[FFmpeg-devel] [PATCH V2 1/7] libavdevice/v4l2.c: fix build warning for [-Wformat-truncation=]

[Reimar Döffinger]

> On 27 Feb 2021, at 06:37, Guo, Yejun <yejun.guo at intel.com> wrote:
> 
> 
>> -----Original Message-----
>> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Reimar
>> D?ffinger
>>> 
> 
> For the code in this function, max length of file name is fixed, see the code below.
> Anyway, it still increases the on-stack variable size which might have potential security
> issue.
> 
>        snprintf(device_name, sizeof(device_name), "/dev/%s", entry->d_name);
> 
> 'man readdir' shows:
>           struct dirent {
>               ino_t          d_ino;       /* Inode number */
>               off_t          d_off;       /* Not an offset; see below */
>               unsigned short d_reclen;    /* Length of this record */
>               unsigned char  d_type;      /* Type of file; not supported
>                                              by all filesystem types */
>               char           d_name[256]; /* Null-terminated filename */
>           };

The size is not standardised.
E.g. the OSX manpage has:
     struct dirent { /* when _DARWIN_FEATURE_64_BIT_INODE is defined */
             ino_t      d_fileno;     /* file number of entry */
             __uint64_t d_seekoff;    /* seek offset (optional, used by servers)
 */
             __uint16_t d_reclen;     /* length of this record */
             __uint16_t d_namlen;     /* length of string in d_name */
             __uint8_t  d_type;       /* file type, see below */
             char    d_name[1024];    /* name must be no longer than this */
     };