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

[Leon Romanovsky]

On Tue, Nov 30, 2021 at 02:53:16PM -0800, Andrii Nakryiko wrote:
> 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?

kvmalloc should be fixed do not print WARN_ON() on attempts to provide
such allocations sizes.

We are in RDMA, and everyone who receives this size as an input from the
user, seeing this type of error.

Thanks

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