commit 3c35c0d441cc25f750524056113970a376d8432c Author: Nick Mathewson nickm@torproject.org Date: Fri Dec 14 13:07:55 2018 -0500

Add a function to provide an upper bound on base64 decoded length --- src/lib/encoding/binascii.c | 12 ++++++++++++ src/lib/encoding/binascii.h | 1 + src/test/test_util_format.c | 4 +++- 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/lib/encoding/binascii.c b/src/lib/encoding/binascii.c index e9140d943..067db075a 100644 --- a/src/lib/encoding/binascii.c +++ b/src/lib/encoding/binascii.c @@ -179,6 +179,18 @@ base64_encode_size(size_t srclen, int flags) return enclen; }

+/** Return an upper bound on the number of bytes that might be needed to hold + * the data from decoding the base64 string <b>srclen</b>. This is only an + * upper bound, since some part of the base64 string might be padding or + * space. */ +size_t +base64_decode_maxsize(size_t srclen) +{ + tor_assert(srclen < INT_MAX / 3); + + return CEIL_DIV(srclen * 3, 4); +} + /** Internal table mapping 6 bit values to the Base64 alphabet. */ static const char base64_encode_table[64] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', diff --git a/src/lib/encoding/binascii.h b/src/lib/encoding/binascii.h index 23cbaa707..c71ba65df 100644 --- a/src/lib/encoding/binascii.h +++ b/src/lib/encoding/binascii.h @@ -42,6 +42,7 @@ const char *hex_str(const char *from, size_t fromlen);

#define BASE64_ENCODE_MULTILINE 1 size_t base64_encode_size(size_t srclen, int flags); +size_t base64_decode_maxsize(size_t srclen); int base64_encode(char *dest, size_t destlen, const char *src, size_t srclen, int flags); int base64_decode(char *dest, size_t destlen, const char *src, size_t srclen); diff --git a/src/test/test_util_format.c b/src/test/test_util_format.c index 85d8a8e62..fd57125b8 100644 --- a/src/test/test_util_format.c +++ b/src/test/test_util_format.c @@ -392,10 +392,13 @@ test_util_format_encoded_size(void *arg)

base64_encode(outbuf, sizeof(outbuf), (char *)inbuf, i, 0); tt_int_op(strlen(outbuf), OP_EQ, base64_encode_size(i, 0)); + tt_int_op(i, OP_LE, base64_decode_maxsize(strlen(outbuf))); + base64_encode(outbuf, sizeof(outbuf), (char *)inbuf, i, BASE64_ENCODE_MULTILINE); tt_int_op(strlen(outbuf), OP_EQ, base64_encode_size(i, BASE64_ENCODE_MULTILINE)); + tt_int_op(i, OP_LE, base64_decode_maxsize(strlen(outbuf))); }

done: @@ -417,4 +420,3 @@ struct testcase_t util_format_tests[] = { { "encoded_size", test_util_format_encoded_size, 0, NULL, NULL }, END_OF_TESTCASES }; -