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Fix standalone SHA256 implementation.
authorSimon Kelley <simon@thekelleys.org.uk>
Wed, 22 Nov 2023 22:02:05 +0000 (22:02 +0000)
committerSimon Kelley <simon@thekelleys.org.uk>
Wed, 22 Nov 2023 22:02:05 +0000 (22:02 +0000)
Bug report here:
https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2023q4/017332.html

This error probably has no practical effect since even if the hash
is wrong, it's only compared internally to other hashes computed using
the same code.

Understanding the error:

hash-questions.c:168:21: runtime error: left shift of 128 by 24 places
cannot be represented in type 'int'

requires a certain amount of c-lawyerliness. I think the problem is that

m[i] = data[j] << 24

promotes the unsigned char data array value to int before doing the shift and
then promotes the result to unsigned char to match the type of m[i].
What needs to happen is to cast the unsigned char to unsigned int
BEFORE the shift.

This patch does that with explicit casts.

src/hash-questions.c patch | blob | history

diff --git a/src/hash-questions.c b/src/hash-questions.c
index c1ee135..e6304ac 100644 (file)
--- a/src/hash-questions.c
+++ b/src/hash-questions.c
@@ -165,7 +165,7 @@ static void sha256_transform(SHA256_CTX *ctx, const BYTE data[])
   WORD a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];
   
   for (i = 0, j = 0; i < 16; ++i, j += 4)
-    m[i] = (data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) | (data[j + 3]);
+    m[i] = (((WORD)data[j]) << 24) | (((WORD)data[j + 1]) << 16) | (((WORD)data[j + 2]) << 8) | (((WORD)data[j + 3]));
   for ( ; i < 64; ++i)
     m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];
 
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