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.