On Thu, Nov 29, 2007 at 02:45:23PM -0500, Chuck Ebbert wrote:
> Original report: https://bugzilla.redhat.com/show_bug.cgi?id=404201
>
> The test case below, taken from the LTP test code, prints -1 (as
> expected) on 2.6.22 and 0 on 2.6.23. It tries to remap an out-of-range
> page. Proposed patch follows the program. Bug was apparently caused by
> commit 54cb8821de07f2ffcd28c380ce9b93d5784b40d7.
Ah, that's not such good behaviour anyway. mmap is allowed to map
outside the file offset, so you're telling me that remap_file_pages
just magically should not be allowed to remap these...?
> Patch:
>
> Signed-off-by: Supriya Kannery <[email protected]>
>
> --- linux-2.6.23/mm/fremap.c.orig 2007-11-22 00:56:09.000000000 -0600
> +++ linux-2.6.23/mm/fremap.c 2007-11-26 03:08:55.000000000 -0600
> @@ -124,6 +124,7 @@ asmlinkage long sys_remap_file_pages(uns
> struct vm_area_struct *vma;
> int err = -EINVAL;
> int has_write_lock = 0;
> + unsigned long f_size = 0;
>
> if (__prot)
> return err;
> @@ -181,6 +182,14 @@ asmlinkage long sys_remap_file_pages(uns
> goto retry;
> }
> mapping = vma->vm_file->f_mapping;
> +
> + f_size = i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1;
> + f_size = f_size >> PAGE_CACHE_SHIFT;
> + if ((pgoff + size >> PAGE_CACHE_SHIFT) > f_size) {
> + err = -EINVAL;
> + goto out;
> + }
> +
> /*
> * page_mkclean doesn't work on nonlinear vmas, so if
> * dirty pages need to be accounted, emulate with linear
I don't think there is anything preventing truncate races here. Theoretically
we could do it by taking i_mutex around here, but anyway then a subsequent
truncate is just going to be able to cause the mapping to be out of bounds
anyway.
If it were any other syscall than remap_file_pages, I'd be much more
hesitant to say this: I propose we change the test case instead. I
also changed other elements of the API, and we had the result tested
and verified by Oracle...
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