From: Eric Biggers <ebigge...@gmail.com>
Date: Tue, 17 Apr 2018 12:07:06 -0700
> From: Eric Biggers <ebigg...@google.com>
>
> Adding a dns_resolver key whose payload contains a very long option name
> resulted in that string being printed in full. This hit the WARN_ONCE()
> in set_precision() during the printk(), because printk() only supports a
> precision of up to 32767 bytes:
>
> precision 1000000 too large
> WARNING: CPU: 0 PID: 752 at lib/vsprintf.c:2189 vsnprintf+0x4bc/0x5b0
>
> Fix it by limiting option strings (combined name + value) to a much more
> reasonable 128 bytes. The exact limit is arbitrary, but currently the
> only recognized option is formatted as "dnserror=%lu" which fits well
> within this limit.
>
> Also ratelimit the printks.
>
> Reproducer:
>
> perl -e 'print "#", "A" x 1000000, "\x00"' | keyctl padd dns_resolver
> desc @s
>
> This bug was found using syzkaller.
>
> Reported-by: Mark Rutland <mark.rutl...@arm.com>
> Fixes: 4a2d789267e0 ("DNS: If the DNS server returns an error, allow that to
> be cached [ver #2]")
> Signed-off-by: Eric Biggers <ebigg...@google.com>
Applied and qeueud up for -stable, thanks.
