put" to "goto free_key";

Please fix kvmalloc instead.
https://lore.kernel.org/all/YadOjJXMTjP85MQx@unreal

diff --git a/mm/util.c b/mm/util.c
index 741ba32a43ac..3749f4a16ab9 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -594,7 +594,7 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
return ret;

/* Don't even allow crazy sizes */
- if (WARN_ON_ONCE(size > INT_MAX))
+ if (size > INT_MAX)
return NULL;

return __vmalloc_node(size, 1, flags, node,

>
> kernel/bpf/syscall.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 1033ee8..30aabdd 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 = -E2BIG;
> + goto free_key;
> + }
>
> err = -ENOMEM;
> value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN);
> --
> 1.8.3.1
>