SUNRPC: reject duplicate CREDS_VALUE options

gssx_dec_option_array() walks the wire-supplied option array and, for
every entry whose name matches CREDS_VALUE, calls
gssx_dec_linux_creds() on the same struct svc_cred. That helper
unconditionally installs a fresh groups_alloc() result into
creds->cr_group_info without releasing whatever pointer was already
there:

    for (i = 0; i < count; i++) {
        ... decode name ...
        if (length == sizeof(CREDS_VALUE) &&
            memcmp(p, CREDS_VALUE, sizeof(CREDS_VALUE)) == 0) {
            err = gssx_dec_linux_creds(xdr, creds);
            ...
        }
    }

A reply that carries two CREDS_VALUE entries therefore overwrites
cr_group_info on the second iteration and orphans the group_info
allocated by the first call. The earlier free_creds path only
releases the last cr_group_info via free_svc_cred(), so the first
allocation's refcount stays at one and its kvmalloc-backed storage
is leaked. No in-tree caller of gssp_accept_sec_context_upcall()
expects more than one CREDS_VALUE per reply.

Fix by tracking whether a CREDS_VALUE option has already been
decoded and returning -EINVAL on any subsequent match, so the
free_creds path releases the single group_info that was installed.

Fixes: 1d658336b05f ("SUNRPC: Add RPC based upcall mechanism for RPCGSS auth")
Cc: stable@vger.kernel.org
Assisted-by: kres (claude-opus-4-7)
Signed-off-by: Chris Mason <clm@meta.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260528-tier2-v1-3-d026a1415e0b@oracle.com
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c b/net/sunrpc/auth_gss/gss_rpc_xdr.c
index f2b8f919adea..0549edae1ebe 100644
--- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
+++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
@@ -231,6 +231,7 @@ static int gssx_dec_option_array(struct xdr_stream *xdr,
 				 struct gssx_option_array *oa)
 {
 	struct svc_cred *creds;
+	bool creds_decoded = false;
 	u32 count, i;
 	__be32 *p;
 	int err;
@@ -281,9 +282,14 @@ static int gssx_dec_option_array(struct xdr_stream *xdr,
 		if (length == sizeof(CREDS_VALUE) &&
 		    memcmp(p, CREDS_VALUE, sizeof(CREDS_VALUE)) == 0) {
 			/* We have creds here. parse them */
+			if (creds_decoded) {
+				err = -EINVAL;
+				goto free_creds;
+			}
 			err = gssx_dec_linux_creds(xdr, creds);
 			if (err)
 				goto free_creds;
+			creds_decoded = true;
 			oa->data[0].value.len = 1; /* presence */
 		} else {
 			/* consume uninteresting buffer */