proc_sysctl: fix oops caused by incorrect command parameters

The process_sysctl_arg() does not check whether val is empty before
invoking strlen(val).  If the command line parameter () is incorrectly
configured and val is empty, oops is triggered.

For example:
  "hung_task_panic=1" is incorrectly written as "hung_task_panic", oops is
  triggered. The call stack is as follows:
    Kernel command line: .... hung_task_panic
    ......
    Call trace:
    __pi_strlen+0x10/0x98
    parse_args+0x278/0x344
    do_sysctl_args+0x8c/0xfc
    kernel_init+0x5c/0xf4
    ret_from_fork+0x10/0x30

To fix it, check whether "val" is empty when "phram" is a sysctl field.
Error codes are returned in the failure branch, and error logs are
generated by parse_args().

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 3db978d480e2843 ("kernel/sysctl: support setting sysctl parameters from kernel command line")
Signed-off-by: Xiaoming Ni <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Luis Chamberlain <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Iurii Zaikin <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Heiner Kallweit <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: <[email protected]>	[5.8+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions