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 908743D523D; Wed, 21 Jan 2026 11:45:10 +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=1768995910; cv=none; b=LuJ7tBi/0+etJyYhFyWPAzuyEps8IWP63hZvMrqrL27HKh9RczTzCCkE1UYW5JOph02BpllsJ/wVUpOfQ+zBgf5PPKsX2ff7nT8oOz7+fhAaCIsyjXYNSpwYvAH+rnC1hgo1TWocMVR2uq6BZkEH1fHhJs0WPi6RT1YA2fAPF5Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768995910; c=relaxed/simple; bh=s7nHu09ajKkt/b8xDdJdJsbZiHPFjP74+GMM0nRU7Cc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=KfFnGMpIBVi2wXVHy/w2+8xX7igNs46ErXfZByYpigsJ6nIHLsuLnpgnw1VnMkSNvsi8hz3CW4SqUysebsqYl3KR2WxRbD24+C+WYM5RfuKxkSbz0TWNt+Lnmye6ov56JWx7jR+lK0Mblex7Al0DAs6ge/YzACPDzj1H4vpmu00= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Pvw0vu64; 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="Pvw0vu64" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 381FBC116D0; Wed, 21 Jan 2026 11:45:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768995910; bh=s7nHu09ajKkt/b8xDdJdJsbZiHPFjP74+GMM0nRU7Cc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Pvw0vu64csfVSz1suDd/V/ZZQYVHWLXXpYyOcUg5LUWHFmyJXvhTIZYW+IEb/iABU GAFfw0TErIsN1YLgGF5voKvQBBraKXHCriUX5HYlwOpPIVgKzqAhAQhO+nVEeGFGB0 8XVyRY4WoLizS7rVnxTCzCZqsGgk/Dei6rrn70smbq9dXa4YC70SRrykOvNKukub2r VA/BkKGUNBrZ6fKzFjjFoglpV552fZ/v1KSwyf+izLlaaVYez0mKcUVklmNF+kvQ6n xROlY5eY+x1s6rEQX9Wqt+/LY4vMZjIyrilTuRV8wbAG+RRjZnHem2KhqwjxAz+HaF BUXQZruMIiylg== Message-ID: <43b56dc35185b0129d10840c4973485e9c305295.camel@kernel.org> Subject: Re: [PATCH] nfsd: do not allow exporting of special kernel filesystems From: Jeff Layton To: Amir Goldstein , Christian Brauner Cc: Chuck Lever , Christoph Hellwig , Neil Brown , Jan Kara , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Date: Wed, 21 Jan 2026 06:45:07 -0500 In-Reply-To: <20260121085028.558164-1-amir73il@gmail.com> References: <20260121085028.558164-1-amir73il@gmail.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ cDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQf CBYyUE8QJpvTZyfUHNYldXlrjO6n5MdOempLqWpfOmcGkwnyNRBR46g/jf8KnPRwXs509yAqDB6sE LZH+yWr9LQZEwARAQABtCVKZWZmIExheXRvbiA8amxheXRvbkBwb29jaGllcmVkcy5uZXQ+iQI7BB MBAgAlAhsDBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAUCTpXWPAIZAQAKCRAADmhBGVaCFc65D/4 gBLNMHopQYgG/9RIM3kgFCCQV0pLv0hcg1cjr+bPI5f1PzJoOVi9s0wBDHwp8+vtHgYhM54yt43uI 7Htij0RHFL5eFqoVT4TSfAg2qlvNemJEOY0e4daljjmZM7UtmpGs9NN0r9r50W82eb5Kw5bc/r0km R/arUS2st+ecRsCnwAOj6HiURwIgfDMHGPtSkoPpu3DDp/cjcYUg3HaOJuTjtGHFH963B+f+hyQ2B rQZBBE76ErgTDJ2Db9Ey0kw7VEZ4I2nnVUY9B5dE2pJFVO5HJBMp30fUGKvwaKqYCU2iAKxdmJXRI ONb7dSde8LqZahuunPDMZyMA5+mkQl7kpIpR6kVDIiqmxzRuPeiMP7O2FCUlS2DnJnRVrHmCljLkZ Wf7ZUA22wJpepBligemtSRSbqCyZ3B48zJ8g5B8xLEntPo/NknSJaYRvfEQqGxgk5kkNWMIMDkfQO