f2fs: explicitly null-terminate the xattr list

commit e26b6d39270f5eab0087453d9b544189a38c8564 upstream.

When setting an xattr, explicitly null-terminate the xattr list.  This
eliminates the fragile assumption that the unused xattr space is always
zeroed.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/f2fs/xattr.c

@@ -754,6 +754,12 @@ retry:
 		memcpy(pval, value, size);
 		last->e_value_size = cpu_to_le16(size);
 		new_hsize += newsize;
+		/*
+		 * Explicitly add the null terminator.  The unused xattr space
+		 * is supposed to always be zeroed, which would make this
+		 * unnecessary, but don't depend on that.
+		 */
+		*(u32 *)((u8 *)last + newsize) = 0;
 	}
 
 	error = write_all_xattrs(inode, new_hsize, base_addr, ipage);