From b71dbf1032f546bf3efd60fb5d9d0cefd200a508 Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Wed, 14 Sep 2016 20:20:44 -0700 Subject: [PATCH] vfs: cap dedupe request structure size at PAGE_SIZE 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" Signed-off-by: Darrick J. Wong Signed-off-by: Linus Torvalds --- fs/ioctl.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/ioctl.c b/fs/ioctl.c index 26aba0942a98..c415668c86d4 100644 --- a/fs/ioctl.c +++ b/fs/ioctl.c @@ -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)) {