linux-kernel - Re: [syzbot] [afs?] BUG: sleeping function called from invalid context in __alloc_frozen_pages

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Message-ID: <CANp29Y6gGYaQVeMHciMF5WrfueHZyWx+MJ_U4ccgJQrUyQUwog@mail.gmail.com>
Date: Mon, 31 Mar 2025 14:49:08 +0200
From: Aleksandr Nogikh <nogikh@...gle.com>
To: David Howells <dhowells@...hat.com>
Cc: syzbot <syzbot+3b6c5c6a1d0119b687a1@...kaller.appspotmail.com>, 
	linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	marc.dionne@...istor.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [afs?] BUG: sleeping function called from invalid
 context in __alloc_frozen_pages_noprof

Hi David,

Thanks for letting us know!

I've left a note in our issue tracker:
https://github.com/google/syzkaller/issues/1020#issuecomment-2766118626

On Mon, Mar 31, 2025 at 12:58 PM 'David Howells' via syzkaller-bugs
<syzkaller-bugs@...glegroups.com> wrote:
>
> Note to syzbot maintainers: the C test program contains a compressed ext3
> image and decompression code that I think is entirely unnecessary.  All it
> does is provide a directory that the afs dynroot can be mounted upon.
>
> This is the only bit of the test that is actually necessary:
>
>   NONFAILING(memcpy((void*)0x2000000001c0, "./file0\000", 8));
>   NONFAILING(memcpy((void*)0x2000000002c0, "afs\000", 4));
>   NONFAILING(memcpy((void*)0x200000000400, "dyn", 3));
>   NONFAILING(*(uint8_t*)0x200000000403 = 0x2c);
>   NONFAILING(*(uint8_t*)0x200000000404 = 0);
>   syscall(__NR_mount, /*src=*/0ul, /*dst=*/0x2000000001c0ul,
>           /*type=*/0x2000000002c0ul, /*flags=*/0ul, /*opts=*/0x200000000400ul);
>   NONFAILING(memcpy((void*)0x2000000000c0, "./file0\000", 8));
>   syscall(__NR_chdir, /*dir=*/0x2000000000c0ul);
>   NONFAILING(memcpy((void*)0x200000000240, "./file1\000", 8));
>   syscall(__NR_lstat, /*file=*/0x200000000240ul, /*statbuf=*/0ul);
>   NONFAILING(memcpy((void*)0x2000000000c0, ".\000", 2));
>   res = syscall(__NR_open, /*file=*/0x2000000000c0ul, /*flags=*/0ul,
>                 /*mode=*/0ul);
>   if (res != -1)
>     r[0] = res;
>   syscall(__NR_getdents, /*fd=*/r[0], /*ent=*/0x200000001fc0ul,
>           /*count=*/0xb8ul);
>
> Basically:
>
>   mount(NULL, "./file0", "afs", 0, "dyn,") = 0
>   chdir("./file0")                  = 0
>   lstat("./file1", NULL)            = -1 EFAULT (Bad address)
>   open(".", O_RDONLY)               = 4
>   getdents(4, 0x200000001fc0 /* 5 entries */, 184) = 168
>
> David
>

-- 
Aleksandr