linux-kernel - Re: [syzbot] WARNING: kmalloc bug in xdp_umem

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Message-ID: <20220210081125.GA4616@1wt.eu>
Date:   Thu, 10 Feb 2022 09:11:26 +0100
From:   Willy Tarreau <w@....eu>
To:     syzbot <syzbot+11421fbbff99b989670e@...kaller.appspotmail.com>
Cc:     akpm@...ux-foundation.org, andrii@...nel.org, ast@...nel.org,
        bjorn.topel@...il.com, bjorn.topel@...el.com, bjorn@...nel.org,
        bpf@...r.kernel.org, daniel@...earbox.net, davem@...emloft.net,
        fgheet255t@...il.com, hawk@...nel.org, john.fastabend@...il.com,
        jonathan.lemon@...il.com, kafai@...com, kpsingh@...nel.org,
        kuba@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        magnus.karlsson@...el.com, mudongliangabcd@...il.com,
        netdev@...r.kernel.org, songliubraving@...com,
        syzkaller-bugs@...glegroups.com, torvalds@...ux-foundation.org,
        yhs@...com
Subject: Re: [syzbot] WARNING: kmalloc bug in xdp_umem_create (2)

On Wed, Feb 09, 2022 at 10:08:07PM -0800, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit 7661809d493b426e979f39ab512e3adf41fbcc69
> Author: Linus Torvalds <torvalds@...ux-foundation.org>
> Date:   Wed Jul 14 16:45:49 2021 +0000
> 
>     mm: don't allow oversized kvmalloc() calls
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=13bc74c2700000
> start commit:   f4bc5bbb5fef Merge tag 'nfsd-5.17-2' of git://git.kernel.o..
> git tree:       upstream
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=107c74c2700000
> console output: https://syzkaller.appspot.com/x/log.txt?x=17bc74c2700000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5707221760c00a20
> dashboard link: https://syzkaller.appspot.com/bug?extid=11421fbbff99b989670e
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12e514a4700000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15fcdf8a700000
> 
> Reported-by: syzbot+11421fbbff99b989670e@...kaller.appspotmail.com
> Fixes: 7661809d493b ("mm: don't allow oversized kvmalloc() calls")
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Interesting, so in fact syzkaller has shown that the aforementioned
patch does its job well and has spotted a call path by which a single
userland setsockopt() can request more than 2 GB allocation in the
kernel. Most likely that's in fact what needs to be addressed.

FWIW the call trace at the URL above is:

Call Trace:
 kvmalloc include/linux/mm.h:806 [inline]
 kvmalloc_array include/linux/mm.h:824 [inline]
 kvcalloc include/linux/mm.h:829 [inline]
 xdp_umem_pin_pages net/xdp/xdp_umem.c:102 [inline]
 xdp_umem_reg net/xdp/xdp_umem.c:219 [inline]
 xdp_umem_create+0x6a5/0xf00 net/xdp/xdp_umem.c:252
 xsk_setsockopt+0x604/0x790 net/xdp/xsk.c:1068
 __sys_setsockopt+0x1fd/0x4e0 net/socket.c:2176
 __do_sys_setsockopt net/socket.c:2187 [inline]
 __se_sys_setsockopt net/socket.c:2184 [inline]
 __x64_sys_setsockopt+0xb5/0x150 net/socket.c:2184
 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

and the meaningful part of the repro is:

  syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
  syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul);
  syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
  intptr_t res = 0;
  res = syscall(__NR_socket, 0x2cul, 3ul, 0);
  if (res != -1)
    r[0] = res;
  *(uint64_t*)0x20000080 = 0;
  *(uint64_t*)0x20000088 = 0xfff02000000;
  *(uint32_t*)0x20000090 = 0x800;
  *(uint32_t*)0x20000094 = 0;
  *(uint32_t*)0x20000098 = 0;
  syscall(__NR_setsockopt, r[0], 0x11b, 4, 0x20000080ul, 0x20ul);

Willy