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 1EE42184; Fri, 11 Oct 2024 14:18:24 +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=1728656305; cv=none; b=KFBxy2PH3g6rKal+QjsY3XhhUt/aF3Qva2OsyjQE0YtOtnRSaTxdWRETGTDqSgAACXMROQz6MfjwZ05NeVURQ77px4Fg+6h5H3c0g5Hq/xM5dt9kodb7h4Hj9DVYwnrn3glXGKqF9WDL2ERfcGs5TyACOc8M5BXA80gXC3Rqu6s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728656305; c=relaxed/simple; bh=+8YToAqNQ6r0+MJdP9iaP2R0AZsZ1p2fl1SITz1MhAM=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Y6qMo7SqtWFAspNvtjd7er+nP3B4AOpdzHfPiJNJ0tfRk1GPWZPX+0q+P8RlvvgA6AIlo2gBdBEuXZVQHU5+4m0vP2uY5tVo+RbuYbXZf5uQF1xahtTYN8OPAsfo0pmrAtIzAEYEYs0TCcwP5u23yDpO8YmcS87ECR+zCgHU2dY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gwclqwX4; 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="gwclqwX4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0AF97C4CEC3; Fri, 11 Oct 2024 14:18:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728656304; bh=+8YToAqNQ6r0+MJdP9iaP2R0AZsZ1p2fl1SITz1MhAM=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=gwclqwX4m6Y8sTh4EXGTab14Votq/M83mXfcywJzEAygN+pMybNgPAxqbCLKm2cMu ixvoZHmpAcskjSzwPzcjd8DUVWnqv0D6H7Hp676vxdPvW5lZjW0gMfeeJfMz4FB0Dx x+ckt9CijByGo2CZy+u+h+M1pRyMvDSy8TLmu1zZZSIOJdZCNE3u+x0rgM0qweR3UU ZfBprt2yO2pqv6O+/LZpbjs9L4lkxNULVhOJ4BCCAlg42wxHLGiXuLnHHPD1gPZsJv IMbuHS8WuDHsaG5SBlVg7qqrFqFHVQZ8YvcWS5qFtDLFtg43wmkZo/pLL0drdUt5ib GdgJ4trnNk4Tg== Message-ID: <5ce49036cedbf7fa78a1395ded031fe2c0935e32.camel@kernel.org> Subject: Re: [PATCH v4 2/3] fs: name_to_handle_at() support for "explicit connectable" file handles From: Jeff Layton To: Amir Goldstein Cc: Christian Brauner , Jan Kara , Aleksa Sarai , Chuck Lever , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Date: Fri, 11 Oct 2024 10:18:23 -0400 In-Reply-To: References: <20241011090023.655623-1-amir73il@gmail.com> <20241011090023.655623-3-amir73il@gmail.com> <3fad10839da31f8f8b08fe355612da39a610b111.camel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Fri, 2024-10-11 at 16:14 +0200, Amir Goldstein wrote: > On Fri, Oct 11, 2024 at 4:00=E2=80=AFPM Jeff Layton = wrote: > >=20 > > On Fri, 2024-10-11 at 11:00 +0200, Amir Goldstein wrote: > > > nfsd encodes "connectable" file handles for the subtree_check feature= , > > > which can be resolved to an open file with a connected path. > > > 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 "explicitly connectable". > > >=20 > > > The "explicitly connectable" file handle sets bits in the high 16bit = of > > > the handle_type field, so open_by_handle_at(2) will know that it need= s > > > to open a file with a connected path. > > >=20 > > > old kernels will now recognize the handle_type with high bits set, > > > so "explicitly connectable" file handles cannot be decoded by > > > open_by_handle_at(2) on old kernels. > > >=20 > > > The flag AT_HANDLE_CONNECTABLE is not allowed together with either > > > AT_HANDLE_FID or AT_EMPTY_PATH. > > >=20 > > > Signed-off-by: Amir Goldstein > > > --- > > > fs/fhandle.c | 48 ++++++++++++++++++++++++++++++++++--= -- > > > include/linux/exportfs.h | 2 ++ > > > include/uapi/linux/fcntl.h | 1 + > > > 3 files changed, 46 insertions(+), 5 deletions(-) > > >=20 > > > diff --git a/fs/fhandle.c b/fs/fhandle.c > > > index 218511f38cbb..8339a1041025 100644 > > > --- a/fs/fhandle.c > > > +++ b/fs/fhandle.c > > > @@ -31,6 +31,14 @@ static long do_sys_name_to_handle(const struct pat= h *path, > > > if (!exportfs_can_encode_fh(path->dentry->d_sb->s_export_op, fh= _flags)) > > > return -EOPNOTSUPP; > > >=20 > > > + /* > > > + * A request to encode a connectable handle for a disconnected = dentry > > > + * is unexpected since AT_EMPTY_PATH is not allowed. > > > + */ > > > + if (fh_flags & EXPORT_FH_CONNECTABLE && > > > + WARN_ON(path->dentry->d_flags & DCACHE_DISCONNECTED)) > >=20 > > Is this even possible? The dentry in this case will have been reached > > by pathwalk. Oh, but I guess the dfd could point to a disconnected > > dentry and then you pass in AT_EMPTY_PATH. >=20 > But see comment above "...is unexpected since AT_EMPTY_PATH is not allowe= d." >=20 > and see below >=20 > + * AT_EMPTY_PATH could be used along with a dfd that refers to a > + * disconnected non-directory, which cannot be used to encode a > + * connectable file handle, because its parent is unknown. > + */ > + if (flag & AT_HANDLE_CONNECTABLE && > + flag & (AT_HANDLE_FID | AT_EMPTY_PATH)) > return -EINVAL; >=20 > The code/API should not allow this also for a malicious user, > unless I missed something, hence, the assertion. >=20 Ok. If that's the case, I'm fine with this as-is then. If that ever fires then I guess we'll know that something is wrong. > >=20 > > I'm not sure we want to warn in that case though, since this is a > > situation that an unprivileged user could be able to arrange. Maybe we > > should just return a more distinct error code in this case? > >=20 > > Since the scenario involves a dfd that is disconnected, how about: > >=20 > > #define EBADFD 77 /* File descriptor in bad state */ > >=20 >=20 > To me it does not look like a good fit, but let's see what others think. > In the end, it is a rare condition that should never happen > (hence assert), so I don't think the error value matters that much? >=20 Agreed. > > > + return -EINVAL; > > > + > > > if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) > > > return -EFAULT; > > >=20 > > > @@ -45,7 +53,7 @@ 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); > > > @@ -67,8 +75,23 @@ static long do_sys_name_to_handle(const struct pat= h *path, > > > * non variable part of the file_handle > > > */ > > > handle_bytes =3D 0; > > > - } else > > > + } else { > > > + /* > > > + * When asked to encode a connectable file handle, enco= de this > > > + * property in the file handle itself, so that we later= know > > > + * how to decode it. > > > + * For sanity, also encode in the file handle if the en= coded > > > + * object is a directory and verify this during decode,= because > > > + * decoding directory file handles is quite different t= han > > > + * decoding connectable non-directory file handles. > > > + */ > > > + if (fh_flags & EXPORT_FH_CONNECTABLE) { > > > + handle->handle_type |=3D FILEID_IS_CONNECTABLE; > > > + if (d_is_dir(path->dentry)) > > > + fh_flags |=3D FILEID_IS_DIR; > > > + } > > > retval =3D 0; > > > + } > > > /* copy the mount id */ > > > if (unique_mntid) { > > > if (put_user(real_mount(path->mnt)->mnt_id_unique, > > > @@ -109,15 +132,30 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, co= nst 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 han= dle > > > + * AT_HANDLE_CONNECTABLE means there is an intention to decode = a > > > + * connected fd (with known path), so these flags are conflicti= ng. > > > + * AT_EMPTY_PATH could be used along with a dfd that refers to = a > > > + * disconnected non-directory, which cannot be used to encode a > > > + * connectable file handle, because its parent is unknown. > > > + */ > > > + if (flag & AT_HANDLE_CONNECTABLE && > >=20 > > nit: might need parenthesis around the above & check. > >=20 > > > + flag & (AT_HANDLE_FID | AT_EMPTY_PATH)) >=20 > I don't think it is needed, but for readability I don't mind adding them. > I am having a hard time remembering the operation precedence myself, > but this one is clear to me so I don't bother with (). I (lately) get warnings from the compiler with W=3D1 even when the precedence is fine. If you're not seeing that then this is OK too. --=20 Jeff Layton