Re: [PATCH] daemon: detect and reject too-long paths

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> When we are checking the path via path_ok(), we use some
> fixed PATH_MAX buffers. We write into them via snprintf(),
> so there's no possibility of overflow, but it does mean we
> may silently truncate the path, leading to potentially
> confusing errors when the partial path does not exist.
>
> We're better off to reject the path explicitly.
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---

Sounds sensible.

> Another option would be to switch to strbufs here. That potentially
> introduces cases where a client can convince us to just keep allocating
> memory, but I don't think so in practice; the paths and interpolated
> data items all have to come in 64K pkt-lines, which places a hard
> limit. This is a much more minimal change, though, and I don't hear
> anybody complaining about the inability to use large paths.

The alternative version did not look bad, either; in fact, the end
result may even be conceptually simpler.

But I agree that this one with the same hard-limit we always had is
a much more minimal change and is sufficient.

Thanks.

>  daemon.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/daemon.c b/daemon.c
> index 425aad0507..ff0fa583b0 100644
> --- a/daemon.c
> +++ b/daemon.c
> @@ -160,6 +160,7 @@ static const char *path_ok(const char *directory, struct hostinfo *hi)
>  {
>  	static char rpath[PATH_MAX];
>  	static char interp_path[PATH_MAX];
> +	size_t rlen;
>  	const char *path;
>  	const char *dir;
>  
> @@ -187,8 +188,12 @@ static const char *path_ok(const char *directory, struct hostinfo *hi)
>  			namlen = slash - dir;
>  			restlen -= namlen;
>  			loginfo("userpath <%s>, request <%s>, namlen %d, restlen %d, slash <%s>", user_path, dir, namlen, restlen, slash);
> -			snprintf(rpath, PATH_MAX, "%.*s/%s%.*s",
> -				 namlen, dir, user_path, restlen, slash);
> +			rlen = snprintf(rpath, sizeof(rpath), "%.*s/%s%.*s",
> +					namlen, dir, user_path, restlen, slash);
> +			if (rlen >= sizeof(rpath)) {
> +				logerror("user-path too large: %s", rpath);
> +				return NULL;
> +			}
>  			dir = rpath;
>  		}
>  	}
> @@ -207,7 +212,15 @@ static const char *path_ok(const char *directory, struct hostinfo *hi)
>  
>  		strbuf_expand(&expanded_path, interpolated_path,
>  			      expand_path, &context);
> -		strlcpy(interp_path, expanded_path.buf, PATH_MAX);
> +
> +		rlen = strlcpy(interp_path, expanded_path.buf,
> +			       sizeof(interp_path));
> +		if (rlen >= sizeof(interp_path)) {
> +			logerror("interpolated path too large: %s",
> +				 interp_path);
> +			return NULL;
> +		}
> +
>  		strbuf_release(&expanded_path);
>  		loginfo("Interpolated dir '%s'", interp_path);
>  
> @@ -219,7 +232,11 @@ static const char *path_ok(const char *directory, struct hostinfo *hi)
>  			logerror("'%s': Non-absolute path denied (base-path active)", dir);
>  			return NULL;
>  		}
> -		snprintf(rpath, PATH_MAX, "%s%s", base_path, dir);
> +		rlen = snprintf(rpath, sizeof(rpath), "%s%s", base_path, dir);
> +		if (rlen >= sizeof(rpath)) {
> +			logerror("base-path too large: %s", rpath);
> +			return NULL;
> +		}
>  		dir = rpath;
>  	}