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vfs: cap dedupe request structure size at PAGE_SIZE

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Kirill A Shutemov reports that the kernel doesn't try to cap dest_count
in any way, and uses the number to allocate kernel memory.  This causes
high order allocation warnings in the kernel log if someone passes in a
big enough value.  We should clamp the allocation at PAGE_SIZE to avoid
stressing the VM.

The two existing users of the dedupe ioctl never send more than 120
requests, so we can safely clamp dest_range at PAGE_SIZE, because with
4k pages we can handle up to 127 dedupe candidates.  Given the max
extent length of 16MB, we can end up doing 2GB of IO which is plenty.

[ Note: the "offsetof()" can't overflow, because 'count' is just a
  16-bit integer.  That's not obvious in the limited context of the
  patch, so I'm noting it here because it made me go look.  - Linus ]

Reported-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Darrick J. Wong 2016-09-14 20:20:44 -07:00 committed by Linus Torvalds
parent 5297e0f0fe
commit b71dbf1032
1 changed files with 4 additions and 0 deletions
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4
fs/ioctl.c
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@ -582,6 +582,10 @@ static int ioctl_file_dedupe_range(struct file *file, void __user *arg)
}
size = offsetof(struct file_dedupe_range __user, info[count]);
if (size > PAGE_SIZE) {
ret = -ENOMEM;
goto out;
}
same = memdup_user(argp, size);
if (IS_ERR(same)) {