Re: [PATCH] ntfs: prevent write access to $MFT inode

Hi Hongling,

kernel test robot noticed the following build warnings:

[auto build test WARNING on brauner-vfs/vfs.all]
[also build test WARNING on linus/master v7.2-rc7 next-20260814]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Hongling-Zeng/ntfs-prevent-write-access-to-MFT-inode/20260814-004837
base:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git vfs.all
patch link:    https://lore.kernel.org/r/20260702063529.45448-1-zenghongling%40kylinos.cn
patch subject: [PATCH] ntfs: prevent write access to $MFT inode
config: um-randconfig-r071-20260815 (https://download.01.org/0day-ci/archive/20260815/[email protected]/config)
compiler: clang version 22.1.3 (https://github.com/llvm/llvm-project e9846648fd6183ee6d8cbdb4502213fcf902a211)
smatch: v0.5.0-9187-g5189e3fb
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260815/[email protected]/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All warnings (new ones prefixed by >>):

   In file included from fs/ntfs/file.c:9:
   In file included from include/linux/writeback.h:13:
   In file included from include/linux/blk_types.h:10:
   In file included from include/linux/bvec.h:10:
   In file included from include/linux/highmem.h:12:
   In file included from include/linux/hardirq.h:11:
   In file included from arch/um/include/asm/hardirq.h:24:
   In file included from include/linux/irq.h:20:
   In file included from include/linux/io.h:12:
   In file included from arch/um/include/asm/io.h:24:
   include/asm-generic/io.h:1209:55: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
    1209 |         return (port > MMIO_UPPER_LIMIT) ? NULL : PCI_IOBASE + port;
         |                                                   ~~~~~~~~~~ ^
>> fs/ntfs/file.c:555:5: warning: format specifies type 'unsigned long' but the argument has type 'u64' (aka 'unsigned long long') [-Wformat]
     554 |                 ntfs_error(vi->i_sb, "Attempt to write to $MFT denied (mft_no: 0x%lx)",
         |                                                                                  ~~~
         |                                                                                  %llx
     555 |                                 ni->mft_no);
         |                                 ^~~~~~~~~~
   fs/ntfs/debug.h:59:66: note: expanded from macro 'ntfs_error'
      59 | #define ntfs_error(sb, f, a...)         __ntfs_error(__func__, sb, f, ##a)
         |                                                                    ~    ^
   fs/ntfs/file.c:632:5: warning: format specifies type 'unsigned long' but the argument has type 'u64' (aka 'unsigned long long') [-Wformat]
     631 |                 ntfs_error(inode->i_sb, "Attempt to write to $MFT via mmap denied (mft_no: 0x%lx)",
         |                                                                                              ~~~
         |                                                                                              %llx
     632 |                                 ni->mft_no);
         |                                 ^~~~~~~~~~
   fs/ntfs/debug.h:59:66: note: expanded from macro 'ntfs_error'
      59 | #define ntfs_error(sb, f, a...)         __ntfs_error(__func__, sb, f, ##a)
         |                                                                    ~    ^
   3 warnings generated.


vim +555 fs/ntfs/file.c

   537	
   538	static ssize_t ntfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
   539	{
   540		struct file *file = iocb->ki_filp;
   541		struct inode *vi = file->f_mapping->host;
   542		struct ntfs_inode *ni = NTFS_I(vi);
   543		struct ntfs_volume *vol = ni->vol;
   544		ssize_t ret;
   545		ssize_t count;
   546		loff_t pos;
   547		int err;
   548		loff_t old_data_size, old_init_size;
   549	
   550		if (NVolShutdown(vol))
   551			return -EIO;
   552	
   553		if (ni->mft_no == FILE_MFT) {
   554			ntfs_error(vi->i_sb, "Attempt to write to $MFT denied (mft_no: 0x%lx)",
 > 555					ni->mft_no);
   556			return -EACCES;
   557		}
   558	
   559		if (NInoEncrypted(ni)) {
   560			ntfs_error(vi->i_sb, "Writing for %s files is not supported yet",
   561				   NInoCompressed(ni) ? "Compressed" : "Encrypted");
   562			return -EOPNOTSUPP;
   563		}
   564	
   565		if (NInoCompressed(ni) && iocb->ki_flags & IOCB_DIRECT)
   566			return -EOPNOTSUPP;
   567	
   568		if (iocb->ki_flags & IOCB_NOWAIT) {
   569			if (!inode_trylock(vi))
   570				return -EAGAIN;
   571		} else
   572			inode_lock(vi);
   573	
   574		ret = generic_write_checks(iocb, from);
   575		if (ret <= 0)
   576			goto out_lock;
   577	
   578		err = file_modified(iocb->ki_filp);
   579		if (err) {
   580			ret = err;
   581			goto out_lock;
   582		}
   583	
   584		if (!(vol->vol_flags & VOLUME_IS_DIRTY))
   585			ntfs_set_volume_flags(vol, VOLUME_IS_DIRTY);
   586	
   587		pos = iocb->ki_pos;
   588		count = ret;
   589	
   590		old_data_size = ni->data_size;
   591		old_init_size = ni->initialized_size;
   592	
   593		if (NInoNonResident(ni) && NInoCompressed(ni)) {
   594			ret = ntfs_compress_write(ni, pos, count, from);
   595			if (ret > 0)
   596				iocb->ki_pos += ret;
   597			goto out;
   598		}
   599	
   600		if (NInoNonResident(ni) && iocb->ki_flags & IOCB_DIRECT)
   601			ret = ntfs_dio_write_iter(iocb, from);
   602		else
   603			ret = iomap_file_buffered_write(iocb, from, &ntfs_write_iomap_ops,
   604					&ntfs_iomap_folio_ops, NULL);
   605	out:
   606		if (ret < 0 && ret != -EIOCBQUEUED) {
   607			if (ni->initialized_size != old_init_size) {
   608				mutex_lock(&ni->mrec_lock);
   609				ntfs_attr_set_initialized_size(ni, old_init_size);
   610				mutex_unlock(&ni->mrec_lock);
   611			}
   612			if (ni->data_size != old_data_size) {
   613				truncate_setsize(vi, old_data_size);
   614				ntfs_attr_truncate(ni, old_data_size);
   615			}
   616		}
   617	out_lock:
   618		inode_unlock(vi);
   619		if (ret > 0)
   620			ret = generic_write_sync(iocb, ret);
   621		return ret;
   622	}
   623