netdev - Re: [syzbot] KASAN: vmalloc-out-of-bounds Read in __bpf_prog

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Date:   Mon, 24 Jan 2022 12:42:16 +0100
From:   Vegard Nossum <vegard.nossum@...il.com>
To:     syzbot <syzbot+5027de09e0964fd78ce1@...kaller.appspotmail.com>
Cc:     andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
        daniel@...earbox.net, "David S. Miller" <davem@...emloft.net>,
        fgheet255t@...il.com, hawk@...nel.org, jakub@...udflare.com,
        john.fastabend@...il.com, kafai@...com, kpsingh@...nel.org,
        kuba@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        lmb@...udflare.com, Linux Netdev List <netdev@...r.kernel.org>,
        songliubraving@...com, syzkaller-bugs@...glegroups.com, yhs@...com
Subject: Re: [syzbot] KASAN: vmalloc-out-of-bounds Read in __bpf_prog_put

On Thu, 20 Jan 2022 at 15:17, syzbot
<syzbot+5027de09e0964fd78ce1@...kaller.appspotmail.com> wrote:
>
> syzbot suspects this issue was fixed by commit:
>
> commit 218d747a4142f281a256687bb513a135c905867b
> Author: John Fastabend <john.fastabend@...il.com>
> Date:   Tue Jan 4 21:46:45 2022 +0000
>
>     bpf, sockmap: Fix double bpf_prog_put on error case in map_link

I can confirm the above commit fixes the issue, but it references a
slightly different report. Looks like the only difference is
__bpf_prog_put instead of bpf_prog_put:

KASAN: vmalloc-out-of-bounds Read in __bpf_prog_put
KASAN: vmalloc-out-of-bounds Read in bpf_prog_put

However, looking at the stack traces for the two bugs shows that
__bpf_prog_put() is really the location for both reports, see:

https://syzkaller.appspot.com/bug?id=797cd651dd0d9bd921e4fa51b792f5afdc3f390f
 kasan_report.cold+0x83/0xdf mm/kasan/report.c:450 mm/kasan/report.c:450
 __bpf_prog_put.constprop.0+0x1dd/0x220 kernel/bpf/syscall.c:1812
kernel/bpf/syscall.c:1812
 bpf_prog_put kernel/bpf/syscall.c:1829 [inline]
 bpf_prog_put kernel/bpf/syscall.c:1829 [inline] kernel/bpf/syscall.c:1837

vs.

https://syzkaller.appspot.com/bug?extid=bb73e71cf4b8fd376a4f
 kasan_report+0x19a/0x1f0 mm/kasan/report.c:450 mm/kasan/report.c:450
 __bpf_prog_put kernel/bpf/syscall.c:1812 [inline]
 __bpf_prog_put kernel/bpf/syscall.c:1812 [inline] kernel/bpf/syscall.c:1829
 bpf_prog_put+0x8c/0x4f0 kernel/bpf/syscall.c:1829 kernel/bpf/syscall.c:1829

Looks to me like the compiler's inlining decision caused syzbot to see
__bpf_prog_put() instead of bpf_prog_put(), but I can't tell if it's
because it got inlined or because of the .constprop.0 suffix... I
guess syzbot skips the [inline] entries when deciding which function
to report the bug in?

In any case:

#syz dup: KASAN: vmalloc-out-of-bounds Read in bpf_prog_put


Vegard