From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9D2F6487AE; Fri, 20 Sep 2024 07:36:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726817781; cv=none; b=bwvz1ax7scFotuFGl47MhmMgDNNCLpsSz0bmOgFR5IOIl0hbbTZN/uwkTM6qIzeefoPv52Jpaw41wOGKFByg+NcQvW/zFUTkSZXz9fDkCvpmd8rfiCKOIPx8M1X3okprN/Qm1tP70kozMf1pKIDCsA62QnpThKQ67lutt3RR2LY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726817781; c=relaxed/simple; bh=YR4pg03NL6nuT25LbAgeqe2zAdZqfsEW0BQtT7LLfmQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=LaP2B0QdNVbwY8PdCXUwKFoqVQ90zNYF/Rt16+jPkr5KXcmsviE1/a5qS6J+UzkqDaSg6LV5AlOA6tQRInSEjvnkJgIj/EWsqt6ROZbSw60/ZUZxx7rCyyFSe5nJbSIgmqNYSzfeu35mFcNnSqrVl2B23SZo2UpQf+TxNrTIh5c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PK4pXoJU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PK4pXoJU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A1258C4CECE; Fri, 20 Sep 2024 07:36:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1726817781; bh=YR4pg03NL6nuT25LbAgeqe2zAdZqfsEW0BQtT7LLfmQ=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=PK4pXoJUuP7ySmWf5MBjht0Cxo+vA+llDPcP0uGjaCM2DhewitF+yDemx+/zwkVBM v8p4gjGqofOgHO2pvlKEtzKXgi9HPq8qUtsJm98DZckY1zb51d7HkZmAGJrqnHBLsQ pwHqP3tLTO2TRD96e8q43XKafVnQufbAp3HxY1CrD0+wmbEZ/KHnxwK5Ci9MORxANK yseN1gUaTdAWg3ZeClQv91lnuOWSFbQAeFE1A94BPHbzJLSb9cL+oGRk3BxJ0i3c3x f5uYzlVsj39szDztqtLpElH819YlLk2HUkSoHIGsG4hdCWISlikeeKkjP1eObKjfXO pkIufvNDs1eyg== Message-ID: <1f8eb177bf7aa09db96c32451a14a8cdb7e31649.camel@kernel.org> Subject: Re: [RFC PATCH 1/2] fs: name_to_handle_at() support for connectable file handles From: Jeff Layton To: Amir Goldstein Cc: Christian Brauner , Aleksa Sarai , Chuck Lever , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Date: Fri, 20 Sep 2024 09:36:17 +0200 In-Reply-To: <9ab958370d5210394e5e6beaad0e788d71c42834.camel@kernel.org> References: <20240919140611.1771651-1-amir73il@gmail.com> <20240919140611.1771651-2-amir73il@gmail.com> <9ab958370d5210394e5e6beaad0e788d71c42834.camel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2024-09-20 at 09:13 +0200, Jeff Layton wrote: > On Thu, 2024-09-19 at 16:06 +0200, Amir Goldstein wrote: > > nfsd encodes "connectable" file handles for the subtree_check feature. > > So far, userspace nfs server could not make use of this functionality. > >=20 > > Introduce a new flag AT_HANDLE_CONNECTABLE to name_to_handle_at(2). > > When used, the encoded file handle is "connectable". > >=20 > > Note that decoding a "connectable" file handle with open_by_handle_at(2= ) > > is not guarandteed to return a "connected" fd (i.e. fd with known path)= . > > A new opt-in API would be needed to guarantee a "connected" fd. > >=20 > > Signed-off-by: Amir Goldstein > > --- > > fs/fhandle.c | 24 ++++++++++++++++++++---- > > include/uapi/linux/fcntl.h | 1 + > > 2 files changed, 21 insertions(+), 4 deletions(-) > >=20 > > diff --git a/fs/fhandle.c b/fs/fhandle.c > > index 8cb665629f4a..956d9b25d4f7 100644 > > --- a/fs/fhandle.c > > +++ b/fs/fhandle.c > > @@ -31,6 +31,11 @@ static long do_sys_name_to_handle(const struct path = *path, > > if (!exportfs_can_encode_fh(path->dentry->d_sb->s_export_op, fh_flags= )) > > return -EOPNOTSUPP; > > =20 > > + /* Do not encode a connectable handle for a disconnected dentry */ > > + if (fh_flags & EXPORT_FH_CONNECTABLE && > > + path->dentry->d_flags & DCACHE_DISCONNECTED) > > + return -EACCES; > > + >=20 > I'm not sure about EACCES here. That implies that if you had the right > creds then this would work. DCACHE_DISCONNECTED has nothing to do with > permissions though. Maybe -EINVAL instead since getting a disconnected > dentry here would imply that @path is somehow bogus? >=20 > Given how this function is used, will we ever see a disconnected dentry > here? The path comes from userland in this case, so I don't think it > can ever be disconnected. Maybe a WARN_ON_ONCE or pr_warn would be > appropriate in this case too? >=20 Oh, I guess you can get a disconnected dentry here. You could call open_by_handle_at() for a directory fh, and then pass that into name_to_handle_at(). Either way, this API scares me since it seems like it can just randomly fail, depending on the state of the dcache. That's the worst-case scenario for an API. If you want to go through with this, you'll need to carefully document what's required to make this work properly, as this has some significant footguns. =20 > > if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) > > return -EFAULT; > > =20 > > @@ -45,7 +50,7 @@ static long do_sys_name_to_handle(const struct path *= path, > > /* convert handle size to multiple of sizeof(u32) */ > > handle_dwords =3D f_handle.handle_bytes >> 2; > > =20 > > - /* we ask for a non connectable maybe decodeable file handle */ > > + /* Encode a possibly decodeable/connectable file handle */ > > retval =3D exportfs_encode_fh(path->dentry, > > (struct fid *)handle->f_handle, > > &handle_dwords, fh_flags); > > @@ -109,15 +114,26 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, cons= t char __user *, name, > > { > > struct path path; > > int lookup_flags; > > - int fh_flags; > > + int fh_flags =3D 0; > > int err; > > =20 > > if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID | > > - AT_HANDLE_MNT_ID_UNIQUE)) > > + AT_HANDLE_MNT_ID_UNIQUE | AT_HANDLE_CONNECTABLE)) > > + return -EINVAL; > > + > > + /* > > + * AT_HANDLE_FID means there is no intention to decode file handle > > + * AT_HANDLE_CONNECTABLE means there is an intention to decode a > > + * connected fd (with known path), so these flags are conflicting. > > + */ > > + if (flag & AT_HANDLE_CONNECTABLE && flag & AT_HANDLE_FID) > > return -EINVAL; > > + else if (flag & AT_HANDLE_FID) > > + fh_flags |=3D EXPORT_FH_FID; > > + else if (flag & AT_HANDLE_CONNECTABLE) > > + fh_flags |=3D EXPORT_FH_CONNECTABLE; > > =20 > > lookup_flags =3D (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0; > > - fh_flags =3D (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0; > > if (flag & AT_EMPTY_PATH) > > lookup_flags |=3D LOOKUP_EMPTY; > > err =3D user_path_at(dfd, name, lookup_flags, &path); > > diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h > > index 87e2dec79fea..56ff2100e021 100644 > > --- a/include/uapi/linux/fcntl.h > > +++ b/include/uapi/linux/fcntl.h > > @@ -153,6 +153,7 @@ > > object identity and may not be > > usable with open_by_handle_at(2). */ > > #define AT_HANDLE_MNT_ID_UNIQUE 0x001 /* Return the u64 unique mount I= D. */ > > +#define AT_HANDLE_CONNECTABLE 0x002 /* Request a connectable file hand= le */ > > =20 > > #if defined(__KERNEL__) > > #define AT_GETATTR_NOSEC 0x80000000 >=20 > --=20 > Jeff Layton >=20 --=20 Jeff Layton