lDSXZvoxqU9wFH/9jTv1/6p8dHeGM0BsbBLMqQaqnWiVt5mG92E1zkOW69LnoozE6Le+12DsNW7Rj iR5K+27MObjXEYIW7FIvNN/TQ6U1EOsdxwB8o//Yfc3p2QqPr5uS93SDDan5ehH59BnHpguTc27Xi QQZ9EGiieCUx6Zh2ze3X2UW9YNzE15uKwkkuEIj60NvQRmEDfweYfOfPVOueC+iFifbQgSmVmZiBM YXl0b24gPGpsYXl0b25AcmVkaGF0LmNvbT6JAjgEEwECACIFAk6V0q0CGwMGCwkIBwMCBhUIAgkKC wQWAgMBAh4BAheAAAoJEAAOaEEZVoIViKUQALpvsacTMWWOd7SlPFzIYy2/fjvKlfB/Xs4YdNcf9q LqF+lk2RBUHdR/dGwZpvw/OLmnZ8TryDo2zXVJNWEEUFNc7wQpl3i78r6UU/GUY/RQmOgPhs3epQC 3PMJj4xFx+VuVcf/MXgDDdBUHaCTT793hyBeDbQuciARDJAW24Q1RCmjcwWIV/pgrlFa4lAXsmhoa c8UPc82Ijrs6ivlTweFf16VBc4nSLX5FB3ls7S5noRhm5/Zsd4PGPgIHgCZcPgkAnU1S/A/rSqf3F LpU+CbVBDvlVAnOq9gfNF+QiTlOHdZVIe4gEYAU3CUjbleywQqV02BKxPVM0C5/oVjMVx3bri75n1 TkBYGmqAXy9usCkHIsG5CBHmphv9MHmqMZQVsxvCzfnI5IO1+7MoloeeW/lxuyd0pU88dZsV/riHw 87i2GJUJtVlMl5IGBNFpqoNUoqmvRfEMeXhy/kUX4Xc03I1coZIgmwLmCSXwx9MaCPFzV/dOOrju2 xjO+2sYyB5BNtxRqUEyXglpujFZqJxxau7E0eXoYgoY9gtFGsspzFkVNntamVXEWVVgzJJr/EWW0y +jNd54MfPRqH+eCGuqlnNLktSAVz1MvVRY1dxUltSlDZT7P2bUoMorIPu8p7ZCg9dyX1+9T6Muc5d Hxf/BBP/ir+3e8JTFQBFOiLNdFtB9KZWZmIExheXRvbiA8amxheXRvbkBzYW1iYS5vcmc+iQI4BBM BAgAiBQJOldK9AhsDBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRAADmhBGVaCFWgWD/0ZRi4h N9FK2BdQs9RwNnFZUr7JidAWfCrs37XrA/56olQl3ojn0fQtrP4DbTmCuh0SfMijB24psy1GnkPep naQ6VRf7Dxg/Y8muZELSOtsv2CKt3/02J1BBitrkkqmHyni5fLLYYg6fub0T/8Kwo1qGPdu1hx2BQ RERYtQ/S5d/T0cACdlzi6w8rs5f09hU9Tu4qV1JLKmBTgUWKN969HPRkxiojLQziHVyM/weR5Reu6 FZVNuVBGqBD+sfk/c98VJHjsQhYJijcsmgMb1NohAzwrBKcSGKOWJToGEO/1RkIN8tqGnYNp2G+aR 685D0chgTl1WzPRM6mFG1+n2b2RR95DxumKVpwBwdLPoCkI24JkeDJ7lXSe3uFWISstFGt0HL8Eew P8RuGC8s5h7Ct91HMNQTbjgA+Vi1foWUVXpEintAKgoywaIDlJfTZIl6Ew8ETN/7DLy8bXYgq0Xzh aKg3CnOUuGQV5/nl4OAX/3jocT5Cz/OtAiNYj5mLPeL5z2ZszjoCAH6caqsF2oLyAnLqRgDgR+wTQ T6gMhr2IRsl+cp8gPHBwQ4uZMb+X00c/Amm9VfviT+BI7B66cnC7Zv6Gvmtu2rEjWDGWPqUgccB7h dMKnKDthkA227/82tYoFiFMb/NwtgGrn5n2vwJyKN6SEoygGrNt0SI84y6hEVbQlSmVmZiBMYXl0b 24gPGpsYXl0b25AcHJpbWFyeWRhdGEuY29tPokCOQQTAQIAIwUCU4xmKQIbAwcLCQgHAwIBBhUIAg kKCwQWAgMBAh4BAheAAAoJEAAOaEEZVoIV1H0P/j4OUTwFd7BBbpoSp695qb6HqCzWMuExsp8nZjr uymMaeZbGr3OWMNEXRI1FWNHMtcMHWLP/RaDqCJil28proO+PQ/yPhsr2QqJcW4nr91tBrv/MqItu AXLYlsgXqp4BxLP67bzRJ1Bd2x0bWXurpEXY//VBOLnODqThGEcL7jouwjmnRh9FTKZfBDpFRaEfD FOXIfAkMKBa/c9TQwRpx2DPsl3eFWVCNuNGKeGsirLqCxUg5kWTxEorROppz9oU4HPicL6rRH22Ce 6nOAON2vHvhkUuO3GbffhrcsPD4DaYup4ic+DxWm+DaSSRJ+e1yJvwi6NmQ9P9UAuLG93S2MdNNbo sZ9P8k2mTOVKMc+GooI9Ve/vH8unwitwo7ORMVXhJeU6Q0X7zf3SjwDq2lBhn1DSuTsn2DbsNTiDv qrAaCvbsTsw+SZRwF85eG67eAwouYk+dnKmp1q57LDKMyzysij2oDKbcBlwB/TeX16p8+LxECv51a sjS9TInnipssssUDrHIvoTTXWcz7Y5wIngxDFwT8rPY3EggzLGfK5Zx2Q5S/N0FfmADmKknG/D8qG IcJE574D956tiUDKN4I+/g125ORR1v7bP+OIaayAvq17RP+qcAqkxc0x8iCYVCYDouDyNvWPGRhbL UO7mlBpjW9jK9e2fvZY9iw3QzIPGKtClKZWZmIExheXRvbiA8amVmZi5sYXl0b25AcHJpbWFyeWRh