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authorNadav Amit <namit@vmware.com>2017-11-29 16:11:33 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-11-29 18:40:43 -0800
commit72639e6df4128dfde8fee7638a35be7db8114000 (patch)
treeaf7edb7d7d722fbc0f3b4c5ea7ca5c6fb4c101e8 /fs/hugetlbfs
parentf4f0a3d85b50a65a348e2b8635041d6b30f01deb (diff)
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 code. 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 3a77d214807c ("mm: fadvise: avoid fadvise for fs without backing device")" Link: http://lkml.kernel.org/r/20170826191124.51642-1-namit@vmware.com Fixes: 70c3547e36f5c ("hugetlbfs: add hugetlbfs_fallocate()") Signed-off-by: Nadav Amit <namit@vmware.com> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Eric Biggers <ebiggers3@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/hugetlbfs')
-rw-r--r--fs/hugetlbfs/inode.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 1e76730aac0d..8a85f3f53446 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -639,11 +639,11 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
/*
- * 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()
*/
- put_page(page);
unlock_page(page);
+ put_page(page);
}
if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)

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