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

* 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
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