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Message-ID: <CAOQ4uxiuF7qfUjmSHu1RgwcEhDvbU9nA6nFpMXCmrZ9qE4c4rw@mail.gmail.com>
Date: Mon, 9 May 2022 14:48:36 +0300
From: Amir Goldstein <amir73il@...il.com>
To: Dan Carpenter <dan.carpenter@...cle.com>
Cc: kbuild@...ts.01.org, kbuild test robot <lkp@...el.com>,
kbuild-all@...ts.01.org,
linux-kernel <linux-kernel@...r.kernel.org>,
Matthew Bobrowski <repnop@...gle.com>, Jan Kara <jack@...e.cz>
Subject: Re: [amir73il:fsnotify-fixes 2/2] fs/notify/fsnotify.c:540 fsnotify()
warn: variable dereferenced before check 'dir1' (see line 499)
On Mon, May 9, 2022 at 1:09 PM Dan Carpenter <dan.carpenter@...cle.com> wrote:
>
> tree: https://github.com/amir73il/linux fsnotify-fixes
> head: d25f3ce8da49ce1a3b0a0621f0bf7b1d6ba2dad6
> commit: d25f3ce8da49ce1a3b0a0621f0bf7b1d6ba2dad6 [2/2] fsnotify: send FS_RENAME to groups watching the moved inode
> config: s390-randconfig-m031-20220508 (https://download.01.org/0day-ci/archive/20220508/202205080346.m0fb3UXK-lkp@intel.com/config)
> compiler: s390-linux-gcc (GCC) 11.3.0
>
> 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>
>
> smatch warnings:
> fs/notify/fsnotify.c:540 fsnotify() warn: variable dereferenced before check 'dir1' (see line 499)
>
> vim +/dir1 +540 fs/notify/fsnotify.c
>
> 40a100d3adc1ad Amir Goldstein 2020-07-22 475 int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
> 40a100d3adc1ad Amir Goldstein 2020-07-22 476 const struct qstr *file_name, struct inode *inode, u32 cookie)
> 90586523eb4b34 Eric Paris 2009-05-21 477 {
> b54cecf5e2293d Amir Goldstein 2020-06-07 478 const struct path *path = fsnotify_data_path(data, data_type);
> 29335033c574a1 Gabriel Krisman Bertazi 2021-10-25 479 struct super_block *sb = fsnotify_data_sb(data, data_type);
> 3427ce71554123 Miklos Szeredi 2017-10-30 480 struct fsnotify_iter_info iter_info = {};
> 60f7ed8c7c4d06 Amir Goldstein 2018-09-01 481 struct mount *mnt = NULL;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 482 struct inode *dir1, *dir2;
> e54183fa7047c1 Amir Goldstein 2021-11-29 483 struct dentry *moved;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 484 int dir1_type = 0;
> 9385a84d7e1f65 Jan Kara 2016-11-10 485 int ret = 0;
> 71d734103edfa2 Mel Gorman 2020-07-08 486 __u32 test_mask, marks_mask;
> 90586523eb4b34 Eric Paris 2009-05-21 487
> 71d734103edfa2 Mel Gorman 2020-07-08 488 if (path)
> aa93bdc5500cc9 Amir Goldstein 2020-03-19 489 mnt = real_mount(path->mnt);
> 3a9fb89f4cd04c Eric Paris 2009-12-17 490
> 40a100d3adc1ad Amir Goldstein 2020-07-22 491 if (!inode) {
> 40a100d3adc1ad Amir Goldstein 2020-07-22 492 /* Dirent event - report on TYPE_INODE to dir */
> 40a100d3adc1ad Amir Goldstein 2020-07-22 493 inode = dir;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 494 } else if (mask & FS_RENAME) {
> d25f3ce8da49ce Amir Goldstein 2022-05-07 495 /* For FS_RENAME, dir1 is old_dir and dir2 is new_dir */
> e54183fa7047c1 Amir Goldstein 2021-11-29 496 moved = fsnotify_data_dentry(data, data_type);
> d25f3ce8da49ce Amir Goldstein 2022-05-07 497 dir1 = moved->d_parent->d_inode;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 498 dir2 = dir;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 @499 if (dir1->i_fsnotify_marks || dir2->i_fsnotify_marks)
> ^^^^^^^^^^^^^^^^^^^^^^
> Dereference
>
> d25f3ce8da49ce Amir Goldstein 2022-05-07 500 dir1_type = FSNOTIFY_ITER_TYPE_OLD_DIR;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 501 /*
> d25f3ce8da49ce Amir Goldstein 2022-05-07 502 * Send FS_RENAME to groups watching the moved inode itself
> d25f3ce8da49ce Amir Goldstein 2022-05-07 503 * only if the moved inode is a non-dir.
