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base64: Added basic validation to base64 input string when decoding

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A base64 string should be a multiple of 4 characters in length, not
contain any more than 2 padding characters and only contain padding
characters at the end of string. For example: Y3VybA==

Strings such as the following are considered invalid:

Y=   - Invalid length
Y==  - Invalid length
Y=== - More than two padding characters
Y=x= - Padding character contained within string
This commit is contained in:
Steve Holme
2013-10-30 07:31:22 +00:00
parent 7d1eb66cd7
commit e17c1b25bc
2 changed files with 33 additions and 6 deletions
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19
lib/base64.c
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@@ -82,6 +82,7 @@ static void decodeQuantum(unsigned char *dest, const char *src)
CURLcode Curl_base64_decode(const char *src,
unsigned char **outptr, size_t *outlen)
{
size_t srcLen = 0;
size_t length = 0;
size_t equalsTerm = 0;
size_t i;
@@ -92,21 +93,31 @@ CURLcode Curl_base64_decode(const char *src,
*outptr = NULL;
*outlen = 0;
srcLen = strlen(src);
/* Check the length of the input string is valid */
if(!srcLen || srcLen % 4)
return CURLE_BAD_CONTENT_ENCODING;
/* Find the position of any = padding characters */
while((src[length] != '=') && src[length])
length++;
/* A maximum of two = padding characters is allowed */
if(src[length] == '=') {
equalsTerm++;
if(src[length+equalsTerm] == '=')
equalsTerm++;
}
/* Check the = padding characters weren't part way through the input */
if(length + equalsTerm != srcLen)
return CURLE_BAD_CONTENT_ENCODING;
/* Calculate the number of quantums */
numQuantums = (length + equalsTerm) / 4;
/* Don't allocate a buffer if the decoded length is 0 */
if(numQuantums == 0)
return CURLE_OK;
/* Calculate the size of the decoded string */
rawlen = (numQuantums * 3) - equalsTerm;
/* The buffer must be large enough to make room for the last quantum