Re: [PATCH] mm/slub: fix to return errno if kmalloc() fails

[Marion & Christophe JAILLET]

Le 13/09/2022 à 05:42, Chao Yu a écrit :
> On 2022/9/10 0:47, Christophe JAILLET wrote:
> > Le 30/08/2022 à 16:10, Chao Yu a écrit :
> > > From: Chao Yu <chao.yu@xxxxxxxx>
> > >
> > > In create_unique_id(), kmalloc(, GFP_KERNEL) can fail due to
> > > out-of-memory, if it fails, return errno correctly rather than
> > > triggering panic via BUG_ON();
> > >
> > > kernel BUG at mm/slub.c:5893!
> > > Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> > >
> > > Call trace:
[...]
> > > Cc: <stable@xxxxxxxxxx>
> > > Reported-by: syzbot+81684812ea68216e08c5@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > Signed-off-by: Chao Yu <chao.yu@xxxxxxxx>
> > > ---
> > >   mm/slub.c | 5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index 862dbd9af4f5..e6f3727b9ad2 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -5890,7 +5890,8 @@ static char *create_unique_id(struct 
> > > kmem_cache *s)
> > >       char *name = kmalloc(ID_STR_LENGTH, GFP_KERNEL);
> >
> > Hi,
> >
> > looks that ID_STR_LENGTH could even be reduced to 32 or 16.
> >
> > The 2nd BUG_ON at the end of the function could certainly be just 
> > removed as well or remplaced by a:
> >         if (p > name + ID_STR_LENGTH - 1) {
> >          kfree(name);
> >          return -E<something>;
> >      }
>
> Hi Christophe, Vlastimil,
>
> Should I include this in v3? or may be in another patch?

Hi,

My own preference would be for 3 patches.

Yours, as-is.
It fixes a specific issue spotted by syzbot.

Another one for removing a BUG_ON() (that, IIUC can't happen!)
Mostly a clean-up or a good practice in order to remove BUG_ON() from 
the kernel we it can be handled another way.

Eventually a 3rd one for reducing ID_STR_LENGTH.
I guess that it is safe to reduce it to 32 or 16, but the impact on RL 
would be so small, that I wonder if it worth proposing it.

Just my 2c,

CJ



> Thanks,
>
> > Just my 2c,
> >
> > CJ
> >
> > >       char *p = name;
> > > -    BUG_ON(!name);
> > > +    if (!name)
> > > +        return ERR_PTR(-ENOMEM);
> > >       *p++ = ':';
> > >       /*
> > > @@ -5948,6 +5949,8 @@ static int sysfs_slab_add(struct kmem_cache *s)
> > >            * for the symlinks.
> > >            */
> > >           name = create_unique_id(s);
> > > +        if (IS_ERR(name))
> > > +            return PTR_ERR(name);
> > >       }
> > >       s->kobj.kset = kset;