In the Linux kernel, the following vulnerability has been resolved: s390/boot: Avoid IPL parameter append past command line A command line

In the Linux kernel, the following vulnerability has been resolved:

s390/boot: Avoid IPL parameter append past command line

A command line may occupy all but the terminating byte of
COMMAND_LINE_SIZE. In that case append_ipl_block_parm() passes a zero size
to the IPL parameter conversion helpers and points the destination one
byte past early_command_line. The helpers subtract one from the unsigned
size and write the converted parameter outside the command line buffer.

Convert the IPL parameter in the command line parsing buffer first. A
parameter beginning with '=' can then replace the existing command line
regardless of its length, while other parameters are appended only when
space remains.