linux-kernel - [driver-core:debugfs_cleanup 1/2] fs/d_path.c:59 prepend() warn: unsigned 'p->len' is never less than zero.

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Date:   Thu, 30 Sep 2021 12:17:32 +0800
From:   kernel test robot <lkp@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     kbuild-all@...ts.01.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: [driver-core:debugfs_cleanup 1/2] fs/d_path.c:59 prepend() warn:
 unsigned 'p->len' is never less than zero.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git debugfs_cleanup
head:   c4535d1b074f3fdd9476e83526d4e9b53f41a7b5
commit: 473082c5bbad92c5909ccf75fb28df699b94de82 [1/2] fs: make d_path-like functions all have unsigned size
config: i386-randconfig-m021-20210929 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0

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

smatch warnings:
fs/d_path.c:59 prepend() warn: unsigned 'p->len' is never less than zero.

vim +59 fs/d_path.c

b0cfcdd9b9672ea Linus Torvalds 2021-07-16  55  
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  56  static bool prepend(struct prepend_buffer *p, const char *str, int namelen)
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  57  {
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  58  	// Already overflowed?
b0cfcdd9b9672ea Linus Torvalds 2021-07-16 @59  	if (p->len < 0)
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  60  		return false;
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  61  
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  62  	// Will overflow?
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  63  	if (p->len < namelen) {
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  64  		// Fill as much as possible from the end of the name
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  65  		str += namelen - p->len;
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  66  		p->buf -= p->len;
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  67  		prepend_copy(p->buf, str, p->len);
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  68  		p->len = -1;
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  69  		return false;
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  70  	}
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  71  
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  72  	// Fits fully
ad08ae586586ea9 Al Viro        2021-05-12  73  	p->len -= namelen;
ad08ae586586ea9 Al Viro        2021-05-12  74  	p->buf -= namelen;
b0cfcdd9b9672ea Linus Torvalds 2021-07-16  75  	return prepend_copy(p->buf, str, namelen);
7a5cf791a747640 Al Viro        2018-03-05  76  }
7a5cf791a747640 Al Viro        2018-03-05  77  

:::::: The code at line 59 was first introduced by commit
:::::: b0cfcdd9b9672ea90642f33d6c0dd8516553adf2 d_path: make 'prepend()' fill up the buffer exactly on overflow

:::::: TO: Linus Torvalds <torvalds@...ux-foundation.org>
:::::: CC: Linus Torvalds <torvalds@...ux-foundation.org>

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

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