Re: [PATCH] Prevent crash on missing sysfs attribute group

[Ingo Molnar <mingo@kernel.org>]

* Bruno Prémont <bonbons@linux-vserver.org> wrote:

> Prevent kernel from crashing when a device is being registered with sysfs
> but has no (aka NULL) group attributes, but warn about it so calling path
> can get fixed.
> 
> This would warn instead of trying NULL pointer deref like:
>  BUG: unable to handle kernel NULL pointer dereference at           (null)
>  IP: [<ffffffff81152673>] internal_create_group+0x83/0x1a0
>  PGD 0 
>  Oops: 0000 [#1] SMP 
>  CPU 0 
>  Modules linked in:
> 
>  Pid: 1, comm: swapper/0 Not tainted 3.4.0-rc1-x86_64 #3 HP ProLiant DL360 G4
>  RIP: 0010:[<ffffffff81152673>]  [<ffffffff81152673>] internal_create_group+0x83/0x1a0
>  RSP: 0018:ffff88019485fd70  EFLAGS: 00010202
>  RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000001
>  RDX: ffff880192e99908 RSI: ffff880192e99630 RDI: ffffffff81a26c60
>  RBP: ffff88019485fdc0 R08: 0000000000000000 R09: 0000000000000000
>  R10: ffff880192e99908 R11: 0000000000000000 R12: ffffffff81a16a00
>  R13: ffff880192e99908 R14: ffffffff81a16900 R15: 0000000000000000
>  FS:  0000000000000000(0000) GS:ffff88019bc00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>  CR2: 0000000000000000 CR3: 0000000001a0c000 CR4: 00000000000007f0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>  Process swapper/0 (pid: 1, threadinfo ffff88019485e000, task ffff880194878000)
>  Stack:
>   ffff88019485fdd0 ffff880192da9d60 0000000000000000 ffff880192e99908
>   ffff880192e995d8 0000000000000001 ffffffff81a16a00 ffff880192da9d60
>   0000000000000000 0000000000000000 ffff88019485fdd0 ffffffff811527be
>  Call Trace:
>   [<ffffffff811527be>] sysfs_create_group+0xe/0x10
>   [<ffffffff81376ca6>] device_add_groups+0x46/0x80
>   [<ffffffff81377d3d>] device_add+0x46d/0x6a0
>   ...
> 
> Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
> ---
> On Tue, 3 Apr 2012 08:02:52 +0200 Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > > On Mon, 2012-04-02 at 23:24 +0200, Peter Zijlstra wrote:
> > > > On Mon, 2012-04-02 at 21:34 +0200, Bruno Prémont wrote:
> > > > > > >> [    0.996198] Pid: 1, comm: swapper/0 Not tainted 3.4.0-rc1-x86_64 #3 HP ProLiant DL360 G4
> > > > 
> > > > Is this a netburst based space heater?
> > > 
> > > In particular, does: https://lkml.org/lkml/2012/3/27/182 , sort it?
> > > 
> > > Ingo, could you pick that one up and route it Linus wards?
> > 
> > Will do - but the underlying generic bug should be fixed as 
> > well: we must not crash just because some attributes are missing 
> > in a rarely used sub-driver ...
> > 
> > We should WARN_ON(), etc. - but not crash.
> 
> Greg, is this ok for you or should the check be moved out to calling
> internal_create_group()?
> 
> ---
> diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
> index dd1701c..0040ff2 100644
> --- a/fs/sysfs/group.c
> +++ b/fs/sysfs/group.c
> @@ -32,7 +32,8 @@ static int create_files(struct sysfs_dirent *dir_sd, struct kobject *kobj,
>  	struct attribute *const* attr;
>  	int error = 0, i;
>  
> -	for (i = 0, attr = grp->attrs; *attr && !error; i++, attr++) {
> +	WARN_ON(!grp->attrs);
> +	for (i = 0, attr = grp->attrs; attr && *attr && !error; i++, attr++) {
>  		umode_t mode = 0;

yeah.

Acked-by: Ingo Molnar <mingo@elte.hu>

Thanks,

	Ingo