Re: Re* [PATCH v7 1/1] sideband: highlight keywords in remote sideband output

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Aug 18, 2018, 06:09 UTC
Message-ID: <20180818060911.GC241538@aiede.svl.corp.google.com>
In-Reply-To: <xmqq8t54bzo4.fsf_-_@gitster-ct.c.googlers.com>

(-cc: my @google.com email) Hi,

Junio C Hamano wrote:

Show 15 quoted lines

> Subject: sideband: do not read beyond the end of input
>
> The caller of maybe_colorize_sideband() gives a counted buffer
> <src,n>, but the callee checked *src as if it were a NUL terminated
> buffer.  If src[] had all isspace() bytes in it, we would have made
> n negative, and then (1) called number of strncasecmp() to see if
> the remaining bytes in src[] matched keywords, reading beyond the
> end of the array, and/or (2) called strbuf_add() with negative
> count, most likely triggering the "you want to use way too much
> memory" error due to unsigned integer overflow.
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>  sideband.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

This indeed avoids the "you want to use way too much memory" error when I apply it.

> --- a/sideband.c
> +++ b/sideband.c
> @@ -75,7 +75,7 @@ static void maybe_colorize_sideband(struct strbuf *dest, const char *src, int n)

Not about this patch: should the 'n' parameter be a size_t instead of an int? It doesn't matter in practice (since the caller has an int, it can never be more than INT_MAX) but it might make the intent clearer.

Based on inspecting the caller, using an int seems fine.

Show 5 quoted lines

>  		return;
>  	}
>  
> -	while (isspace(*src)) {
> +	while (0 < n && isspace(*src)) {

Yes, we need to check 'n && isspace(*src)' to avoid overflowing the buffer if it consists entirely of spaces.

Show 10 quoted lines

>  		strbuf_addch(dest, *src);
>  		src++;
>  		n--;
> @@ -84,6 +84,9 @@ static void maybe_colorize_sideband(struct strbuf *dest, const char *src, int n)
>  	for (i = 0; i < ARRAY_SIZE(keywords); i++) {
>  		struct keyword_entry *p = keywords + i;
>  		int len = strlen(p->keyword);
> +
> +		if (n <= len)
> +			continue;

Using <= instead of < since we look at the character after the word as well. Good.

Show 7 quoted lines

>  		/*
>  		 * Match case insensitively, so we colorize output from existing
>  		 * servers regardless of the case that they use for their
> 		 * messages. We only highlight the word precisely, so
> 		 * "successful" stays uncolored.
> 		 */
> 		if (!strncasecmp(p->keyword, src, len) && !isalnum(src[len])) {

Not about this patch: should this check "&& src[len] == ':'" instead, as discussed upthread?

Show 7 quoted lines

> @@ -100,8 +103,8 @@ static void maybe_colorize_sideband(struct strbuf *dest, const char *src, int n)
>  		}
>  	}
>  
> -	strbuf_add(dest, src, n);
> +	if (0 < n)
> +		strbuf_add(dest, src, n);

This check seems unnecessary. strbuf_add can cope fine with !n. Should we put

	assert(n >= 0);

or even

	if (n < 0)
		BUG();

instead, since the earlier part of the fix guarantees that n >= 0?

Thanks for the careful work.  With or without such a change,
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>

Thanks.