dGEuY29tPokCOQQTAQIAIwUCU4xmUAIbAwcLCQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEAAOa EEZVoIVzJoQALFCS6n/FHQS+hIzHIb56JbokhK0AFqoLVzLKzrnaeXhE5isWcVg0eoV2oTScIwUSU apy94if69tnUo4Q7YNt8/6yFM6hwZAxFjOXR0ciGE3Q+Z1zi49Ox51yjGMQGxlakV9ep4sV/d5a50 M+LFTmYSAFp6HY23JN9PkjVJC4PUv5DYRbOZ6Y1+TfXKBAewMVqtwT1Y+LPlfmI8dbbbuUX/kKZ5d dhV2736fgyfpslvJKYl0YifUOVy4D1G/oSycyHkJG78OvX4JKcf2kKzVvg7/Rnv+AueCfFQ6nGwPn 0P91I7TEOC4XfZ6a1K3uTp4fPPs1Wn75X7K8lzJP/p8lme40uqwAyBjk+IA5VGd+CVRiyJTpGZwA0 jwSYLyXboX+Dqm9pSYzmC9+/AE7lIgpWj+3iNisp1SWtHc4pdtQ5EU2SEz8yKvDbD0lNDbv4ljI7e flPsvN6vOrxz24mCliEco5DwhpaaSnzWnbAPXhQDWb/lUgs/JNk8dtwmvWnqCwRqElMLVisAbJmC0 BhZ/Ab4sph3EaiZfdXKhiQqSGdK4La3OTJOJYZphPdGgnkvDV9Pl1QZ0ijXQrVIy3zd6VCNaKYq7B AKidn5g/2Q8oio9Tf4XfdZ9dtwcB+bwDJFgvvDYaZ5bI3ln4V3EyW5i2NfXazz/GA/I/ZtbsigCFc 8ftCBKZWZmIExheXRvbiA8amxheXRvbkBrZXJuZWwub3JnPokCOAQTAQIAIgUCWe8u6AIbAwYLCQg HAwIGFQgCCQoLBBYCAwECHgECF4AACgkQAA5oQRlWghUuCg/+Lb/xGxZD2Q1oJVAE37uW308UpVSD 2tAMJUvFTdDbfe3zKlPDTuVsyNsALBGclPLagJ5ZTP+Vp2irAN9uwBuacBOTtmOdz4ZN2tdvNgozz uxp4CHBDVzAslUi2idy+xpsp47DWPxYFIRP3M8QG/aNW052LaPc0cedYxp8+9eiVUNpxF4SiU4i9J DfX/sn9XcfoVZIxMpCRE750zvJvcCUz9HojsrMQ1NFc7MFT1z3MOW2/RlzPcog7xvR5ENPH19ojRD CHqumUHRry+RF0lH00clzX/W8OrQJZtoBPXv9ahka/Vp7kEulcBJr1cH5Wz/WprhsIM7U9pse1f1g Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-01-21 at 09:50 +0100, Amir Goldstein wrote: > pidfs and nsfs recently gained support for encode/decode of file handles > via name_to_handle_at(2)/opan_by_handle_at(2). >=20 > These special kernel filesystems have custom ->open() and ->permission() > export methods, which nfsd does not respect and it was never meant to be > used for exporting those filesystems by nfsd. >=20 > Therefore, do not allow nfsd to export filesystems with custom ->open() > or ->permission() methods. >=20 > Fixes: b3caba8f7a34a ("pidfs: implement file handle support") > Fixes: 5222470b2fbb3 ("nsfs: support file handles") > Signed-off-by: Amir Goldstein > --- > fs/nfsd/export.c | 21 +++++++++++++-------- > 1 file changed, 13 insertions(+), 8 deletions(-) >=20 > Christian, >=20 > I had enough of the stable file handles discussion [1]. >=20 > This patch which I already suggested [2] on week ago, states a justified > technical reason why pidfs and nsfs should not be exported by nfsd, > so let's use this technical reasoning and stop the philosophic discussion= s > about what is a stable file handle is please. >=20 > Regarding cgroupfs, we can either deal with it later or not - it is not > a clear but as pidfs and nsfs which absolutely should be fixed > retroactively in stable kernels. >=20 > If you think that cgroupfs could benefit from "exhaustive" file handles [= 3] > then we can implement open_by_handle_at(FD_CGROUPFS_ROOT, ... and that > would classify cgroupfs the same as pidfs and nsfs. >=20 > Thanks, > Amir. >=20 > [1] https://lore.kernel.org/linux-fsdevel/20250912-work-namespace-v2-0-1a= 247645cef5@kernel.org/ > [2] https://lore.kernel.org/linux-fsdevel/CAOQ4uxhkaGFtQRzTj2xaf2GJucoAY5= CGiyUjB=3D8YA2zTbOtFvw@mail.gmail.com/ > [3] https://lore.kernel.org/linux-fsdevel/20250912-work-namespace-v2-29-1= a247645cef5@kernel.org/ >=20 > diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c > index 2a1499f2ad196..232dacac611e9 100644 > --- a/fs/nfsd/export.c > +++ b/fs/nfsd/export.c > @@ -405,6 +405,7 @@ static struct svc_export *svc_export_lookup(struct sv= c_export *); > static int check_export(const struct path *path, int *flags, unsigned ch= ar *uuid) > { > struct inode *inode =3D d_inode(path->dentry); > + const struct export_operations *nop =3D inode->i_sb->s_export_op; > =20 > /* > * We currently export only dirs, regular files, and (for v4 > @@ -422,13 +423,12 @@ static int check_export(const struct path *path, in= t *flags, unsigned char *uuid > if (*flags & NFSEXP_V4ROOT) > *flags |=3D NFSEXP_READONLY; > =20 > - /* There are two requirements on a filesystem to be exportable. > - * 1: We must be able to identify the filesystem from a number. > - * either a device number (so FS_REQUIRES_DEV needed) > - * or an FSID number (so NFSEXP_FSID or ->uuid is needed). > - * 2: We must be able to find an inode from a filehandle. > - * This means that s_export_op must be set. > - * 3: We must not currently be on an idmapped mount. > + /* > + * The requirements for a filesystem to be exportable: > + * 1. The filehandle must identify a filesystem by number > + * 2. The filehandle must uniquely identify an inode > + * 3. The filesystem must not have custom filehandle open/perm methods > + * 4. The requested file must not reside on an idmapped mount > */ > if (!(inode->i_sb->s_type->fs_flags & FS_REQUIRES_DEV) && > !(*flags & NFSEXP_FSID) && > @@ -437,11 +437,16 @@ static int check_export(const struct path *path, in= t *flags, unsigned char *uuid > return -EINVAL; > } > =20 > - if (!exportfs_can_decode_fh(inode->i_sb->s_export_op)) { > + if (!exportfs_can_decode_fh(nop)) { > dprintk("exp_export: export of invalid fs type.\n"); > return -EINVAL; > } > =20 > + if (nop->open || nop->permission) { > + dprintk("exp_export: export of non-standard fs type.\n"); > + return -EINVAL; > + } > + > if (is_idmapped_mnt(path->mnt)) { > dprintk("exp_export: export of idmapped mounts not yet supported.\n"); > return -EINVAL; Seems reasonable, though I agree with HCH that you should explain why we're excluding these in the "requirements" above. Reviewed-by: Jeff Layton