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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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