Correct calculation of base64 encode buffer length.

In the previous formulation, it would first multiple then divide. It would then
promote to unsigned int. The formula would overflow for large len. For example,
needed = 2 when len == INT_MAX. In the revised formulation, it is promoted,
divided, then multiplied. The revised calculation avoids the overflow and
computes needed correctly over len in {0, 1, ..., INT_MAX}.  For len == INT_MAX,
needed is correctly computed as 2863311533.

Signed-off-by: Tom Carroll <incentivedesign@gmail.com>

diff --git a/http-auth.c b/http-auth.c
index 8c3270b77769fa1c38aa41efd3b71aa076ba56d4..d6e2c6b7982d605622a1e464af0b2695a5e72a37 100644 (file)
--- a/http-auth.c
+++ b/http-auth.c
@@ -119,7 +119,7 @@ void buf_append_base64(struct oc_text_buf *buf, const void *bytes, int len,
        if (!buf || buf->error)
                return;
 
-       unsigned int needed = (4 * (len + 2) / 3) + 1;
+       unsigned int needed = ((len + 2u) / 3) * 4 + 1;
        if (line_len)
                needed += needed / line_len;