vfs: remap helper should update destination inode metadata

Extend generic_remap_file_range_prep to handle inode metadata updates
when remapping into a file.  If the operation can possibly alter the
file contents, we must update the ctime and mtime and remove security
privileges, just like we do for regular file writes.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index ebcbfc4f2907..b61bd3fc7154 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1820,6 +1820,25 @@ int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 	if (ret)
 		return ret;
 
+	/* If can't alter the file contents, we're done. */
+	if (!(remap_flags & REMAP_FILE_DEDUP)) {
+		/* Update the timestamps, since we can alter file contents. */
+		if (!(file_out->f_mode & FMODE_NOCMTIME)) {
+			ret = file_update_time(file_out);
+			if (ret)
+				return ret;
+		}
+
+		/*
+		 * Clear the security bits if the process is not being run by
+		 * root.  This keeps people from modifying setuid and setgid
+		 * binaries.
+		 */
+		ret = file_remove_privs(file_out);
+		if (ret)
+			return ret;
+	}
+
 	return 1;
 }
 EXPORT_SYMBOL(generic_remap_file_range_prep);