Re: [PATCH v4] libselinux: correct error path to always try text

[Stephen Smalley <sds@tycho.nsa.gov>]

On 09/16/2016 02:32 PM, william.c.roberts@intel.com wrote:
> From: William Roberts <william.c.roberts@intel.com>
> 
> patch 5e15a52aaa cleans up the process_file() routine,
> but introduced a bug. If the binary file cannot be
> opened, always attempt to fall back to the textual file,
> this was not occurring.
> 
> The logic should be:
> 1. Open the newest file between base path + suffix and
>    base_path + suffix + ".bin"
> 2. If anything fails, attempt to load the oldest file.
> 
> The result, with a concrete example, would be:
> If file_contexts is the newest file, and it cannot be
> processed, the code will fall back to file_contexts.bin
> and vice versa.
> 
> Signed-off-by: William Roberts <william.c.roberts@intel.com>
> ---
>  libselinux/src/label_file.c | 48 +++++++++++++++++++++++++++++++--------------
>  1 file changed, 33 insertions(+), 15 deletions(-)
> 
> diff --git a/libselinux/src/label_file.c b/libselinux/src/label_file.c
> index 9faecdb..4f3700c 100644
> --- a/libselinux/src/label_file.c
> +++ b/libselinux/src/label_file.c
> @@ -447,7 +447,7 @@ static bool fcontext_is_binary(FILE *fp)
>  #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
>  
>  static FILE *open_file(const char *path, const char *suffix,
> -		       char *save_path, size_t len, struct stat *sb)
> +	       char *save_path, size_t len, struct stat *sb, bool open_oldest)
>  {
>  	unsigned int i;
>  	int rc;
> @@ -493,9 +493,17 @@ static FILE *open_file(const char *path, const char *suffix,
>  		 * includes equality. This provides a precedence on
>  		 * secondary suffixes even when the timestamp is the
>  		 * same. Ie choose file_contexts.bin over file_contexts
> -		 * even if the time stamp is the same.
> +		 * even if the time stamp is the same. Invert this logic
> +		 * on open_oldest set to true. The idea is that if the
> +		 * newest file failed to process, we can attempt to
> +		 * process the oldest. The logic here is subtle and depends
> +		 * on the array ordering in fdetails for the case when time
> +		 * stamps are the same.
>  		 */
> -		if (fdetails[i].sb.st_mtime >= found->sb.st_mtime) {
> +		if ((!open_oldest
> +			&& fdetails[i].sb.st_mtime >= found->sb.st_mtime)
> +			|| (open_oldest
> +			&& fdetails[i].sb.st_mtime < found->sb.st_mtime)) {

This can be simplified using ^ (xor).

>  			found = &fdetails[i];
>  			strcpy(save_path, path);
>  		}
> @@ -515,24 +523,34 @@ static int process_file(const char *path, const char *suffix,
>  			  const char *prefix, struct selabel_digest *digest)
>  {
>  	int rc;
> +	unsigned int i;
>  	struct stat sb;
>  	FILE *fp = NULL;
>  	char found_path[PATH_MAX];
>  
> -	fp = open_file(path, suffix, found_path, sizeof(found_path), &sb);
> -	if (fp == NULL)
> -		return -1;
> +	/*
> +	 * first path open the newest modified file, if it fails, the second

pass, opens

> +	 * pass opens the oldest file. If both passes fail, its a fatal error.

it is

> +	 */
> +	for (i = 0; i < 2; i++) {
> +		fp = open_file(path, suffix, found_path, sizeof(found_path),
> +			&sb, i > 0);
> +		if (fp == NULL)
> +			return -1;
>  
> -	rc = fcontext_is_binary(fp) ?
> -			load_mmap(fp, sb.st_size, rec, found_path) :
> -			process_text_file(fp, prefix, rec, found_path);
> -	if (rc < 0)
> -		goto out;
> +		rc = fcontext_is_binary(fp) ?
> +				load_mmap(fp, sb.st_size, rec, found_path) :
> +				process_text_file(fp, prefix, rec, found_path);
> +		if (!rc)
> +			rc = digest_add_specfile(digest, fp, NULL, sb.st_size,
> +				found_path);
>  
> -	rc = digest_add_specfile(digest, fp, NULL, sb.st_size, found_path);
> -out:
> -	fclose(fp);
> -	return rc;
> +		fclose(fp);
> +
> +		if (!rc)
> +			return 0;
> +	}
> +	return -1;
>  }
>  
>  static void closef(struct selabel_handle *rec);
>