/* Provenance: openssl/openssl ssl3_read_n (fixed).
 * repo: openssl/openssl
 * commit: 2d05959073c4bf8803401668b9df85931a08e020
 * parent: b3f0eb0a295f58f16ba43ba99dad70d4ee5c437d
 * commit_url: https://github.com/openssl/openssl/commit/2d05959073c4bf8803401668b9df85931a08e020
 * cve: CVE-2024-4741
 * license: Apache-2.0
 * function: ssl3_read_n
 * relpath: ssl/record/rec_layer_s3.c
 */

int ssl3_read_n(SSL *s, size_t n, size_t max, int extend, int clearold,
                size_t *readbytes)
{
    /*
     * If extend == 0, obtain new n-byte packet; if extend == 1, increase
     * packet by another n bytes. The packet will be in the sub-array of
     * s->rlayer.rbuf.buf specified by s->rlayer.packet and
     * s->rlayer.packet_length. (If s->rlayer.read_ahead is set, 'max' bytes may
     * be stored in rbuf [plus s->rlayer.packet_length bytes if extend == 1].)
     * if clearold == 1, move the packet to the start of the buffer; if
     * clearold == 0 then leave any old packets where they were
     */
    size_t len, left, align = 0;
    unsigned char *pkt;
    SSL3_BUFFER *rb;

    if (n == 0)
        return 0;

    rb = &s->rlayer.rbuf;
    if (rb->buf == NULL)
        if (!ssl3_setup_read_buffer(s)) {
            /* SSLfatal() already called */
            return -1;
        }

    left = rb->left;
#if defined(SSL3_ALIGN_PAYLOAD) && SSL3_ALIGN_PAYLOAD!=0
    align = (size_t)rb->buf + SSL3_RT_HEADER_LENGTH;
    align = SSL3_ALIGN_PAYLOAD - 1 - ((align - 1) % SSL3_ALIGN_PAYLOAD);
#endif

    if (!extend) {
        /* start with empty packet ... */
        if (left == 0)
            rb->offset = align;

        s->rlayer.packet = rb->buf + rb->offset;
        s->rlayer.packet_length = 0;
        /* ... now we can act as if 'extend' was set */
    }

    if (!ossl_assert(s->rlayer.packet != NULL)) {
        /* does not happen */
        SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR);
        return -1;
    }

    len = s->rlayer.packet_length;
    pkt = rb->buf + align;
    /*
     * Move any available bytes to front of buffer: 'len' bytes already
     * pointed to by 'packet', 'left' extra ones at the end
     */
    if (s->rlayer.packet != pkt && clearold == 1) {
        memmove(pkt, s->rlayer.packet, len + left);
        s->rlayer.packet = pkt;
        rb->offset = len + align;
    }

    /*
     * For DTLS/UDP reads should not span multiple packets because the read
     * operation returns the whole packet at once (as long as it fits into
     * the buffer).
     */
    if (SSL_IS_DTLS(s)) {
        if (left == 0 && extend)
            return 0;
        if (left > 0 && n > left)
            n = left;
    }

    /* if there is enough in the buffer from a previous read, take some */
    if (left >= n) {
        s->rlayer.packet_length += n;
        rb->left = left - n;
        rb->offset += n;
        *readbytes = n;
        return 1;
    }

    /* else we need to read more data */

    if (n > rb->len - rb->offset) {
        /* does not happen */
        SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR);
        return -1;
    }

    /*
     * Ktls always reads full records.
     * Also, we always act like read_ahead is set for DTLS.
     */
    if (!BIO_get_ktls_recv(s->rbio) && !s->rlayer.read_ahead
        && !SSL_IS_DTLS(s)) {
        /* ignore max parameter */
        max = n;
    } else {
        if (max < n)
            max = n;
        if (max > rb->len - rb->offset)
            max = rb->len - rb->offset;
    }

    while (left < n) {
        size_t bioread = 0;
        int ret;

        /*
         * Now we have len+left bytes at the front of s->s3.rbuf.buf and
         * need to read in more until we have len+n (up to len+max if
         * possible)
         */

        clear_sys_error();
        if (s->rbio != NULL) {
            s->rwstate = SSL_READING;
            ret = BIO_read(s->rbio, pkt + len + left, max - left);
            if (ret >= 0)
                bioread = ret;
            if (ret <= 0
                    && !BIO_should_retry(s->rbio)
                    && BIO_eof(s->rbio)) {
                if (s->options & SSL_OP_IGNORE_UNEXPECTED_EOF) {
                    SSL_set_shutdown(s, SSL_RECEIVED_SHUTDOWN);
                    s->s3.warn_alert = SSL_AD_CLOSE_NOTIFY;
                } else {
                    /*
                     * This reason code is part of the API and may be used by
                     * applications for control flow decisions.
                     */
                    SSLfatal(s, SSL_AD_DECODE_ERROR,
                             SSL_R_UNEXPECTED_EOF_WHILE_READING);
                }
            }
        } else {
            SSLfatal(s, SSL_AD_INTERNAL_ERROR, SSL_R_READ_BIO_NOT_SET);
            ret = -1;
        }

        if (ret <= 0) {
            rb->left = left;
            if (s->mode & SSL_MODE_RELEASE_BUFFERS && !SSL_IS_DTLS(s))
                if (len + left == 0)
                    ssl3_release_read_buffer(s);
            return ret;
        }
        left += bioread;
        /*
         * reads should *never* span multiple packets for DTLS because the
         * underlying transport protocol is message oriented as opposed to
         * byte oriented as in the TLS case.
         */
        if (SSL_IS_DTLS(s)) {
            if (n > left)
                n = left;       /* makes the while condition false */
        }
    }

    /* done reading, now the book-keeping */
    rb->offset += n;
    rb->left = left - n;
    s->rlayer.packet_length += n;
    s->rwstate = SSL_NOTHING;
    *readbytes = n;
    return 1;
}