[PATCH] vmcoreinfo: Warn if we exceed vmcoreinfo data size

[Baoquan He]

On 10/27/22 at 01:50pm, Stephen Brennan wrote:
> Though vmcoreinfo is intended to be small, at just one page, useful
> information is still added to it, so we risk running out of space.
> Currently there is no runtime check to see whether the vmcoreinfo buffer
> has been exhausted. Add a warning for this case.
> 
> Currently, my static checking tool[1] indicates that a good upper bound
> for vmcoreinfo size is currently 3415 bytes, but the best time to add
> warnings is before the risk becomes too high.
> 
> [1] https://github.com/brenns10/kernel_stuff/blob/master/vmcoreinfosize/vmcoreinfosize.py
> 
> Signed-off-by: Stephen Brennan <stephen.s.brennan at oracle.com>
> ---
>  kernel/crash_core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index a0eb4d5cf557..87ef6096823f 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -383,6 +383,9 @@ void vmcoreinfo_append_str(const char *fmt, ...)
>  	memcpy(&vmcoreinfo_data[vmcoreinfo_size], buf, r);
>  
>  	vmcoreinfo_size += r;
> +
> +	WARN_ONCE(vmcoreinfo_size == VMCOREINFO_BYTES,
> +		  "vmcoreinfo data exceeds allocated size, truncating");
>  }

Yeah, sounds like a good idea. Thanks.

Acked-by: Baoquan He <bhe at redhat.com>