From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 5C0BA39D6CC for ; Tue, 21 Jul 2026 11:25:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784633153; cv=none; b=A/GMd0wEU6zBG+MYmaBcTYz0AbVxgEQlagKddlH0f82bUUOcQeMEGKdhlATlUBRFQD77DgTbDE3idVdXvGAJ4NAr6uZezIEpVu+M56Uc8DGVHJky3/hYEQUW+4PsrR/MVd0jousEDZO9Vxe6MSKTkBqJR/sdksW05J+uJ4Uba+Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784633153; c=relaxed/simple; bh=y9sSCfK1YD5juqRjlPYCrPMh1U7muN4uNZVQUKSnb2g=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=EI/KNMlqJsFPbfQQrhs+dpV56oRJWm2/rC3TNR8Kn0w51fJuDNMOBtRqQX00dMT8vIdw5ViyE+uWB67ip1NadrgUrLHXDEj4fj2IBcJ4VEbRwpCd/ROfzPm3s8xejsfOgQin1yBamcibgpwbt4++ND32+HdUTW40eLC4yqvpplo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jXegD8c5; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jXegD8c5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E6EF1F00A3A; Tue, 21 Jul 2026 11:25:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784633143; bh=OuvZWNmbh2bwBRdXFNvFwFIr3hi1+xA0mmVvYzDT3cg=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=jXegD8c5vxnyVZyYyRSlggsLf6EFsyTQ9w1zLGn8f5JSa4H0wk8q2TSlIjQNGtg/y 3Didk6ZmFL8Nub3gOHStQrL67/6O1L3xnAZyzUCfWDGWYhIrYKX+Pbe3XZLe9Fi1+C Dr5zw9w0RGoTKykjuPqw3d+UaxUh+wuhVt24P4pX9zay2u/UxGqWABm3+GA7B2tfzf JjnhgLEB8eeuv9SB6LOo1sMauoy9VILn6S9cAomy3+DtRVzsieLqQIydboi4dDfCei fkUwRW4HzVUBEW97RRKSYbzCphRduRo6/u82FoQPe/IFYi1evJ0MSLJXPKiEZ64krh m3YyDZO/G+Vyw== Message-ID: Subject: Re: [PATCH] NFSD: Map flex file layout IDs through the request's user namespace From: Jeff Layton To: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org, sashiko-bot Date: Tue, 21 Jul 2026 07:25:41 -0400 In-Reply-To: <20260720163724.810227-1-cel@kernel.org> References: <20260720163724.810227-1-cel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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init_user_ns, but every other identity > nfsd places on the wire goes through nfsd_user_namespace(). When the > transport carries a credential from a non-initial user namespace, the > flex file layout reports host-global IDs. The client copies those IDs > into the AUTH_SYS credential it presents to the data server, and > svcauth_unix_accept() resolves that credential in the transport's > namespace, so data server I/O runs under an identity unrelated to the > file's owner. >=20 > Switching to the request's namespace introduces a second hazard. > from_kuid() returns (uid_t)-1 when the target namespace has no > mapping for the owner, and the IOMODE_READ arm adds one to that > result to derive an identity for which the data server denies > writes. The addition would wrap to zero, handing the client uid 0 > instead of an identity distinct from the owner. >=20 > Translate both IDs in nfsd4_ff_proc_layoutget(), which has the > svc_rqst, and carry the wire values in struct pnfs_ff_layout. > from_kuid_munged() substitutes overflowuid for an unmapped owner and > thus never returns (uid_t)-1, so the increment cannot wrap to zero. >=20 > Fixes: 9b9960a0ca47 ("nfsd: Add a super simple flex file server") > Reported-by: sashiko-bot > Closes: https://sashiko.dev/#/patchset/20260720141442.783935-1-cel@kernel= .org?part=3D3 > Signed-off-by: Chuck Lever > --- > =C2=A0fs/nfsd/flexfilelayout.c=C2=A0=C2=A0=C2=A0 | 20 ++++++++++++-------= - > =C2=A0fs/nfsd/flexfilelayoutxdr.c |=C2=A0 4 ++-- > =C2=A0fs/nfsd/flexfilelayoutxdr.h |=C2=A0 5 +++-- > =C2=A03 files changed, 17 insertions(+), 12 deletions(-) >=20 > diff --git a/fs/nfsd/flexfilelayout.c b/fs/nfsd/flexfilelayout.c > index 9f532418cac8..c6e6b9106a83 100644 > --- a/fs/nfsd/flexfilelayout.c > +++ b/fs/nfsd/flexfilelayout.c > @@ -15,6 +15,7 @@ > =C2=A0 > =C2=A0#include "nfserr.h" > =C2=A0#include "flexfilelayoutxdr.h" > +#include "auth.h" > =C2=A0#include "pnfs.h" > =C2=A0#include "vfs.h" > =C2=A0 > @@ -24,10 +25,10 @@ static __be32 > =C2=A0nfsd4_ff_proc_layoutget(struct svc_rqst *rqstp, struct inode *inode= , > =C2=A0 const struct svc_fh *fhp, struct nfsd4_layoutget *args) > =C2=A0{ > + struct user_namespace *userns =3D nfsd_user_namespace(rqstp); > =C2=A0 struct nfsd4_layout_seg *seg =3D &args->lg_seg; > =C2=A0 u32 device_generation =3D 0; > =C2=A0 int error; > - uid_t u; > =C2=A0 > =C2=A0 struct pnfs_ff_layout *fl; > =C2=A0 > @@ -50,13 +51,16 @@ nfsd4_ff_proc_layoutget(struct svc_rqst *rqstp, struc= t inode *inode, > =C2=A0 fl->flags =3D FF_FLAGS_NO_LAYOUTCOMMIT | FF_FLAGS_NO_IO_THRU_MDS | > =C2=A0 =C2=A0=C2=A0=C2=A0 FF_FLAGS_NO_READ_IO; > =C2=A0 > - /* Do not allow a IOMODE_READ segment to have write pemissions */ > - if (seg->iomode =3D=3D IOMODE_READ) { > - u =3D from_kuid(&init_user_ns, inode->i_uid) + 1; > - fl->uid =3D make_kuid(&init_user_ns, u); > - } else > - fl->uid =3D inode->i_uid; > - fl->gid =3D inode->i_gid; > + fl->uid =3D from_kuid_munged(userns, inode->i_uid); > + fl->gid =3D from_kgid_munged(userns, inode->i_gid); > + > + /* > + * Do not allow an IOMODE_READ segment to have write permissions. > + * The group is left intact so group-readable files stay readable; > + * nfsd_setuser() squashes an unmapped uid to the export's anon ID. > + */ > + if (seg->iomode =3D=3D IOMODE_READ) > + fl->uid++; > =C2=A0 > =C2=A0 error =3D nfsd4_set_deviceid(&fl->deviceid, fhp, device_generation= ); > =C2=A0 if (error) > diff --git a/fs/nfsd/flexfilelayoutxdr.c b/fs/nfsd/flexfilelayoutxdr.c > index 97d8a28dd3a0..c12bb7c371b0 100644 > --- a/fs/nfsd/flexfilelayoutxdr.c > +++ b/fs/nfsd/flexfilelayoutxdr.c > @@ -33,8 +33,8 @@ nfsd4_ff_encode_layoutget(struct xdr_stream *xdr, > =C2=A0 > =C2=A0 fh_len =3D 4 + xdr_align_size(fl->fh.size); > =C2=A0 > - uid.len =3D sprintf(uid.buf, "%u", from_kuid(&init_user_ns, fl->uid)); > - gid.len =3D sprintf(gid.buf, "%u", from_kgid(&init_user_ns, fl->gid)); > + uid.len =3D sprintf(uid.buf, "%u", fl->uid); > + gid.len =3D sprintf(gid.buf, "%u", fl->gid); > =C2=A0 > =C2=A0 /* data server entry: deviceid + efficiency + stateid + fh list + > =C2=A0 * user + group + flags + stats_collect_hint > diff --git a/fs/nfsd/flexfilelayoutxdr.h b/fs/nfsd/flexfilelayoutxdr.h > index 6d5a1066a903..3e1876d49db2 100644 > --- a/fs/nfsd/flexfilelayoutxdr.h > +++ b/fs/nfsd/flexfilelayoutxdr.h > @@ -35,8 +35,9 @@ struct pnfs_ff_device_addr { > =C2=A0struct pnfs_ff_layout { > =C2=A0 u32 flags; > =C2=A0 u32 stats_collect_hint; > - kuid_t uid; > - kgid_t gid; > + /* Values to encode; nfsd4_ff_proc_layoutget() has mapped these */ > + u32 uid; > + u32 gid; > =C2=A0 struct nfsd4_deviceid deviceid; > =C2=A0 stateid_t stateid; > =C2=A0 struct nfs_fh fh; > -- > 2.54.0 Reviewed-by: Jeff Layton