3.16.60-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Biggers ebiggers@google.com
commit 9c438d7a3a52dcc2b9ed095cb87d3a5e83cf7e60 upstream.
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: 4a2d789267e0 ("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 [bwh: Backported to 3.16: - Also stop logging the key serial number - Include <linux/ratelimit.h> directly] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/net/dns_resolver/dns_key.c +++ b/net/dns_resolver/dns_key.c @@ -29,6 +29,7 @@ #include <linux/keyctl.h> #include <linux/err.h> #include <linux/seq_file.h> +#include <linux/ratelimit.h> #include <keys/dns_resolver-type.h> #include <keys/user-type.h> #include "internal.h" @@ -93,10 +94,9 @@ dns_resolver_instantiate(struct key *key
next_opt = memchr(opt, '#', end - opt) ?: end; opt_len = next_opt - opt; - if (!opt_len) { - printk(KERN_WARNING - "Empty option to dns_resolver key %d\n", - key->serial); + if (opt_len <= 0 || opt_len > 128) { + pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n", + opt_len); return -EINVAL; }
@@ -130,10 +130,8 @@ dns_resolver_instantiate(struct key *key }
bad_option_value: - printk(KERN_WARNING - "Option '%*.*s' to dns_resolver key %d:" - " bad/missing value\n", - opt_nlen, opt_nlen, opt, key->serial); + pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n", + opt_nlen, opt_nlen, opt); return -EINVAL; } while (opt = next_opt + 1, opt < end); }