SUNRPC: fix a memleak in gss_import_v2_context

The ctx->mech_used.data allocated by kmemdup is not freed in neither
gss_import_v2_context nor it only caller gss_krb5_import_sec_context,
which frees ctx on error.

Thus, this patch reform the last call of gss_import_v2_context to the
gss_krb5_import_ctx_v2, preventing the memleak while keepping the return
formation.

Fixes: 47d8480 ("gss_krb5: handle new context format from gssd")
Signed-off-by: Zhipeng Lu <alexious@zju.edu.cn>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/auth_gss/gss_krb5_mech.c

@@ -398,6 +398,7 @@ gss_import_v2_context(const void *p, const void *end, struct krb5_ctx *ctx,
 	u64 seq_send64;
 	int keylen;
 	u32 time32;
+	int ret;
 
 	p = simple_get_bytes(p, end, &ctx->flags, sizeof(ctx->flags));
 	if (IS_ERR(p))
@@ -450,8 +451,16 @@ gss_import_v2_context(const void *p, const void *end, struct krb5_ctx *ctx,
 	}
 	ctx->mech_used.len = gss_kerberos_mech.gm_oid.len;
 
-	return gss_krb5_import_ctx_v2(ctx, gfp_mask);
+	ret = gss_krb5_import_ctx_v2(ctx, gfp_mask);
+	if (ret) {
+		p = ERR_PTR(ret);
+		goto out_free;
+	}
 
+	return 0;
+
+out_free:
+	kfree(ctx->mech_used.data);
 out_err:
 	return PTR_ERR(p);
 }