[lttng-dev] [lttng-tools PATCH 3/4] Correct the behavior of the utils_expand_path function

[Mathieu Desnoyers]

Here are comments about the patch, even though it has been merged.

----- Original Message -----
> From: "Raphaël Beamonte" <raphael.beamonte at gmail.com>
> To: dgoulet at efficios.com
> Cc: "Raphaël Beamonte" <raphael.beamonte at gmail.com>, lttng-dev at lists.lttng.org
> Sent: Wednesday, November 13, 2013 12:34:37 AM
> Subject: [lttng-dev] [lttng-tools PATCH 3/4] Correct the behavior of the	utils_expand_path function
> 
> Even if the utils_expand_path function was intended to allow to
> use unexistent directory paths, it was in fact only working for
> some kind of arguments. Paths like "foo", "bar/" or "bar/foo"
> when the "bar" directory does not exist wasn't working. This
> patch introduce a new way to expand paths in this function that
> also works properly for these kind of arguments.
> 
> Signed-off-by: Raphaël Beamonte <raphael.beamonte at gmail.com>
> ---
>  src/common/utils.c |   86
>  ++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 64 insertions(+), 22 deletions(-)
> 
> diff --git a/src/common/utils.c b/src/common/utils.c
> index 4ccf36a..6938a5a 100644
> --- a/src/common/utils.c
> +++ b/src/common/utils.c
> @@ -112,7 +112,7 @@ error:
>  LTTNG_HIDDEN
>  char *utils_expand_path(const char *path)
>  {
> -	const char *end_path = path;
> +	const char *end_path = NULL;
>  	char *next, *cut_path = NULL, *expanded_path = NULL;
>  
>  	/* Safety net */
> @@ -120,38 +120,80 @@ char *utils_expand_path(const char *path)
>  		goto error;
>  	}
>  
> -	/* Find last token delimited by '/' */
> -	while ((next = strpbrk(end_path + 1, "/"))) {
> -		end_path = next;
> -	}
> -
> -	/* Cut last token from original path */
> -	cut_path = strndup(path, end_path - path);
> -
> +	/* Allocate memory for the expanded path */
>  	expanded_path = zmalloc(PATH_MAX);
>  	if (expanded_path == NULL) {
>  		PERROR("zmalloc expand path");
>  		goto error;
>  	}
>  
> -	expanded_path = realpath((char *)cut_path, expanded_path);
> -	if (expanded_path == NULL) {
> -		switch (errno) {
> -		case ENOENT:
> -			ERR("%s: No such file or directory", cut_path);
> -			break;
> -		default:
> -			PERROR("realpath utils expand path");
> -			break;
> +	/* If given path is already absolute */
> +	if (*path == '/') {
> +		strncpy(expanded_path, path, PATH_MAX);
> +	/* Else, we have some work to do */
> +	} else {
> +		/* Pointer to the last char of the path */
> +		const char *last_char = path + strlen(path) - 1;
> +
> +		end_path = path;
> +
> +		/* Split part that will be resolved by realpath (relative path from

Comments should start with a:

 /*
  * Then start of comment...


> +		 * current directory using ./ or ../ only) and part that could not
> +		 * (directory names)
> +		 */
> +		while ((next = strpbrk(end_path, "/")) && (next != last_char)) {
> +			end_path = next + 1;
> +			if (strncmp(end_path, "./", 2) != 0 &&
> +					strncmp(end_path, "../", 3) != 0) {
> +				break;
> +			}
> +		}
> +
> +		/* If this is the end of the string, and we still can resolve it */
> +		if (strncmp(end_path, "..\0", 3) == 0 ||

There is no point in ending a "" with \0, it implicitly ends with a \0 already.

> +				strncmp(end_path, ".\0", 2) == 0) {

Same here.

> +			end_path += strlen(end_path);
> +		}
> +
> +		/* If the end part is the whole path, we are in the current dir */

Not necessarily. What happens in the unlikely case someone passes a path with simply "/" ?

> +		if (end_path == path) {
> +			cut_path = strdup(".");
> +		/* Else, cut the resolvable part from original path */
> +		} else {
> +			cut_path = strndup(path, end_path - path);
> +		}
> +
> +		/* Resolve the canonical path of the first part of the path */
> +		expanded_path = realpath((char *)cut_path, expanded_path);

So let's say we have:

"../blah/../blah"

so only "../" passed to realpath, or the entire "../blah/../blah" ? (let's suppose blah/ exists), right ?


> +		if (expanded_path == NULL) {
> +			switch (errno) {
> +			case ENOENT:
> +				ERR("%s: No such file or directory", cut_path);
> +				break;
> +			default:
> +				PERROR("realpath utils expand path");
> +				break;
> +			}
> +			goto error;
> +		}
> +
> +		/* Add end part to expanded path if not empty */
> +		if (*end_path != 0) {
> +			strncat(expanded_path, "/", PATH_MAX - strlen(expanded_path) - 1);
> +			strncat(expanded_path, end_path,
> +					PATH_MAX - strlen(expanded_path) - 1);
>  		}
> -		goto error;
>  	}
>  
> -	/* Add end part to expanded path */
> -	strncat(expanded_path, end_path, PATH_MAX - strlen(expanded_path) - 1);
> +	/* Resolve the internal './' and '../' strings */
> +	next = utils_resolve_relative(expanded_path);

In the "../blah/../blah" case, here the other ../ would be dealt with by utils_resolve_relative, is that it ?

Thanks,

Mathieu

> +	if (next == NULL) {
> +		goto error;
> +	}
>  
> +	free(expanded_path);
>  	free(cut_path);
> -	return expanded_path;
> +	return next;
>  
>  error:
>  	free(expanded_path);
> --
> 1.7.10.4
> 
> 
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> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com