[djwong-xfs:vectorized-scrub 154/352] fs/remap_range.c:629 generic_xchg_file_range_checks() warn: unsigned 'fxr->length' is never less than zero.

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git vectorized-scrub
head:   9716b2732a485c80e6988c5bdf42bd53d337773f
commit: 6420f9fb66b09f0f0dfa8c1bd45d010ce76adedc [154/352] vfs: introduce new file range exchange ioctl
config: h8300-randconfig-m031-20210702 (attached as .config)
compiler: h8300-linux-gcc (GCC) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

smatch warnings:
fs/remap_range.c:629 generic_xchg_file_range_checks() warn: unsigned 'fxr->length' is never less than zero.

vim +629 fs/remap_range.c

   583	
   584	/* Performs necessary checks before doing a range exchange. */
   585	static int generic_xchg_file_range_checks(struct file *file1,
   586						  struct file *file2,
   587						  struct file_xchg_range *fxr,
   588						  unsigned int blocksize)
   589	{
   590		struct inode *inode1 = file1->f_mapping->host;
   591		struct inode *inode2 = file2->f_mapping->host;
   592		uint64_t blkmask = blocksize - 1;
   593		int64_t test_len;
   594		uint64_t blen;
   595		loff_t size1, size2;
   596		int ret;
   597	
   598		/* Don't touch certain kinds of inodes */
   599		if (IS_IMMUTABLE(inode1) || IS_IMMUTABLE(inode2))
   600			return -EPERM;
   601		if (IS_SWAPFILE(inode1) || IS_SWAPFILE(inode2))
   602			return -ETXTBSY;
   603	
   604		size1 = i_size_read(inode1);
   605		size2 = i_size_read(inode2);
   606	
   607		/* Ranges cannot start after EOF. */
   608		if (fxr->file1_offset > size1 || fxr->file2_offset > size2)
   609			return -EINVAL;
   610	
   611		/*
   612		 * If the caller asked for full files, check that the offset/length
   613		 * values cover all of both files.
   614		 */
   615		if ((fxr->flags & FILE_XCHG_RANGE_FULL_FILES) &&
   616		    (fxr->file1_offset != 0 || fxr->file2_offset != 0 ||
   617		     fxr->length != size1 || fxr->length != size2))
   618			return -EDOM;
   619	
   620		/*
   621		 * If the caller said to exchange to EOF, we set the length of the
   622		 * request large enough to cover everything to the end of both files.
   623		 */
   624		if (fxr->flags & FILE_XCHG_RANGE_TO_EOF)
   625			fxr->length = max_t(int64_t, size1 - fxr->file1_offset,
   626						     size2 - fxr->file2_offset);
   627	
   628		/* No negative lengths */
 > 629		if (fxr->length < 0)
   630			return -EINVAL;
   631	
   632		/* The start of both ranges must be aligned to an fs block. */
   633		if (!IS_ALIGNED(fxr->file1_offset, blocksize) ||
   634		    !IS_ALIGNED(fxr->file2_offset, blocksize))
   635			return -EINVAL;
   636	
   637		/* Ensure offsets don't wrap. */
   638		if (fxr->file1_offset + fxr->length < fxr->file1_offset ||
   639		    fxr->file2_offset + fxr->length < fxr->file2_offset)
   640			return -EINVAL;
   641	
   642		/*
   643		 * We require both ranges to be within EOF, unless we're exchanging
   644		 * to EOF.  generic_xchg_range_prep already checked that both
   645		 * fxr->file1_offset and fxr->file2_offset are within EOF.
   646		 */
   647		if (!(fxr->flags & FILE_XCHG_RANGE_TO_EOF) &&
   648		    (fxr->file1_offset + fxr->length > size1 ||
   649		     fxr->file2_offset + fxr->length > size2))
   650			return -EINVAL;
   651	
   652		/*
   653		 * Make sure we don't hit any file size limits.  If we hit any size
   654		 * limits such that test_length was adjusted, we abort the whole
   655		 * operation.
   656		 */
   657		test_len = fxr->length;
   658		ret = generic_write_check_limits(file2, fxr->file2_offset, &test_len);
   659		if (ret)
   660			return ret;
   661		ret = generic_write_check_limits(file1, fxr->file1_offset, &test_len);
   662		if (ret)
   663			return ret;
   664		if (test_len != fxr->length)
   665			return -EINVAL;
   666	
   667		/*
   668		 * If the user wanted us to exchange up to the infile's EOF, round up
   669		 * to the next block boundary for this check.  Do the same for the
   670		 * outfile.
   671		 *
   672		 * Otherwise, reject the range length if it's not block aligned.  We
   673		 * already confirmed the starting offsets' block alignment.
   674		 */
   675		if (fxr->file1_offset + fxr->length == size1)
   676			blen = ALIGN(size1, blocksize) - fxr->file1_offset;
   677		else if (fxr->file2_offset + fxr->length == size2)
   678			blen = ALIGN(size2, blocksize) - fxr->file2_offset;
   679		else if (!IS_ALIGNED(fxr->length, blocksize))
   680			return -EINVAL;
   681		else
   682			blen = fxr->length;
   683	
   684		/* Don't allow overlapped exchanges within the same file. */
   685		if (inode1 == inode2 &&
   686		    fxr->file2_offset + blen > fxr->file1_offset &&
   687		    fxr->file1_offset + blen > fxr->file2_offset)
   688			return -EINVAL;
   689	
   690		/* If we already failed the freshness check, we're done. */
   691		ret = generic_xchg_file_range_check_fresh(inode2, fxr);
   692		if (ret)
   693			return ret;
   694	
   695		/*
   696		 * Ensure that we don't exchange a partial EOF block into the middle of
   697		 * another file.
   698		 */
   699		if ((fxr->length & blkmask) == 0)
   700			return 0;
   701	
   702		blen = fxr->length;
   703		if (fxr->file2_offset + blen < size2)
   704			blen &= ~blkmask;
   705	
   706		if (fxr->file1_offset + blen < size1)
   707			blen &= ~blkmask;
   708	
   709		return blen == fxr->length ? 0 : -EINVAL;
   710	}
   711	

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