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.
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]")
Cc: <sta...@vger.kernel.org> # v2.6.36+
Signed-off-by: Eric Biggers <ebigg...@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);
return -EINVAL;
}
--
2.16.2.395.g2e18187dfd-goog
