[PATCH 7/8] btrfs: don't allow any modifications to an immutable file

Darrick J. Wong
2019-04-17T19:05:19Z

From: Darrick J. Wong <darrick.wong@oracle.com>

Don't allow any modifications to a file that's marked immutable, which
means that we have to flush all the writable pages to make the readonly
and we have to check the setattr/setflags parameters more closely.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/btrfs/ioctl.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 47 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index cd4e693406a0..632600e4be0a 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -180,6 +180,44 @@ static int check_fsflags(unsigned int flags)
return 0;
}

+/* Do all the prep work to check immutable status and all that. */
+static int btrfs_ioctl_check_immutable(struct inode *inode,
+ unsigned int fsflags,
+ const unsigned int immutable_fsflag)
+{
+ struct btrfs_inode *binode = BTRFS_I(inode);
+ int ret;
+
+ /*
+ * Wait for all pending directio and then flush all the dirty pages
+ * for this file. The flush marks all the pages readonly, so any
+ * subsequent attempt to write to the file (particularly mmap pages)
+ * will come through the filesystem and fail.
+ */
+ if (S_ISREG(inode->i_mode) && !IS_IMMUTABLE(inode) &&
+ (fsflags & immutable_fsflag)) {
+ inode_dio_wait(inode);
+ ret = filemap_write_and_wait(inode->i_mapping);
+ if (ret)
+ return ret;
+ }
+
+ /*
+ * If immutable is set and we are not clearing it, we're not allowed to
+ * change anything else in the inode. Don't error out if we're only
+ * trying to set immutable on an immutable file.
+ */
+ if (!(binode->flags & BTRFS_INODE_IMMUTABLE) ||
+ !(fsflags & immutable_fsflag))
+ return 0;
+
+ if ((binode->flags & ~BTRFS_INODE_IMMUTABLE) !=
+ (fsflags & ~immutable_fsflag))
+ return -EPERM;
+
+ return 0;
+}
+
static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
{
struct inode *inode = file_inode(file);
@@ -225,6 +263,10 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
}
}

+ ret = btrfs_ioctl_check_immutable(inode, fsflags, FS_IMMUTABLE_FL);
+ if (ret)
+ goto out_unlock;
+
if (fsflags & FS_SYNC_FL)
binode->flags |= BTRFS_INODE_SYNC;
else
@@ -433,6 +475,11 @@ static int btrfs_ioctl_fssetxattr(struct file *file, void __user *arg)
goto out_unlock;
}

+ ret = btrfs_ioctl_check_immutable(inode, fa.fsx_xflags,
+ FS_XFLAG_IMMUTABLE);
+ if (ret)
+ goto out_unlock;
+
if (fa.fsx_xflags & FS_XFLAG_SYNC)
binode->flags |= BTRFS_INODE_SYNC;
else