Messages in this thread | | | From | Nadav Amit <> | Subject | Re: [PATCH] hugetlbfs: change put_page/unlock_page order in hugetlbfs_fallocate() | Date | Sun, 27 Aug 2017 20:08:58 +0000 |
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Mike Kravetz <mike.kravetz@oracle.com> wrote:
> On 08/26/2017 12:11 PM, Nadav Amit wrote: >> hugetlfs_fallocate() currently performs put_page() before unlock_page(). >> This scenario opens a small time window, from the time the page is added >> to the page cache, until it is unlocked, in which the page might be >> removed from the page-cache by another core. If the page is removed >> during this time windows, it might cause a memory corruption, as the >> wrong page will be unlocked. >> >> It is arguable whether this scenario can happen in a real system, and >> there are several mitigating factors. The issue was found by code >> inspection (actually grep), and not by actually triggering the flow. >> Yet, since putting the page before unlocking is incorrect it should be >> fixed, if only to prevent future breakage or someone copy-pasting this >> code. >> >> Fixes: 70c3547e36f5c ("hugetlbfs: add hugetlbfs_fallocate()") >> >> cc: Eric Biggers <ebiggers3@gmail.com> >> cc: Mike Kravetz <mike.kravetz@oracle.com> >> >> Signed-off-by: Nadav Amit <namit@vmware.com> > > Thank you Nadav.
No problem.
> > Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> > > Since hugetlbfs is an in memory filesystem, the only way one 'should' be > able to remove a page (file content) is through an inode operation such as > truncate, hole punch, or unlink. That was the basis for my response that > the inode lock would be required for page freeing. > > Eric's question about sys_fadvise64(POSIX_FADV_DONTNEED) is interesting. > I was expecting to see a check for hugetlbfs pages and exit (without > modification) if encountered. A quick review of the code did not find > any such checks. > > I'll take a closer look to determine exactly how hugetlbfs files are > handled. IMO, there should be something similar to the DAX check where > the routine quickly exits.
I did not cc stable when submitting the patch, based on your previous response. Let me know if you want me to send v2 which does so.
Thanks, Nadav
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