Re: [PATCH] check mapped ranges on sysfs resource files (for 2.6.27)

[Jesse Barnes <jbarnes@virtuousgeek.org>]

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On Thursday, October 2, 2008 4:30 pm Linus Torvalds wrote:
> On Thu, 2 Oct 2008, Jesse Barnes wrote:
> > +	unsigned long map_len = vma->vm_end - vma->vm_start;
> > +	unsigned long map_offset = vma->vm_pgoff << PAGE_SHIFT;
>
> This seems broken for big vm_pgoff values, where that shift will
> potentially overflow, no?

Ah yes, exactly what we want to be checking for in fact.

> Also, it strikes me that we don't seem to check that the resource start is
> page-aligned. We just do
>
> 	vma->vm_pgoff += start >> PAGE_SHIFT;
>
> without checking if we just dropped low bits from 'start'.

Hm, yeah looks like that's a long standing issue...

> Of course, if the length of the resource is bigger than a page, I guess
> the resource is guaranteed to be at least page-aligned, so maybe the
> length check - if it was correct - would be sufficient.
>
> Anyway, it would be *much* better to do the length check in pages rather
> than in bytes, to avoid the overflow condition.
>
> Can somebody test if something like this works? It also prints the actual
> name of the device, not just a random BAR number (but it will print
> everyting in PFN's, I hate potentially losing information).

Yeah, looks much better.  I was using this silly test program to see if the 
earlier code worked.  Just pass in both valid and invalid sizes.

Jesse

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#include <errno.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>

int main(int argc, char *argv[])
{
	size_t len;
	int fd;
	void *ptr;

	if (argc != 3) {
		fprintf(stderr, "usage: %s <file> <mapsize>\n",
			argv[0]);
		return -1;
	}

	len = atoi(argv[2]);

	fd = open(argv[1], O_RDONLY);
	if (fd == -1) {
		fprintf(stderr, "open failed: %s\n", strerror(errno));
		return errno;
	}

	ptr = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
	if (ptr == MAP_FAILED) {
		fprintf(stderr, "mmap failed: %s\n", strerror(errno));
		return errno;
	}

	printf("mmap of %s with size %zd succeeded\n", argv[1], len);

	munmap(ptr, len); /* ignore any errors, we don't care */
	close(fd);
	return 0;
}