Re: fs: GPF in bd_mount

[Mateusz Guzik]

On Sun, Sep 04, 2016 at 12:43:28PM +0200, Dmitry Vyukov wrote:
> Hello,
> 
> The following program triggers GPF in bd_mount:
> 
> 
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <fcntl.h>
> #include <sys/stat.h>
> #include <sys/types.h>
> #include <unistd.h>
> #include <sched.h>
> #include <linux/sched.h>
> 
> int main()
> {
>   int fd;
> 
>   unshare(CLONE_NEWUSER);
>   unshare(CLONE_NEWNS);
>   mkdir("./bus", 0662515705056234013740);
>   mount("./bus/bus", "./bus", "bdev", 0,
>       "\xa9\x95\xbd\x88\x07\x6a\x39\xe8\xf4\xef\xf2\x6b\x88\x53\x1d\xdb"
>       "\xd2\x83\xf9\x5f\x4f\x44\x71\xf2\x08\x84\x2b\xae\x94\x87\xb7\xa6"
>       "\xf8\x9d\xc9\x96\xc7\x17\x2e\x22\xc4\xd2\xcc\xf9\x04\x0b\xd2\xaf"
>       "\xf3\x0b\xec\xeb\x2b\x75\xf2\x93\xa2\xd4\x00\xd8\x69\x47\x48\xf5"
>       "\xaf\x2b\xb8\x7c\x06\x04\x69\x8b\x46\x0d\x44\x79\x8c\x86\x68\xfd"
>       "\xd3\xb4\x1c\x8e\x9e\x6c\x58\x0c\xa5\xdf\x55\x4d\x59\x65\xc9\x70"
>       "\x7c\x8a\x44\x26\x7d\xba\xf0\x3d\x46\x9e\x3c\xbe\x22\xc3");
>   return 0;
> }
> 
> 
> general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
> Modules linked in:
> CPU: 2 PID: 4052 Comm: a.out Not tainted 4.8.0-rc3-next-20160825+ #11
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff88006b37a380 task.stack: ffff880066dc0000
> RIP: 0010:[<ffffffff81927582>]  [<ffffffff81927582>]
> bd_mount+0x52/0xa0 fs/block_dev.c:650
> RSP: 0018:ffff880066dc7ca0  EFLAGS: 00010207
> RAX: dffffc0000000000 RBX: ffffffffffffffff RCX: 0000000000000001
> RDX: 0000000000000018 RSI: ffffffff886fd6c0 RDI: 00000000000000c7
> RBP: ffff880066dc7cb0 R08: ffff88006b642cb8 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8880d440
> R13: ffff88006a4ac1c0 R14: ffff88006b64b000 R15: 0000000000000000
> FS:  00000000012b2880(0000) GS:ffff88006d200000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000004b2160 CR3: 000000006cc72000 CR4: 00000000000006e0
> Stack:
>  ffff880068e2c840 ffffffff8880d440 ffff880066dc7cf0 ffffffff8186e73b
>  0000000000000004 ffff88006659c600 ffffffff8880d440 ffff88006a4ac1c0
>  0000000000000000 ffff880068e2c840 ffff880066dc7d40 ffffffff818ce44a
> Call Trace:
>  [<ffffffff8186e73b>] mount_fs+0x9b/0x2f0 fs/super.c:1177
>  [<ffffffff818ce44a>] vfs_kern_mount+0x7a/0x3e0 fs/namespace.c:948
>  [<     inline     >] do_new_mount fs/namespace.c:2393
>  [<ffffffff818d6255>] do_mount+0x3d5/0x26b0 fs/namespace.c:2715
>  [<     inline     >] SYSC_mount fs/namespace.c:2907
>  [<ffffffff818d8f6b>] SyS_mount+0xab/0x120 fs/namespace.c:2884
>  [<ffffffff810088ff>] do_syscall_64+0x1df/0x640 arch/x86/entry/common.c:288
>  [<ffffffff86e10543>] entry_SYSCALL64_slow_path+0x25/0x25
> arch/x86/entry/entry_64.S:249
> Code: 87 e8 f3 ca fb ff 48 85 c0 48 89 c3 74 4c e8 a6 47 ca ff 48 8d
> bb c8 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80>
> 3c 02 00 75 36 4c 8b a3 c8 00 00 00 48 b8 00 00 00 00 00 fc
> RIP  [<ffffffff81927582>] bd_mount+0x52/0xa0 fs/block_dev.c:650
>  RSP <ffff880066dc7ca0>
> ---[ end trace 0e5d909159d79633 ]---
> 
> 
> On commit 0f98f121e1670eaa2a2fbb675e07d6ba7f0e146f of linux-next.
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I think this is fixed with:
commit e9e5e3fae8da7e237049e00e0bfc9e32fd808fe8
Author: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Date:   Mon Aug 22 12:47:43 2016 +0200

    bdev: fix NULL pointer dereference

in mainline. The commit is absent in linux-next.

-- 
Mateusz Guzik