From d09433aed821d40142b10dc5b4a0aa8110c5a09e Mon Sep 17 00:00:00 2001 From: Greg Hudson Date: Wed, 6 Nov 2024 17:31:37 -0500 Subject: [PATCH] Prevent undefined shift in decode_krb5_flags() In the statement "f |= bits[i] << (8 * (3 - i))", bits[i] is implicitly promoted from uint8_t to int according to the integer promotion rules (C99 6.3.1.1). If i is 0 and bits[i] >= 128, the result cannot be represented as an int and the behavior of the shift is undefined (C99 6.5.7). To ensure that the shift operation is defined, cast bits[i] to uint32_t. (f and the function output are int32_t, but the conversion of uint32_t to int32_t is implementation-defined when the value cannot be represented, not undefined. We check in configure.ac that the platform is two's complement.) (Discovered by OSS-Fuzz.) --- src/lib/krb5/asn.1/asn1_k_encode.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/lib/krb5/asn.1/asn1_k_encode.c b/src/lib/krb5/asn.1/asn1_k_encode.c index ad5a18a24c..1a250c98c0 100644 --- a/src/lib/krb5/asn.1/asn1_k_encode.c +++ b/src/lib/krb5/asn.1/asn1_k_encode.c @@ -250,7 +250,7 @@ decode_krb5_flags(const taginfo *t, const uint8_t *asn1, size_t len, void *val) return ret; /* Copy up to 32 bits into f, starting at the most significant byte. */ for (i = 0; i < blen && i < 4; i++) - f |= bits[i] << (8 * (3 - i)); + f |= (uint32_t)bits[i] << (8 * (3 - i)); *(krb5_flags *)val = f; free(bits); return 0; -- 2.47.2