linux-kernel - Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

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Message-Id: <E1Jp3DA-00048z-Vl@pomaz-ex.szeredi.hu>
Date:	Thu, 24 Apr 2008 17:18:12 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@...IV.linux.org.uk
CC:	miklos@...redi.hu, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, dave@...ux.vnet.ibm.com,
	ezk@...sunysb.edu, mhalcrow@...ibm.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

> > > > > RTFS.  permission() doesn't do "is that vfsmount read-only" checks, exactly
> > > > > because it's 100% bogus - either you cover it with entire area where we
> > > > > are guaranteed to stay r/w, or it's by definition racy.
> > > > 
> > > > I know that.
> > > > 
> > > > That does not mean, that fh_verify() needs to do vfsmount r/o checks.
> > > > AFAICS it's perfectly OK to do that later, around the vfs_ call.
> > > 
> > > ... and around everything else that happens to be done after fh_verify
> > > for write access, surely?
> >
> > What in particular?  You have managed to avoid answering this question
> > for the last...I don't know how many emails.
> 
> Oh, for fuck sake...  grep and ye shall see.  Right next to setattr we
> have nfsd4_set_nfs4_acl(), with pair of set_nfsv4_acl_one().  I'd rather
> have those two covered by a single will/wont range, TYVM.
> 
> nfsd_create() will happily do vfs_mkdir() and nfsd_create_setattr().  Ditto.

Please read the patches?  I've left exactly these
mnt_want_write/drop_write() calls in place, and removed all the
others.

> And while we are at it, losing the check for r/o in fh_verify() will sure
> as hell require at least handling it separately on the normal write path.

Umm, no, dentry_open() will do that.

> 
> > >  Note that e.g. nfsd_setattr() does _not_ call
> > > vfs_<anything>()...
> > 
> > Yes it does: notify_change().  It's vfs_setattr() under a pseudonym.
> 
> Are you going to move the will/wont in there?  Because there's a bunch of
> stuff in fs/open.c that will disagree...

Please read the patches, won't you?

Miklos
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