Re: [PATCH] Continued cleanup of open_cred_file and fixed a potential security risk. The parsing for values has been moved to its own function and is a bit cleaner. Temporary buffers are zeroed out before being freed to ensure passwords/credentials aren't left in released memory.

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Sat, 24 Apr 2010 19:21:08 -0400
Scott Lovenberg <[email protected]> wrote:

Maybe try not to put all of the description on the subject line. You
can use multiple lines and it makes it a little tougher to import the
patch.

> Signed-off-by: Scott Lovenberg <[email protected]>
> ---
>  mount.cifs.c |  141 ++++++++++++++++++++++++++++++++++------------------------
>  1 files changed, 83 insertions(+), 58 deletions(-)
> 
> diff --git a/mount.cifs.c b/mount.cifs.c
> index 97dae82..09d6351 100644
> --- a/mount.cifs.c
> +++ b/mount.cifs.c
> @@ -121,6 +121,14 @@
>   */
>  #define CIFS_SETUID_FLAGS (MS_NOSUID|MS_NODEV)
>  
> +/*
> + * Values for parsing a credentials file.
> + */
> +#define CRED_UNPARSEABLE 0
> +#define CRED_USER 1
> +#define CRED_PASS 2
> +#define CRED_DOM 4
> +
>  /* struct for holding parsed mount info for use by privleged process */
>  struct parsed_mount_info {
>  	unsigned long flags;
> @@ -511,20 +519,43 @@ toggle_dac_capability(int writable, int enable)
>  #endif /* HAVE_LIBCAP */
>  #endif /* HAVE_LIBCAP_NG */
>  
> -/*
> - * Null terminate string at first '\n'
> - */
> -static void null_terminate_endl(char* source)
> +static void null_terminate_endl(char *source)
>  {
> -	char* newline = strchr(source, '\n');
> +	char *newline = strchr(source, '\n');
>  	if (newline)
>  		*newline = '\0';
>  }
>  
> -
> +/*
> + * Parse a line from the credentials file.  Changes target to first
> + * character after '=' on 'line' and returns the value type of the line
> + * Returns CRED_UNPARSEABLE on failure or if either parameter is NULL.
> + */
> +static int parse_cred_line(char *line, char **target)
> +{
> +	if (line == NULL || target == NULL)
> +		goto parsing_err;
> +
> +	/* position target at first char of value */
> +	*target = strchr(line, '=');
> +	if (!target)
	^^^^^^^^^^^^
Should be:
	if (!*target)

...right?

