[gnutls-devel] GnuTLS | gnutls_buffer_append_data: avoid use-after-free in the callers (!1399)

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Tue Mar 9 18:27:30 CET 2021

Daiki Ueno commented on a discussion on lib/ext/key_share.c: https://gitlab.com/gnutls/gnutls/-/merge_requests/1399#note_525432181

>  		if (!have_creds_for_tls13(session))
>  			return 0;
> -		/* write the total length later */
> -		lengthp = &extdata->data[extdata->length];

Yes; there are several calls to `_gnutls_buffer_append*` between here and the place where the length is actually assigned, if `realloc` (called underneath) allocates a new memory, `lengthp` can be invalid.

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