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authorJason A. Donenfeld <Jason@zx2c4.com>2017-01-08 15:54:00 +0300
committerDavid S. Miller <davem@davemloft.net>2017-01-09 21:58:57 +0300
commit2c956a60778cbb6a27e0c7a8a52a91378c90e1d1 (patch)
treefdb29d3e887add166969e8a15c883b0c2c9ab605 /include/linux/siphash.h
parenteafea7390e597f766927d1ba7459f3904b0b9194 (diff)
downloadlinux-2c956a60778cbb6a27e0c7a8a52a91378c90e1d1.tar.xz
siphash: add cryptographically secure PRF
SipHash is a 64-bit keyed hash function that is actually a cryptographically secure PRF, like HMAC. Except SipHash is super fast, and is meant to be used as a hashtable keyed lookup function, or as a general PRF for short input use cases, such as sequence numbers or RNG chaining. For the first usage: There are a variety of attacks known as "hashtable poisoning" in which an attacker forms some data such that the hash of that data will be the same, and then preceeds to fill up all entries of a hashbucket. This is a realistic and well-known denial-of-service vector. Currently hashtables use jhash, which is fast but not secure, and some kind of rotating key scheme (or none at all, which isn't good). SipHash is meant as a replacement for jhash in these cases. There are a modicum of places in the kernel that are vulnerable to hashtable poisoning attacks, either via userspace vectors or network vectors, and there's not a reliable mechanism inside the kernel at the moment to fix it. The first step toward fixing these issues is actually getting a secure primitive into the kernel for developers to use. Then we can, bit by bit, port things over to it as deemed appropriate. While SipHash is extremely fast for a cryptographically secure function, it is likely a bit slower than the insecure jhash, and so replacements will be evaluated on a case-by-case basis based on whether or not the difference in speed is negligible and whether or not the current jhash usage poses a real security risk. For the second usage: A few places in the kernel are using MD5 or SHA1 for creating secure sequence numbers, syn cookies, port numbers, or fast random numbers. SipHash is a faster and more fitting, and more secure replacement for MD5 in those situations. Replacing MD5 and SHA1 with SipHash for these uses is obvious and straight-forward, and so is submitted along with this patch series. There shouldn't be much of a debate over its efficacy. Dozens of languages are already using this internally for their hash tables and PRFs. Some of the BSDs already use this in their kernels. SipHash is a widely known high-speed solution to a widely known set of problems, and it's time we catch-up. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Reviewed-by: Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Eric Biggers <ebiggers3@gmail.com> Cc: David Laight <David.Laight@aculab.com> Cc: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/siphash.h')
-rw-r--r--include/linux/siphash.h85
1 files changed, 85 insertions, 0 deletions
diff --git a/include/linux/siphash.h b/include/linux/siphash.h
new file mode 100644
index 000000000000..feeb29cd113e
--- /dev/null
+++ b/include/linux/siphash.h
@@ -0,0 +1,85 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ *
+ * This implementation is specifically for SipHash2-4.
+ */
+
+#ifndef _LINUX_SIPHASH_H
+#define _LINUX_SIPHASH_H
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+
+#define SIPHASH_ALIGNMENT __alignof__(u64)
+typedef struct {
+ u64 key[2];
+} siphash_key_t;
+
+u64 __siphash_aligned(const void *data, size_t len, const siphash_key_t *key);
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+u64 __siphash_unaligned(const void *data, size_t len, const siphash_key_t *key);
+#endif
+
+u64 siphash_1u64(const u64 a, const siphash_key_t *key);
+u64 siphash_2u64(const u64 a, const u64 b, const siphash_key_t *key);
+u64 siphash_3u64(const u64 a, const u64 b, const u64 c,
+ const siphash_key_t *key);
+u64 siphash_4u64(const u64 a, const u64 b, const u64 c, const u64 d,
+ const siphash_key_t *key);
+u64 siphash_1u32(const u32 a, const siphash_key_t *key);
+u64 siphash_3u32(const u32 a, const u32 b, const u32 c,
+ const siphash_key_t *key);
+
+static inline u64 siphash_2u32(const u32 a, const u32 b,
+ const siphash_key_t *key)
+{
+ return siphash_1u64((u64)b << 32 | a, key);
+}
+static inline u64 siphash_4u32(const u32 a, const u32 b, const u32 c,
+ const u32 d, const siphash_key_t *key)
+{
+ return siphash_2u64((u64)b << 32 | a, (u64)d << 32 | c, key);
+}
+
+
+static inline u64 ___siphash_aligned(const __le64 *data, size_t len,
+ const siphash_key_t *key)
+{
+ if (__builtin_constant_p(len) && len == 4)
+ return siphash_1u32(le32_to_cpup((const __le32 *)data), key);
+ if (__builtin_constant_p(len) && len == 8)
+ return siphash_1u64(le64_to_cpu(data[0]), key);
+ if (__builtin_constant_p(len) && len == 16)
+ return siphash_2u64(le64_to_cpu(data[0]), le64_to_cpu(data[1]),
+ key);
+ if (__builtin_constant_p(len) && len == 24)
+ return siphash_3u64(le64_to_cpu(data[0]), le64_to_cpu(data[1]),
+ le64_to_cpu(data[2]), key);
+ if (__builtin_constant_p(len) && len == 32)
+ return siphash_4u64(le64_to_cpu(data[0]), le64_to_cpu(data[1]),
+ le64_to_cpu(data[2]), le64_to_cpu(data[3]),
+ key);
+ return __siphash_aligned(data, len, key);
+}
+
+/**
+ * siphash - compute 64-bit siphash PRF value
+ * @data: buffer to hash
+ * @size: size of @data
+ * @key: the siphash key
+ */
+static inline u64 siphash(const void *data, size_t len,
+ const siphash_key_t *key)
+{
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+ if (!IS_ALIGNED((unsigned long)data, SIPHASH_ALIGNMENT))
+ return __siphash_unaligned(data, len, key);
+#endif
+ return ___siphash_aligned(data, len, key);
+}
+
+#endif /* _LINUX_SIPHASH_H */