Re: [PATCH] usb: mon: Fix slab-out-of-bounds in mon_bin_event due to unsafe URB transfer_buffer access

[kernel test robot <lkp@intel.com>]

Hi Arnaud,

kernel test robot noticed the following build warnings:

[auto build test WARNING on usb/usb-testing]
[also build test WARNING on usb/usb-next usb/usb-linus westeri-thunderbolt/next linus/master v6.16-rc7 next-20250722]
[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/Arnaud-Lecomte/usb-mon-Fix-slab-out-of-bounds-in-mon_bin_event-due-to-unsafe-URB-transfer_buffer-access/20250721-040222
base:   https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
patch link:    https://lore.kernel.org/r/20250720200057.19720-1-contact%40arnaud-lcm.com
patch subject: [PATCH] usb: mon: Fix slab-out-of-bounds in mon_bin_event due to unsafe URB transfer_buffer access
config: m68k-randconfig-r073-20250723 (https://download.01.org/0day-ci/archive/20250723/202507230548.g6zwppI6-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 14.3.0

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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202507230548.g6zwppI6-lkp@intel.com/

smatch warnings:
drivers/usb/mon/mon_bin.c:422 mon_bin_get_data() warn: unsigned 'mon_copy_to_buff(rp, offset, urb->transfer_buffer, length)' is never less than zero.
drivers/usb/mon/mon_bin.c:443 mon_bin_get_data() warn: unsigned 'offset' is never less than zero.

vim +422 drivers/usb/mon/mon_bin.c

   409	
   410	static unsigned int mon_bin_get_data(const struct mon_reader_bin *rp,
   411	    unsigned int offset, struct urb *urb, unsigned int length,
   412	    char *flag)
   413	{
   414		int i;
   415		struct scatterlist *sg;
   416		unsigned int this_len;
   417	
   418		*flag = 0;
   419		if (urb->num_sgs == 0) {
   420			if (
   421				urb->transfer_buffer == NULL ||
 > 422				mon_copy_to_buff(rp, offset, urb->transfer_buffer, length) < 0
   423			) {
   424				*flag = 'Z';
   425				return length;
   426			}
   427			length = 0;
   428	
   429		} else {
   430			/* If IOMMU coalescing occurred, we cannot trust sg_page */
   431			if (urb->transfer_flags & URB_DMA_SG_COMBINED) {
   432				*flag = 'D';
   433				return length;
   434			}
   435	
   436			/* Copy up to the first non-addressable segment */
   437			for_each_sg(urb->sg, sg, urb->num_sgs, i) {
   438				if (length == 0 || PageHighMem(sg_page(sg)))
   439					break;
   440				this_len = min_t(unsigned int, sg->length, length);
   441				offset = mon_copy_to_buff(rp, offset, sg_virt(sg),
   442						this_len);
 > 443				if (offset < 0) {
   444					*flag = 'Z';
   445					return length;
   446				}
   447				length -= this_len;
   448			}
   449			if (i == 0)
   450				*flag = 'D';
   451		}
   452	
   453		return length;
   454	}
   455	

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