Re: [FFmpeg-devel] [PATCH v1] fftools/ffplay: Resolve input file path before processing

[Marton Balint <cus@passwd.hu>]

On Wed, 14 May 2025, Nicolas George wrote:

> Appaji (HE12025-05-14):
>> Fixes ticket: https://trac.ffmpeg.org/ticket/11574
>> 
>> Signed-off-by: Appaji <appaji12368@gmail.com>
>> ---
>>  fftools/ffplay.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>> 
>> diff --git a/fftools/ffplay.c b/fftools/ffplay.c
>> index 2a572fc3aa..42f0584b55 100644
>> --- a/fftools/ffplay.c
>> +++ b/fftools/ffplay.c
>> @@ -27,6 +27,7 @@
>>  #include "config_components.h"
>>  #include <math.h>
>>  #include <limits.h>
>> +#include <stdlib.h>
>>  #include <signal.h>
>>  #include <stdint.h>
>> 
>> @@ -3623,9 +3624,17 @@ static int opt_input_file(void *optctx, const char *filename)
>>                  filename, input_filename);
>>          return AVERROR(EINVAL);
>>      }
>> -    if (!strcmp(filename, "-"))
>> +
>> +    char resolved_path[PATH_MAX];
>> +
>> +    if (!realpath(filename, resolved_path)) {
>> +        av_log(NULL, AV_LOG_FATAL, "Failed to resolve path for '%s': %s\n", filename, strerror(errno));
>> +        return AVERROR(errno);
>> +    }
>> +
>
> Hi. Thanks for the patch. Did you test it with non-filenames arguments,
> for example http://…?
>
>> +    if (!strcmp(resolved_path, "-"))
>>          filename = "fd:";
>
> This should happen before resolution.
>
>> -    input_filename = av_strdup(filename);
>> +    input_filename = av_strdup(resolved_path);
>>      if (!input_filename)
>>          return AVERROR(ENOMEM);
>> 
>
> On the whole, I think you are going at it wrong: you are only fixing
> this for ffplay, not for ffprobe, ffmpeg and other applications built on
> the libraries, and resolving the path can have side effects, for example
> if you do not have permission on a parent of the current working
> directory.
>
> IMO, the correct way would be to add a stat() early in the opening of
> the file and test the device number. But that requires changing quite a
> lot of things.

Agreed. You should improve the probing function to fix the ticket, you can 
do a stat in v4l2_read_probe() in libavdevice/v4l2.c, check if it is a 
char device and try a V4L2 IOCTL on it to make sure it is a V4L2 device.

Regards,
Marton

>
> Regards,
>
> --
>  Nicolas George
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