Commit 72639e6d authored by Nadav Amit's avatar Nadav Amit Committed by Linus Torvalds

fs/hugetlbfs/inode.c: change put_page/unlock_page order in hugetlbfs_fallocate()

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

Mike said:
 "I am of the opinion that this does not need to be sent to stable.
  Although the ordering is current code is incorrect, there is no way
  for this to be a problem with current locking. In addition, I verified
  that the perhaps bigger issue with sys_fadvise64(POSIX_FADV_DONTNEED)
  for hugetlbfs and other filesystems is addressed in 3a77d214 ("mm:
  fadvise: avoid fadvise for fs without backing device")"

Fixes: 70c3547e ("hugetlbfs: add hugetlbfs_fallocate()")
Signed-off-by: default avatarNadav Amit <>
Reviewed-by: default avatarMike Kravetz <>
Acked-by: default avatarMichal Hocko <>
Cc: Eric Biggers <>
Cc: Mike Kravetz <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent f4f0a3d8
......@@ -639,11 +639,11 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
* page_put due to reference from alloc_huge_page()
* unlock_page because locked by add_to_page_cache()
* page_put due to reference from alloc_huge_page()
if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment