[PATCH 5/6] nfsd: release OPEN-decoded posix ACLs via op_release

[Jeff Layton <jlayton@kernel.org>]

From: Chris Mason <clm@meta.com>

nfsd4_decode_createhow4() calls nfsd4_decode_fattr4(), which allocates
refcounted struct posix_acl objects via posix_acl_alloc() and stores
them in open->op_pacl and open->op_dpacl. These pointers must be
released once the OPEN compound finishes.

When nfsd4_decode_open_claim4() returns a non-seqid-mutating error,
the dispatcher short-circuits before op_func runs:

    nfsd4_proc_compound()
      opdesc->op_func == nfsd4_open_omfg
        if (!seqid_mutating_err(ntohl(op->status)))
            return op->status;   /* nfsd4_open() never runs */
      opdesc->op_release(&op->u)  /* must still release op_pacl/op_dpacl */

Before this change OP_OPEN had no .op_release in nfsd4_ops[], and the
release pair lived inside nfsd4_open() at its out_err: label. On the
short-circuit path nfsd4_open() is never invoked, so both posix_acl
refs leak on every malformed OPEN compound that carries valid POSIX
ACL createhow4 attributes.

Add nfsd4_open_release() and wire it as .op_release for OP_OPEN.
posix_acl_release() is NULL-safe, so the single release site covers
both the normal path and the nfsd4_open_omfg short-circuit. Remove
the matching posix_acl_release() pair from nfsd4_open()'s out_err:
label: the compound dispatcher calls op_release unconditionally after
every op, so leaving the in-function pair in place would double-release
op_pacl and op_dpacl on every ACL-bearing OPEN that reaches
nfsd4_open(), underflowing the refcount and freeing the posix_acl
while it is still reachable through op->u.

Fixes: 5fc51dfc2eb1 ("NFSD: Add support for XDR decoding POSIX draft ACLs")
Assisted-by: kres:claude-opus-4-7
Signed-off-by: Chris Mason <clm@meta.com>
---
 fs/nfsd/nfs4proc.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 017474cd63b5..76de265bb9e1 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -681,8 +681,6 @@ nfsd4_open(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	nfsd4_cleanup_open_state(cstate, open);
 	nfsd4_bump_seqid(cstate, status);
 out_err:
-	posix_acl_release(open->op_dpacl);
-	posix_acl_release(open->op_pacl);
 	return status;
 }
 
@@ -704,6 +702,13 @@ static __be32 nfsd4_open_omfg(struct svc_rqst *rqstp, struct nfsd4_compound_stat
 	return nfsd4_open(rqstp, cstate, &op->u);
 }
 
+static void
+nfsd4_open_release(union nfsd4_op_u *u)
+{
+	posix_acl_release(u->open.op_dpacl);
+	posix_acl_release(u->open.op_pacl);
+}
+
 /*
  * filehandle-manipulating ops.
  */
@@ -3718,6 +3723,7 @@ static const struct nfsd4_operation nfsd4_ops[] = {
 	},
 	[OP_OPEN] = {
 		.op_func = nfsd4_open,
+		.op_release = nfsd4_open_release,
 		.op_flags = OP_HANDLES_WRONGSEC | OP_MODIFIES_SOMETHING,
 		.op_name = "OP_OPEN",
 		.op_rsize_bop = nfsd4_open_rsize,

-- 
2.54.0