linux-kernel - fs/vboxsf/super.c:390 vboxsf_parse_monolithic() warn: impossible condition == (255)) => ((-128)-127 == 255)'

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Message-ID: <20200824131005.GO1793@kadam>
Date:   Mon, 24 Aug 2020 16:10:06 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     kbuild@...ts.01.org, Hans de Goede <hdegoede@...hat.com>
Cc:     lkp@...el.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: fs/vboxsf/super.c:390 vboxsf_parse_monolithic() warn: impossible
 condition == (255)) => ((-128)-127 == 255)'

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   c3d8f220d01220a5b253e422be407d068dc65511
commit: 0fd169576648452725fa2949bf391d10883d3991 fs: Add VirtualBox guest shared folder (vboxsf) support
config: x86_64-randconfig-m001-20200824 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@...el.com>
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>

New smatch warnings:
fs/vboxsf/super.c:390 vboxsf_parse_monolithic() warn: impossible condition '(options[1] == (255)) => ((-128)-127 == 255)'

Old smatch warnings:
fs/vboxsf/super.c:391 vboxsf_parse_monolithic() warn: impossible condition '(options[2] == (254)) => ((-128)-127 == 254)'
fs/vboxsf/super.c:392 vboxsf_parse_monolithic() warn: impossible condition '(options[3] == (253)) => ((-128)-127 == 253)'

# https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0fd169576648452725fa2949bf391d10883d3991
git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
git fetch --no-tags linus master
git checkout 0fd169576648452725fa2949bf391d10883d3991
vim +390 fs/vboxsf/super.c

0fd16957664845 Hans de Goede 2019-12-12  385  static int vboxsf_parse_monolithic(struct fs_context *fc, void *data)
0fd16957664845 Hans de Goede 2019-12-12  386  {
0fd16957664845 Hans de Goede 2019-12-12  387  	char *options = data;
0fd16957664845 Hans de Goede 2019-12-12  388  
0fd16957664845 Hans de Goede 2019-12-12  389  	if (options && options[0] == VBSF_MOUNT_SIGNATURE_BYTE_0 &&
0fd16957664845 Hans de Goede 2019-12-12 @390  		       options[1] == VBSF_MOUNT_SIGNATURE_BYTE_1 &&
                                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Impossible.

0fd16957664845 Hans de Goede 2019-12-12  391  		       options[2] == VBSF_MOUNT_SIGNATURE_BYTE_2 &&
                                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
0fd16957664845 Hans de Goede 2019-12-12  392  		       options[3] == VBSF_MOUNT_SIGNATURE_BYTE_3) {
                                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
0fd16957664845 Hans de Goede 2019-12-12  393  		vbg_err("vboxsf: Old binary mount data not supported, remove obsolete mount.vboxsf and/or update your VBoxService.\n");
0fd16957664845 Hans de Goede 2019-12-12  394  		return -EINVAL;
0fd16957664845 Hans de Goede 2019-12-12  395  	}
0fd16957664845 Hans de Goede 2019-12-12  396  
0fd16957664845 Hans de Goede 2019-12-12  397  	return generic_parse_monolithic(fc, data);
0fd16957664845 Hans de Goede 2019-12-12  398  }

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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