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>
This commit is contained in:
parent
e3c1917e45
commit
c210f7b411
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@ -91,9 +91,9 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
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next_opt = memchr(opt, '#', end - opt) ?: end;
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opt_len = next_opt - opt;
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if (!opt_len) {
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printk(KERN_WARNING
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"Empty option to dns_resolver key\n");
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if (opt_len <= 0 || opt_len > 128) {
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pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
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opt_len);
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return -EINVAL;
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}
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@ -127,10 +127,8 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
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}
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bad_option_value:
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printk(KERN_WARNING
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"Option '%*.*s' to dns_resolver key:"
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" bad/missing value\n",
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opt_nlen, opt_nlen, opt);
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pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
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opt_nlen, opt_nlen, opt);
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return -EINVAL;
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} while (opt = next_opt + 1, opt < end);
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}
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