> +		goto parsing_err;
> +	*target += 1;
> +
> +	/* tell the caller which value target points to */
> +	if (strncasecmp("user", line, 4) == 0)
> +		return CRED_USER;
> +	if (strncasecmp("pass", line, 4) == 0)
> +		return CRED_PASS;
> +	if (strncasecmp("dom", line, 3) == 0)
> +		return CRED_DOM;
> +
> +	parsing_err:
> +		return CRED_UNPARSEABLE;
> +}
>  
>  static int open_cred_file(char *file_name,
> -			  struct parsed_mount_info *parsed_info)
> +			struct parsed_mount_info *parsed_info)
>  {
>  	char *line_buf;
>  	char *temp_val;
> @@ -535,30 +566,29 @@ static int open_cred_file(char *file_name,
>  
>  	i = toggle_dac_capability(0, 1);
>  	if (i)
> -		return i;
> -
> +		goto return_i;
> +	
>  	i = access(file_name, R_OK);
>  	if (i) {
>  		toggle_dac_capability(0, 0);
> -		return i;
> +		goto return_i;
>  	}
>  
>  	fs = fopen(file_name, "r");
>  	if (fs == NULL) {
>  		toggle_dac_capability(0, 0);
> -		return errno;
> +		i = errno;
> +		goto return_i;
>  	}
>  
>  	i = toggle_dac_capability(0, 0);
> -	if (i) {
> -		fclose(fs);
> -		return i;
> -	}
> -
> -	line_buf = (char *)malloc(line_buf_size);
> +	if(i)
> +		goto return_i;
> +	
> +	line_buf = (char*)malloc(line_buf_size);
>  	if (line_buf == NULL) {
> -		fclose(fs);
> -		return EX_SYSERR;
> +		i = EX_SYSERR;
> +		goto return_i;
>  	}
>  
>  	/* parse line from credentials file */
> @@ -570,47 +600,42 @@ static int open_cred_file(char *file_name,
>  		}
>  		null_terminate_endl(line_buf);
>  
> -		/* parse user */
> -		if (strncasecmp("user", line_buf + i, 4) == 0) {
> -			temp_val = strchr(line_buf + i, '=');
> -			if (temp_val) {
> -				/* go past equals sign */
> -				temp_val++;
> -				parsed_info->got_user = 1;
> -				strlcpy(parsed_info->username, temp_val,
> -					sizeof(parsed_info->username));
> -			}
> -		} 
> -
> -		/* parse password */
> -		else if (strncasecmp("pass", line_buf + i, 4) == 0) {
> -			temp_val = strchr(line_buf + i, '=');
> -			if (!temp_val)
> -				continue;
> -			++temp_val;
> -			i = set_password(parsed_info, temp_val);
> -			if (i)
> -				return i;
> -		} 
> -
> -		/* parse domain */
> -		else if (strncasecmp("dom", line_buf + i, 3) == 0) {
> -			temp_val = strchr(line_buf + i, '=');
> -			if (temp_val) {
> -				/* go past equals sign */
> -				temp_val++;
> -				if (parsed_info->verboseflag)
> -					fprintf(stderr, "\nDomain %s\n",
> -						temp_val);
> -				strlcpy(parsed_info->domain, temp_val,
> -					sizeof(parsed_info->domain));
> -			}
> +		/* parse next token */
> +		switch(parse_cred_line(line_buf + i, &temp_val)) {
> +		case CRED_USER:
> +			parse_username(temp_val, parsed_info);

I think you should check the return value from parse_username here too.

> +			break;
> +		case CRED_PASS:
> +			if ((i = set_password(parsed_info, temp_val)))
> +				goto return_i;
> +			break;
> +		case CRED_DOM:
> +			if (parsed_info->verboseflag)
> +				fprintf(stderr, "\nDomain %s\n",
> +					temp_val);
> +			strlcpy(parsed_info->domain, temp_val,
> +				sizeof(parsed_info->domain));
> +			break;
> +		case CRED_UNPARSEABLE:
> +			if (parsed_info->verboseflag)
> +				fprintf(stderr,
> +					"Credential formatted incorrectly: %s",
> +					temp_val);
> +			break;
>  		}
> -
>  	}
> -	fclose(fs);
> -	SAFE_FREE(line_buf);
> -	return 0;
> +
> +	i = 0;
> +	/* jump point for errors */
> +	return_i:

	^^^^^^^^
Minor nit: typically labels are flush to the left, and the code below
shouldn't be indented as much.

> +		if (fs != NULL)
> +			fclose(fs);
> +
> +		/* make sure passwords are scrubbed from memory */
> +		if (line_buf != NULL)
> +			memset(line_buf, 0, line_buf_size);
> +		SAFE_FREE(line_buf);
> +		return i;
>  }
>  
>  static int

There's also some trailing whitespace and other formatting errors that
checkpatch complained about, and the patch didn't apply cleanly to the
head git commit. I cleaned up most of these problems and will send a
revised patch in a bit.

- -- 
Jeff Layton <[email protected]>
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.14 (GNU/Linux)

iEYEARECAAYFAkvURfsACgkQyP0gxQMdzIAcNgCgkfVOVnYMIeLgxjnmDlFjURTV
sCQAn2gmgmkJ80WDfc/UDwyY5uhqNbsJ
=iFIZ
-----END PGP SIGNATURE-----