Re: KASAN: null-ptr-deref Read in xattr_getsecurity

[Serge E. Hallyn]

On Tue, Apr 10, 2018 at 09:42:50AM -0500, Eric W. Biederman wrote:
> Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> writes:
> 
> > From 904d07a6eb014f3df0c5a1ebfcfd4323276a9a76 Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Date: Tue, 10 Apr 2018 15:15:16 +0900
> > Subject: [PATCH] commoncap: Handle memory allocation failure.
> >
> > syzbot is reporting NULL pointer dereference at xattr_getsecurity() [1],
> > for cap_inode_getsecurity() is returning sizeof(struct vfs_cap_data) when
> > memory allocation failed. Return -ENOMEM if memory allocation failed.
> >
> > [1] https://syzkaller.appspot.com/bug?id=a55ba438506fe68649a5f50d2d82d56b365e0107
> 
> Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> 
> Tetsuo I can pick this up, or do you have preferred path for getting
> this change merged?
> 
> Serge does this fix look ok to you?  I am a bit worried that

yup, looks good to me.  would have replied an hour or two ago but lacked
an lkml-acceptable mailer :)

thanks,
serge

> might be a bit brittler but I don't see any issues with this change.
> 
> Eric
> 
> 
> > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Fixes: 8db6c34f1dbc8e06 ("Introduce v3 namespaced file capabilities")
> > Reported-by: syzbot <syzbot+9369930ca44f29e60e2d@xxxxxxxxxxxxxxxxxxxxxxxxx>
> > Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.14+
> > Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
> > Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> > ---
> >  security/commoncap.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/security/commoncap.c b/security/commoncap.c
> > index 48620c9..1ce701f 100644
> > --- a/security/commoncap.c
> > +++ b/security/commoncap.c
> > @@ -449,6 +449,8 @@ int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
> >  				magic |= VFS_CAP_FLAGS_EFFECTIVE;
> >  			memcpy(&cap->data, &nscap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
> >  			cap->magic_etc = cpu_to_le32(magic);
> > +		} else {
> > +			size = -ENOMEM;
> >  		}
> >  	}
> >  	kfree(tmpbuf);
> > --
> > 1.8.3.1