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[XPCOM] Fix Base64 off-by-one issue and safeguard against this mistake in the future.

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Moonchild 2022-10-26 09:24:27 +00:00 • committed by roytam1
commit 3fccd404fb
1 changed files with 9 additions and 3 deletions
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12
xpcom/io/Base64.cpp
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@ -246,6 +246,7 @@ EncodeInputStream(nsIInputStream* aInputStream,
static const char kBase64URLAlphabet[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
static_assert(mozilla::ArrayLength(kBase64URLAlphabet) == 0x41);
// Maps an encoded character to a value in the Base64 URL alphabet, per
// RFC 4648, Table 2. Invalid input characters map to UINT8_MAX.
@ -267,14 +268,19 @@ static const uint8_t kBase64URLDecodeTable[] = {
255,
26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41,
42, 43, 44, 45, 46, 47, 48, 49, 50, 51, /* a - z */
255, 255, 255, 255,
255, 255, 255, 255, 255
};
static_assert(mozilla::ArrayLength(kBase64URLDecodeTable) == 0x80);
bool
Base64URLCharToValue(char aChar, uint8_t* aValue) {
uint8_t index = static_cast<uint8_t>(aChar);
*aValue = kBase64URLDecodeTable[index & 0x7f];
return (*aValue != 255) && !(index & ~0x7f);
if (index >= mozilla::ArrayLength(kBase64URLDecodeTable)) {
*aValue = 255;
return false;
}
*aValue = kBase64URLDecodeTable[index];
return *aValue != 255;
}
} // namespace