The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b5c40d598f5408bd0ca22dfffa82f03cd9433f23 Mon Sep 17 00:00:00 2001

From: Omar Sandoval osandov@fb.com Date: Tue, 22 May 2018 15:02:12 -0700 Subject: [PATCH] Btrfs: fix clone vs chattr NODATASUM race

In btrfs_clone_files(), we must check the NODATASUM flag while the inodes are locked. Otherwise, it's possible that btrfs_ioctl_setflags() will change the flags after we check and we can end up with a party checksummed file.

The race window is only a few instructions in size, between the if and the locks which is:

3834 if (S_ISDIR(src->i_mode) || S_ISDIR(inode->i_mode)) 3835 return -EISDIR;

where the setflags must be run and toggle the NODATASUM flag (provided the file size is 0). The clone will block on the inode lock, segflags takes the inode lock, changes flags, releases log and clone continues.

Not impossible but still needs a lot of bad luck to hit unintentionally.

Fixes: 0e7b824c4ef9 ("Btrfs: don't make a file partly checksummed through file clone") CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Omar Sandoval osandov@fb.com Reviewed-by: Nikolay Borisov nborisov@suse.com Reviewed-by: David Sterba dsterba@suse.com [ update changelog ] Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 743c4f1b8001..b9b779a4ab6e 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -3808,11 +3808,6 @@ static noinline int btrfs_clone_files(struct file *file, struct file *file_src, src->i_sb != inode->i_sb) return -EXDEV;

- /* don't make the dst file partly checksummed */ - if ((BTRFS_I(src)->flags & BTRFS_INODE_NODATASUM) != - (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) - return -EINVAL; - if (S_ISDIR(src->i_mode) || S_ISDIR(inode->i_mode)) return -EISDIR;

@@ -3822,6 +3817,13 @@ static noinline int btrfs_clone_files(struct file *file, struct file *file_src, inode_lock(src); }

+ /* don't make the dst file partly checksummed */ + if ((BTRFS_I(src)->flags & BTRFS_INODE_NODATASUM) != + (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) { + ret = -EINVAL; + goto out_unlock; + } + /* determine range to clone */ ret = -EINVAL; if (off + len > src->i_size || off + len < off)