From f913d5d2130a584d1a027ffe3dfd88b6be2e0540 Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Mon, 20 Jul 2026 12:37:24 -0400 Subject: [PATCH] NFSD: Map flex file layout IDs through the request's user namespace nfsd4_ff_proc_layoutget() and nfsd4_ff_encode_layoutget() translate the file's owner and group with 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. 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. 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. Fixes: 9b9960a0ca47 ("nfsd: Add a super simple flex file server") Cc: stable@vger.kernel.org Reported-by: sashiko-bot Closes: https://sashiko.dev/#/patchset/20260720141442.783935-1-cel@kernel.org?part=3 Reviewed-by: Jeff Layton Link: https://patch.msgid.link/20260720163724.810227-1-cel@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/flexfilelayout.c | 20 ++++++++++++-------- fs/nfsd/flexfilelayoutxdr.c | 4 ++-- fs/nfsd/flexfilelayoutxdr.h | 5 +++-- 3 files changed, 17 insertions(+), 12 deletions(-) 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 @@ #include "nfserr.h" #include "flexfilelayoutxdr.h" +#include "auth.h" #include "pnfs.h" #include "vfs.h" @@ -24,10 +25,10 @@ static __be32 nfsd4_ff_proc_layoutget(struct svc_rqst *rqstp, struct inode *inode, const struct svc_fh *fhp, struct nfsd4_layoutget *args) { + struct user_namespace *userns = nfsd_user_namespace(rqstp); struct nfsd4_layout_seg *seg = &args->lg_seg; u32 device_generation = 0; int error; - uid_t u; struct pnfs_ff_layout *fl; @@ -50,13 +51,16 @@ nfsd4_ff_proc_layoutget(struct svc_rqst *rqstp, struct inode *inode, fl->flags = FF_FLAGS_NO_LAYOUTCOMMIT | FF_FLAGS_NO_IO_THRU_MDS | FF_FLAGS_NO_READ_IO; - /* Do not allow a IOMODE_READ segment to have write pemissions */ - if (seg->iomode == IOMODE_READ) { - u = from_kuid(&init_user_ns, inode->i_uid) + 1; - fl->uid = make_kuid(&init_user_ns, u); - } else - fl->uid = inode->i_uid; - fl->gid = inode->i_gid; + fl->uid = from_kuid_munged(userns, inode->i_uid); + fl->gid = 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 == IOMODE_READ) + fl->uid++; error = nfsd4_set_deviceid(&fl->deviceid, fhp, device_generation); 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, fh_len = 4 + xdr_align_size(fl->fh.size); - uid.len = sprintf(uid.buf, "%u", from_kuid(&init_user_ns, fl->uid)); - gid.len = sprintf(gid.buf, "%u", from_kgid(&init_user_ns, fl->gid)); + uid.len = sprintf(uid.buf, "%u", fl->uid); + gid.len = sprintf(gid.buf, "%u", fl->gid); /* data server entry: deviceid + efficiency + stateid + fh list + * 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 { struct pnfs_ff_layout { u32 flags; u32 stats_collect_hint; - kuid_t uid; - kgid_t gid; + /* Values to encode; nfsd4_ff_proc_layoutget() has mapped these */ + u32 uid; + u32 gid; struct nfsd4_deviceid deviceid; stateid_t stateid; struct nfs_fh fh;