ACK: [PATCH 5/5] lib: fwts_olog: avoid TOCTOU race on stat and fopen

[ivanhu]

On 2016年04月03日 01:52, Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
>
> stat'ing a file and then opening it is always a potential race condition
> as a user can change the file between the stat and the open. Only
> stat the file after it is open and also on the open check for the
> errno on a failed open and handle the file does not exist special
> case like the original stat did.
>
> Signed-off-by: Colin Ian King <colin.king at canonical.com>
> ---
>   src/lib/src/fwts_olog.c | 35 +++++++++++++++++++----------------
>   1 file changed, 19 insertions(+), 16 deletions(-)
>
> diff --git a/src/lib/src/fwts_olog.c b/src/lib/src/fwts_olog.c
> index 132efc4..12d693c 100644
> --- a/src/lib/src/fwts_olog.c
> +++ b/src/lib/src/fwts_olog.c
> @@ -28,6 +28,7 @@
>   #include <sys/stat.h>
>   #include <regex.h>
>   #include <fcntl.h>
> +#include <errno.h>
>
>   #include "fwts.h"
>
> @@ -57,20 +58,6 @@ fwts_list *fwts_olog_read(fwts_framework *fw)
>   	FILE* msglog_outfile_f;
>
>   	/*
> -	 * Check for the existance of the opal msglog and only if it exists
> -	 * dump it out.  This makes the use of the OLOG as a custom option
> -	 * and not just for PPC.  We don't use compiler flags since we want
> -	 * to run this as a custom job cross platform
> -	 */
> -	if (stat(msglog, &filestat)) {
> -		/*
> -		 * stat fails so not PPC with OPAL msglog and
> -		 * no -o OLOG sent
> -		 */
> -		return NULL;
> -	}
> -
> -	/*
>   	 * Special file handling to sequentially fread the sysfs msglog into
>   	 * a static buffer based on inodes in the stat.  The sysfs msglog has
>   	 * a 0 byte file size since it is a sysfs object.
> @@ -80,17 +67,33 @@ fwts_list *fwts_olog_read(fwts_framework *fw)
>   	 */
>   	if (!(msglog_f = fopen(msglog, "r"))) {
>   		/* open the sysfs msglog for read only */
> +		if (errno == ENOENT) {
> +			/*
> +			 * If file does not exist, treat as non-fatal
> +			 * for non PPC devices that don't have the
> +			 * arch specific sys file.
> +			 */
> +			return NULL;
> +		}
>   		goto olog_common_exit;
>   	}
>
> +	if (fstat(fileno(msglog_f), &filestat)) {
> +		/*
> +		 * stat fails so not PPC with OPAL msglog and
> +		 * no -o OLOG sent
> +		 */
> +		fclose(msglog_f);
> +		return NULL;
> +	}
> +
>   	if ((len = filestat.st_blksize) < 1) {
>   		/* if any size at all continue */
>   		goto olog_cleanup_msglog;
>   	}
>
> -	if ((buffer = calloc(1, len + 1)) == NULL) {
> +	if ((buffer = calloc(1, len + 1)) == NULL)
>   		goto olog_cleanup_msglog;
> -	}
>
>   	if (!(msglog_outfile_f = fopen(msglog_outfile, "w"))) {
>   		/* create the output file for the sysfs msglog */
>

Acked-by: Ivan Hu <ivan.hu at canonical.com>