afs: Fix the setting of the server responding flag

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: afs: Fix the setting of the server responding flag In afs_wait_for_operation(), we set transcribe the call responded flag to the server record that we used after doing the fileserver iteration loop - but it's possible to exit the loop having had a response from the server that we've discarded (e.g. it returned an abort or we started receiving data, but the call didn't complete). This means that op->server might be NULL, but we don't check that before attempting to set the server flag.

References

• https://git.kernel.org/stable/c/3d51ab44123f35dd1d646d99a15ebef10f55e263
• https://git.kernel.org/stable/c/97c953572d98080c5f1486155350bb688041747a
• https://git.kernel.org/stable/c/ff98751bae40faed1ba9c6a7287e84430f7dec64