linux/net/dns_resolver
Eric Biggers c210f7b411 KEYS: DNS: limit the length of option strings
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.rutland@arm.com>
Fixes: 4a2d789267 ("DNS: If the DNS server returns an error, allow that to be cached [ver #2]")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2018-04-17 13:42:58 -04:00
..
dns_key.c KEYS: DNS: limit the length of option strings 2018-04-17 13:42:58 -04:00
dns_query.c afs: Support the AFS dynamic root 2018-02-06 14:43:37 +00:00
internal.h KEYS: Merge the type-specific data with the payload data 2015-10-21 15:18:36 +01:00
Kconfig [DNS RESOLVER] Minor typo correction 2010-08-06 03:18:09 +00:00
Makefile Net: dns_resolver: Makefile: Remove deprecated kbuild goal definitions 2010-11-22 08:16:10 -08:00