bad stdout handling

[guijan]

We don't need to know the path of stdout. It doesn't even necessarily have one. The code suffers from the TOCTTOU mentioned in #244, and it also uses /proc (a Linux extension) on non-Linux systems, so it's possible to affect the behavior of scrot by creating a /proc/self/fd/1 file on non-Linux systems.

scrot/src/options.c

Lines 339 to 348 in 99be99f

	static const char *getPathOfStdout(void)
	{
	const char *paths[] = { "/dev/stdout", "/dev/fd/1", "/proc/self/fd/1" };
	for (size_t i = 0; i < ARRAY_COUNT(paths); ++i) {
	if (accessFileOk(paths[i]))
	return paths[i];
	}
	err(EXIT_FAILURE, "access to stdout failed");
	}

This is probably because the imlib APIs we use want an output filename instead of an output file descriptor which is a design bug in imlib because it creates more races and unnecessarily limits the usefulness of the library (can't pick whether or not to overwrite a file, for instance). I looked at the headers of Imlib 1.10.0 and there is no function that writes an image to a given fd.

Imlib has added a function to address this in 1.11.0 on scrot's request, we need to migrate to it.