Re: [PATCH v3] hugetlbfs: Fix integer overflow check in hugetlbfs_file_mmap()

[kernel test robot]

Hi Linke,

kernel test robot noticed the following build warnings:

[auto build test WARNING on linus/master]
[also build test WARNING on v6.5-rc2 next-20230720]
[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/Linke-Li/hugetlbfs-Fix-integer-overflow-check-in-hugetlbfs_file_mmap/20230720-225128
base:   linus/master
patch link:    https://lore.kernel.org/r/tencent_C2D6865561F23A8141BB145149ACC682B408%40qq.com
patch subject: [PATCH v3] hugetlbfs: Fix integer overflow check in hugetlbfs_file_mmap()
config: s390-randconfig-r024-20230720 (https://download.01.org/0day-ci/archive/20230721/202307210737.HUPwpBdW-lkp@xxxxxxxxx/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
reproduce: (https://download.01.org/0day-ci/archive/20230721/202307210737.HUPwpBdW-lkp@xxxxxxxxx/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 <lkp@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202307210737.HUPwpBdW-lkp@xxxxxxxxx/

All warnings (new ones prefixed by >>):

>> fs/hugetlbfs/inode.c:157:25: warning: variable 'vma_len' is uninitialized when used here [-Wuninitialized]
     157 |         if (check_add_overflow(vma_len, (loff_t)vma->vm_pgoff << PAGE_SHIFT, &len))
         |                                ^~~~~~~
   include/linux/overflow.h:67:47: note: expanded from macro 'check_add_overflow'
      67 |         __must_check_overflow(__builtin_add_overflow(a, b, d))
         |                                                      ^
   fs/hugetlbfs/inode.c:123:21: note: initialize the variable 'vma_len' to silence this warning
     123 |         loff_t len, vma_len;
         |                            ^
         |                             = 0
   1 warning generated.


vim +/vma_len +157 fs/hugetlbfs/inode.c

   108	
   109	/*
   110	 * Mask used when checking the page offset value passed in via system
   111	 * calls.  This value will be converted to a loff_t which is signed.
   112	 * Therefore, we want to check the upper PAGE_SHIFT + 1 bits of the
   113	 * value.  The extra bit (- 1 in the shift value) is to take the sign
   114	 * bit into account.
   115	 */
   116	#define PGOFF_LOFFT_MAX \
   117		(((1UL << (PAGE_SHIFT + 1)) - 1) <<  (BITS_PER_LONG - (PAGE_SHIFT + 1)))
   118	
   119	static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
   120	{
   121		struct inode *inode = file_inode(file);
   122		struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);
   123		loff_t len, vma_len;
   124		int ret;
   125		struct hstate *h = hstate_file(file);
   126	
   127		/*
   128		 * vma address alignment (but not the pgoff alignment) has
   129		 * already been checked by prepare_hugepage_range.  If you add
   130		 * any error returns here, do so after setting VM_HUGETLB, so
   131		 * is_vm_hugetlb_page tests below unmap_region go the right
   132		 * way when do_mmap unwinds (may be important on powerpc
   133		 * and ia64).
   134		 */
   135		vm_flags_set(vma, VM_HUGETLB | VM_DONTEXPAND);
   136		vma->vm_ops = &hugetlb_vm_ops;
   137	
   138		ret = seal_check_future_write(info->seals, vma);
   139		if (ret)
   140			return ret;
   141	
   142		/*
   143		 * page based offset in vm_pgoff could be sufficiently large to
   144		 * overflow a loff_t when converted to byte offset.  This can
   145		 * only happen on architectures where sizeof(loff_t) ==
   146		 * sizeof(unsigned long).  So, only check in those instances.
   147		 */
   148		if (sizeof(unsigned long) == sizeof(loff_t)) {
   149			if (vma->vm_pgoff & PGOFF_LOFFT_MAX)
   150				return -EINVAL;
   151		}
   152	
   153		/* must be huge page aligned */
   154		if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))
   155			return -EINVAL;
   156	
 > 157		if (check_add_overflow(vma_len, (loff_t)vma->vm_pgoff << PAGE_SHIFT, &len))
   158			return -EINVAL;
   159	
   160		inode_lock(inode);
   161		file_accessed(file);
   162	
   163		ret = -ENOMEM;
   164		if (!hugetlb_reserve_pages(inode,
   165					vma->vm_pgoff >> huge_page_order(h),
   166					len >> huge_page_shift(h), vma,
   167					vma->vm_flags))
   168			goto out;
   169	
   170		ret = 0;
   171		if (vma->vm_flags & VM_WRITE && inode->i_size < len)
   172			i_size_write(inode, len);
   173	out:
   174		inode_unlock(inode);
   175	
   176		return ret;
   177	}
   178	

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