KEYS: DNS: fix parsing multiple options
My recent fix for dns_resolver_preparse() printing very long strings was incomplete, as shown by syzbot which still managed to hit the WARN_ONCE() in set_precision() by adding a crafted "dns_resolver" key: precision 50001 too large WARNING: CPU: 7 PID: 864 at lib/vsprintf.c:2164 vsnprintf+0x48a/0x5a0 The bug this time isn't just a printing bug, but also a logical error when multiple options ("#"-separated strings) are given in the key payload. Specifically, when separating an option string into name and value, if there is no value then the name is incorrectly considered to end at the end of the key payload, rather than the end of the current option. This bypasses validation of the option length, and also means that specifying multiple options is broken -- which presumably has gone unnoticed as there is currently only one valid option anyway. A similar problem also applied to option values, as the kstrtoul() when parsing the "dnserror" option will read past the end of the current option and into the next option. Fix these bugs by correctly computing the length of the option name and by copying the option value, null-terminated, into a temporary buffer. Reproducer for the WARN_ONCE() that syzbot hit: perl -e 'print "#A#", "\0" x 50000' | keyctl padd dns_resolver desc @s Reproducer for "dnserror" option being parsed incorrectly (expected behavior is to fail when seeing the unknown option "foo", actual behavior was to read the dnserror value as "1#foo" and fail there): perl -e 'print "#dnserror=1#foo\0"' | keyctl padd dns_resolver desc @s Reported-by:syzbot <syzkaller@googlegroups.com> Fixes: 4a2d7892 ("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>
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