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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
View File

@ -82,6 +82,7 @@ static void decodeQuantum(unsigned char *dest, const char *src)
CURLcode Curl_base64_decode(const char *src, CURLcode Curl_base64_decode(const char *src,
unsigned char **outptr, size_t *outlen) unsigned char **outptr, size_t *outlen)
{ {
size_t srcLen = 0;
size_t length = 0; size_t length = 0;
size_t equalsTerm = 0; size_t equalsTerm = 0;
size_t i; size_t i;
@ -92,21 +93,31 @@ CURLcode Curl_base64_decode(const char *src,
*outptr = NULL; *outptr = NULL;
*outlen = 0; *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]) while((src[length] != '=') && src[length])
length++; length++;
/* A maximum of two = padding characters is allowed */ /* A maximum of two = padding characters is allowed */
if(src[length] == '=') { if(src[length] == '=') {
equalsTerm++; equalsTerm++;
if(src[length+equalsTerm] == '=') if(src[length+equalsTerm] == '=')
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; numQuantums = (length + equalsTerm) / 4;
/* Don't allocate a buffer if the decoded length is 0 */ /* Calculate the size of the decoded string */
if(numQuantums == 0)
return CURLE_OK;
rawlen = (numQuantums * 3) - equalsTerm; rawlen = (numQuantums * 3) - equalsTerm;
/* The buffer must be large enough to make room for the last quantum /* The buffer must be large enough to make room for the last quantum

20
tests/unit/unit1302.c
View File

@ -104,11 +104,27 @@ fail_unless(size == 1, "size should be 1");
verify_memory(decoded, "i", 2); verify_memory(decoded, "i", 2);
Curl_safefree(decoded); Curl_safefree(decoded);
/* this is an illegal input */ /* This is illegal input as the data is too short */
size = 1; /* not zero */ size = 1; /* not zero */
decoded = &anychar; /* not NULL */ decoded = &anychar; /* not NULL */
rc = Curl_base64_decode("aQ", &decoded, &size); rc = Curl_base64_decode("aQ", &decoded, &size);
/* return code indiferent, but output shall be as follows */ fail_unless(rc == CURLE_BAD_CONTENT_ENCODING, "return code should be CURLE_BAD_CONTENT_ENCODING");
fail_unless(size == 0, "size should be 0");
fail_if(decoded, "returned pointer should be NULL");
/* This is illegal input as it contains three padding characters */
size = 1; /* not zero */
decoded = &anychar; /* not NULL */
rc = Curl_base64_decode("a===", &decoded, &size);
fail_unless(rc == CURLE_BAD_CONTENT_ENCODING, "return code should be CURLE_BAD_CONTENT_ENCODING");
fail_unless(size == 0, "size should be 0");
fail_if(decoded, "returned pointer should be NULL");
/* This is illegal input as it contains a padding character mid input */
size = 1; /* not zero */
decoded = &anychar; /* not NULL */
rc = Curl_base64_decode("a=Q=", &decoded, &size);
fail_unless(rc == CURLE_BAD_CONTENT_ENCODING, "return code should be CURLE_BAD_CONTENT_ENCODING");
fail_unless(size == 0, "size should be 0"); fail_unless(size == 0, "size should be 0");
fail_if(decoded, "returned pointer should be NULL"); fail_if(decoded, "returned pointer should be NULL");