| Message ID | 20180228014905.68153-1-ebiggers3@gmail.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | KEYS: DNS: limit the length of option strings | expand |
On Tue, 2018-02-27 at 17:49 -0800, Eric Biggers wrote: > From: Eric Biggers <ebiggers@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. > > 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]") > Cc: <stable@vger.kernel.org> # v2.6.36+ > Signed-off-by: Eric Biggers <ebiggers@google.com> > --- > net/dns_resolver/dns_key.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c > index e1d4d898a007..7c0aae2e512d 100644 > --- a/net/dns_resolver/dns_key.c > +++ b/net/dns_resolver/dns_key.c > @@ -91,9 +91,9 @@ dns_resolver_preparse(struct key_preparsed_payload *prep) > > next_opt = memchr(opt, '#', end - opt) ?: end; > opt_len = next_opt - opt; > - if (!opt_len) { > - printk(KERN_WARNING > - "Empty option to dns_resolver key\n"); > + if (opt_len <= 0 || opt_len > 128) { > + pr_warn("Invalid option length (%d) for dns_resolver key\n", > + opt_len); If a bot can harass us here, then pr_warn_ratelimited would be nice ?
On Tue, Feb 27, 2018 at 06:34:19PM -0800, Eric Dumazet wrote: > On Tue, 2018-02-27 at 17:49 -0800, Eric Biggers wrote: > > From: Eric Biggers <ebiggers@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. > > > > 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]") > > Cc: <stable@vger.kernel.org> # v2.6.36+ > > Signed-off-by: Eric Biggers <ebiggers@google.com> > > --- > > net/dns_resolver/dns_key.c | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c > > index e1d4d898a007..7c0aae2e512d 100644 > > --- a/net/dns_resolver/dns_key.c > > +++ b/net/dns_resolver/dns_key.c > > @@ -91,9 +91,9 @@ dns_resolver_preparse(struct key_preparsed_payload *prep) > > > > next_opt = memchr(opt, '#', end - opt) ?: end; > > opt_len = next_opt - opt; > > - if (!opt_len) { > > - printk(KERN_WARNING > > - "Empty option to dns_resolver key\n"); > > + if (opt_len <= 0 || opt_len > 128) { > > + pr_warn("Invalid option length (%d) for dns_resolver key\n", > > + opt_len); > > If a bot can harass us here, then pr_warn_ratelimited would be nice ? > I guess we might as well. But there is another user-triggerable printk just below, so I'll need to change that one too. I'll send out v2. Eric
diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c index e1d4d898a007..7c0aae2e512d 100644 --- a/net/dns_resolver/dns_key.c +++ b/net/dns_resolver/dns_key.c @@ -91,9 +91,9 @@ dns_resolver_preparse(struct key_preparsed_payload *prep) next_opt = memchr(opt, '#', end - opt) ?: end; opt_len = next_opt - opt; - if (!opt_len) { - printk(KERN_WARNING - "Empty option to dns_resolver key\n"); + if (opt_len <= 0 || opt_len > 128) { + pr_warn("Invalid option length (%d) for dns_resolver key\n", + opt_len); return -EINVAL; }