Commit 0ceac0d0ce592c8c26575a12d47f5371e69aff79
2019-01-23T14:45:19
mbedtls: fix potential size overflow when reading or writing data The mbedtls library uses a callback mechanism to allow downstream users to plug in their own receive and send functions. We implement `bio_read` and `bio_write` functions, which simply wrap the `git_stream_read` and `git_stream_write` functions, respectively. The problem arises due to the return value of the callback functions: mbedtls expects us to return an `int` containing the actual number of bytes that were read or written. But this is in fact completely misdesigned, as callers are allowed to pass in a buffer with length `SIZE_MAX`. We thus may be unable to represent the number of bytes written via the return value. Fix this by only ever reading or writing at most `INT_MAX` bytes.
diff --git a/src/streams/mbedtls.c b/src/streams/mbedtls.c
index 2ade83c..cbe2f68 100644
--- a/src/streams/mbedtls.c
+++ b/src/streams/mbedtls.c
@@ -169,13 +169,13 @@ cleanup:
static int bio_read(void *b, unsigned char *buf, size_t len)
{
git_stream *io = (git_stream *) b;
- return (int) git_stream_read(io, buf, len);
+ return (int) git_stream_read(io, buf, min(len, INT_MAX));
}
static int bio_write(void *b, const unsigned char *buf, size_t len)
{
git_stream *io = (git_stream *) b;
- return (int) git_stream_write(io, (const char *)buf, len, 0);
+ return (int) git_stream_write(io, (const char *)buf, min(len, INT_MAX), 0);
}
static int ssl_set_error(mbedtls_ssl_context *ssl, int error)
@@ -308,6 +308,13 @@ static ssize_t mbedtls_stream_write(git_stream *stream, const char *data, size_t
GIT_UNUSED(flags);
+ /*
+ * `mbedtls_ssl_write` can only represent INT_MAX bytes
+ * written via its return value. We thus need to clamp
+ * the maximum number of bytes written.
+ */
+ len = min(len, INT_MAX);
+
if ((written = mbedtls_ssl_write(st->ssl, (const unsigned char *)data, len)) <= 0)
return ssl_set_error(st->ssl, written);