github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-09-25 17:42:03 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref

Browse Source 
When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return
success with fh_dentry and fh_export both NULL if fh_verify() returns
nfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag
is set, but the compound dispatch loop only uses this flag to bypass
the nfserr_nofilehandle check -- it does not prevent subsequent ops
from running with a NULL fh_dentry.

A remote client can exploit this by crafting a COMPOUND that includes
an inter-SSC COPY (which causes check_if_stalefh_allowed() to set
no_verify=true on the saved PUTFH) with an additional op inserted
between the source PUTFH and SAVEFH. For example, SETATTR calls
fh_want_write() which dereferences fh_export->ex_path.mnt without
calling fh_verify() first, causing a NULL pointer dereference in the
nfsd kthread.

Fix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set
and fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow)
and ops with ALLOWED_WITHOUT_FH (which don't need a resolved
filehandle) may proceed. All other ops receive nfserr_stale, per
RFC 7862 Section 15.2.3 which specifies that foreign filehandle
validation is deferred to the consuming operation and NFS4ERR_STALE
returned at that point.

Fixes: b9e8638e3d ("NFSD: allow inter server COPY to have a STALE source server fh")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260527-putfh_foreign_fh_null_deref_consumers-v1-1-1b8a5aa28c59@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Jeff Layton 2026-05-27 10:53:37 -04:00 committed by Chuck Lever
parent f42d0fda0c
commit c59738a00a
1 changed files with 16 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
fs/nfsd/nfs4proc.c
View File

@ -3125,9 +3125,22 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
op->status = nfsd4_open_omfg(rqstp, cstate, op);
goto encode_op;
}
if (!current_fh->fh_dentry &&
!HAS_FH_FLAG(current_fh, NFSD4_FH_FOREIGN)) {
if (!(op->opdesc->op_flags & ALLOWED_WITHOUT_FH)) {
if (!current_fh->fh_dentry) {
if (HAS_FH_FLAG(current_fh, NFSD4_FH_FOREIGN)) {
/*
* FOREIGN fh from inter-SSC PUTFH: only
* SAVEFH may proceed with a NULL fh_dentry.
* Per RFC 7862 S15.2.3, validation of a
* foreign fh is deferred to the operation
* that consumes it, and NFS4ERR_STALE is
* returned at that point.
*/
if (op->opnum != OP_SAVEFH &&
!(op->opdesc->op_flags & ALLOWED_WITHOUT_FH)) {
op->status = nfserr_stale;
goto encode_op;
}
} else if (!(op->opdesc->op_flags & ALLOWED_WITHOUT_FH)) {
op->status = nfserr_nofilehandle;
goto encode_op;
}