> d25f3ce8da49ce Amir Goldstein 2022-05-07 504 * Sending FS_RENAME to a moved watched directory would be
> d25f3ce8da49ce Amir Goldstein 2022-05-07 505 * confusing and FS_MOVE_SELF provided enough information to
> d25f3ce8da49ce Amir Goldstein 2022-05-07 506 * track the movements of a watched directory.
> d25f3ce8da49ce Amir Goldstein 2022-05-07 507 */
> d25f3ce8da49ce Amir Goldstein 2022-05-07 508 if (mask & FS_ISDIR)
> d25f3ce8da49ce Amir Goldstein 2022-05-07 509 inode = NULL;
> 40a100d3adc1ad Amir Goldstein 2020-07-22 510 } else if (mask & FS_EVENT_ON_CHILD) {
> 40a100d3adc1ad Amir Goldstein 2020-07-22 511 /*
> fecc4559780d52 Amir Goldstein 2020-12-02 512 * Event on child - report on TYPE_PARENT to dir if it is
> fecc4559780d52 Amir Goldstein 2020-12-02 513 * watching children and on TYPE_INODE to child.
> 40a100d3adc1ad Amir Goldstein 2020-07-22 514 */
> d25f3ce8da49ce Amir Goldstein 2022-05-07 515 dir1 = dir;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 516 dir2 = NULL;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 517 if (dir1->i_fsnotify_marks)
> ^^^^^^^^^^^^^^^^^^^^^^
> Dereference
>
> d25f3ce8da49ce Amir Goldstein 2022-05-07 518 dir1_type = FSNOTIFY_ITER_TYPE_PARENT;
> 40a100d3adc1ad Amir Goldstein 2020-07-22 519 }
> 497b0c5a7c0688 Amir Goldstein 2020-07-16 520
> 7c49b8616460eb Dave Hansen 2015-09-04 521 /*
> 7c49b8616460eb Dave Hansen 2015-09-04 522 * Optimization: srcu_read_lock() has a memory barrier which can
> 7c49b8616460eb Dave Hansen 2015-09-04 523 * be expensive. It protects walking the *_fsnotify_marks lists.
> 7c49b8616460eb Dave Hansen 2015-09-04 524 * However, if we do not walk the lists, we do not have to do
> 7c49b8616460eb Dave Hansen 2015-09-04 525 * SRCU because we have no references to any objects and do not
> 7c49b8616460eb Dave Hansen 2015-09-04 526 * need SRCU to keep them "alive".
> 7c49b8616460eb Dave Hansen 2015-09-04 527 */
> 9b93f33105f5f9 Amir Goldstein 2020-07-16 528 if (!sb->s_fsnotify_marks &&
> 497b0c5a7c0688 Amir Goldstein 2020-07-16 529 (!mnt || !mnt->mnt_fsnotify_marks) &&
> 9b93f33105f5f9 Amir Goldstein 2020-07-16 530 (!inode || !inode->i_fsnotify_marks) &&
> d25f3ce8da49ce Amir Goldstein 2022-05-07 531 !dir1_type)
> 7c49b8616460eb Dave Hansen 2015-09-04 532 return 0;
> 71d734103edfa2 Mel Gorman 2020-07-08 533
> 9b93f33105f5f9 Amir Goldstein 2020-07-16 534 marks_mask = sb->s_fsnotify_mask;
> 71d734103edfa2 Mel Gorman 2020-07-08 535 if (mnt)
> 71d734103edfa2 Mel Gorman 2020-07-08 536 marks_mask |= mnt->mnt_fsnotify_mask;
> 9b93f33105f5f9 Amir Goldstein 2020-07-16 537 if (inode)
> 9b93f33105f5f9 Amir Goldstein 2020-07-16 538 marks_mask |= inode->i_fsnotify_mask;
> d25f3ce8da49ce Amir Goldstein 2022-05-07 539 if (dir1_type) {
> d25f3ce8da49ce Amir Goldstein 2022-05-07 @540 if (dir1)
>
> If "dir1_type" is set then we have already dereferenced "dir1". I guess
> this unnecessary NULL check is something that probably wouldn't bother
> a human reader too much...
True !!dir1_type means !!dir1.
We could get rid of if (dir1)
but I should note that I did not post this patch for review, this is an untested
patch that I pushed to a branch on my private github.
It is very generous of kbuild testbot to test any branch I push to my
private github,
but as much as I can recall, I never asked for it...
Thanks,
Amir.
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