SUNRPC: fix gss_auth kref leak in gss_alloc_msg error path

In the Linux kernel, the following vulnerability has been resolved: SUNRPC: fix gss_auth kref leak in gss_alloc_msg error path Commit 5940d1cf9f42 ("SUNRPC: Rebalance a kref in auth_gss.c") added a kref_get(&gss_auth->kref) call to balance the gss_put_auth() done in gss_release_msg(), but forgot to add a corresponding kref_put() on the error path when kstrdup_const() fails. If service_name is non-NULL and kstrdup_const() fails, the function jumps to err_put_pipe_version which calls put_pipe_version() and kfree(gss_msg), but never releases the gss_auth reference. This leads to a kref leak where the gss_auth structure is never freed. Add a forward declaration for gss_free_callback() and call kref_put() in the err_put_pipe_version error path to properly release the reference taken earlier.