Re: fs/namei.c:4875 vfs_rename() warn: variable dereferenced before check 'source' (see line 4830)

From: Jan Kara
Date: Mon Jul 03 2023 - 10:36:55 EST

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In reply to: Dan Carpenter: "fs/namei.c:4875 vfs_rename() warn: variable dereferenced before check 'source' (see line 4830)"
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On Mon 03-07-23 15:16:36, Dan Carpenter wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: 995b406c7e972fab181a4bb57f3b95e59b8e5bf3
> commit: 28eceeda130f5058074dd007d9c59d2e8bc5af2e fs: Lock moved directories
> config: x86_64-randconfig-m001-20230702 (https://download.01.org/0day-ci/archive/20230703/202307030026.9sE2pk2x-lkp@xxxxxxxxx/config)
> compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
> reproduce: (https://download.01.org/0day-ci/archive/20230703/202307030026.9sE2pk2x-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>
> | Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> | Closes: https://lore.kernel.org/r/202307030026.9sE2pk2x-lkp@xxxxxxxxx/
>
> New smatch warnings:
> fs/namei.c:4875 vfs_rename() warn: variable dereferenced before check 'source' (see line 4830)

Yeah, the check for source being non-NULL in:

if (source)
inode_unlock(source);

is pointless. When we are renaming something, we are guaranteed "something"
exists ;). I'll send a cleanup patch.

Honza

>
> vim +/source +4875 fs/namei.c
>
> 9fe61450972d39 Christian Brauner 2021-01-21 4752 int vfs_rename(struct renamedata *rd)
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4753 {
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4754 int error;
> 9fe61450972d39 Christian Brauner 2021-01-21 4755 struct inode *old_dir = rd->old_dir, *new_dir = rd->new_dir;
> 9fe61450972d39 Christian Brauner 2021-01-21 4756 struct dentry *old_dentry = rd->old_dentry;
> 9fe61450972d39 Christian Brauner 2021-01-21 4757 struct dentry *new_dentry = rd->new_dentry;
> 9fe61450972d39 Christian Brauner 2021-01-21 4758 struct inode **delegated_inode = rd->delegated_inode;
> 9fe61450972d39 Christian Brauner 2021-01-21 4759 unsigned int flags = rd->flags;
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4760 bool is_dir = d_is_dir(old_dentry);
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4761 struct inode *source = old_dentry->d_inode;
> 9055cba711891a Sage Weil 2011-05-24 4762 struct inode *target = new_dentry->d_inode;
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4763 bool new_is_dir = false;
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4764 unsigned max_links = new_dir->i_sb->s_max_links;
> 49d31c2f389acf Al Viro 2017-07-07 4765 struct name_snapshot old_name;
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4766
> 8d3e2936375bac Miklos Szeredi 2016-12-16 4767 if (source == target)
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4768 return 0;
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4769
> 4609e1f18e19c3 Christian Brauner 2023-01-13 4770 error = may_delete(rd->old_mnt_idmap, old_dir, old_dentry, is_dir);
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4771 if (error)
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4772 return error;
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4773
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4774 if (!target) {
> 4609e1f18e19c3 Christian Brauner 2023-01-13 4775 error = may_create(rd->new_mnt_idmap, new_dir, new_dentry);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4776 } else {
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4777 new_is_dir = d_is_dir(new_dentry);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4778
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4779 if (!(flags & RENAME_EXCHANGE))
> 4609e1f18e19c3 Christian Brauner 2023-01-13 4780 error = may_delete(rd->new_mnt_idmap, new_dir,
> 6521f891708292 Christian Brauner 2021-01-21 4781 new_dentry, is_dir);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4782 else
> 4609e1f18e19c3 Christian Brauner 2023-01-13 4783 error = may_delete(rd->new_mnt_idmap, new_dir,
> 6521f891708292 Christian Brauner 2021-01-21 4784 new_dentry, new_is_dir);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4785 }
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4786 if (error)
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4787 return error;
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4788
> 2773bf00aeb9bf Miklos Szeredi 2016-09-27 4789 if (!old_dir->i_op->rename)
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4790 return -EPERM;
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4791
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4792 /*
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4793 * If we are going to change the parent - check write permissions,
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4794 * we'll need to flip '..'.
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4795 */
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4796 if (new_dir != old_dir) {
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4797 if (is_dir) {
> 4609e1f18e19c3 Christian Brauner 2023-01-13 4798 error = inode_permission(rd->old_mnt_idmap, source,
> 47291baa8ddfda Christian Brauner 2021-01-21 4799 MAY_WRITE);
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4800 if (error)
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4801 return error;
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4802 }
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4803 if ((flags & RENAME_EXCHANGE) && new_is_dir) {
> 4609e1f18e19c3 Christian Brauner 2023-01-13 4804 error = inode_permission(rd->new_mnt_idmap, target,
> 47291baa8ddfda Christian Brauner 2021-01-21 4805 MAY_WRITE);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4806 if (error)
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4807 return error;
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4808 }
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4809 }
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4810
> 0b3974eb04c487 Miklos Szeredi 2014-04-01 4811 error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry,
> 0b3974eb04c487 Miklos Szeredi 2014-04-01 4812 flags);
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4813 if (error)
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4814 return error;
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4815
> 49d31c2f389acf Al Viro 2017-07-07 4816 take_dentry_name_snapshot(&old_name, old_dentry);
> 1d2ef590148300 Al Viro 2011-09-14 4817 dget(new_dentry);
> 28eceeda130f50 Jan Kara 2023-06-01 4818 /*
> 28eceeda130f50 Jan Kara 2023-06-01 4819 * Lock all moved children. Moved directories may need to change parent
> 28eceeda130f50 Jan Kara 2023-06-01 4820 * pointer so they need the lock to prevent against concurrent
> 28eceeda130f50 Jan Kara 2023-06-01 4821 * directory changes moving parent pointer. For regular files we've
> 28eceeda130f50 Jan Kara 2023-06-01 4822 * historically always done this. The lockdep locking subclasses are
> 28eceeda130f50 Jan Kara 2023-06-01 4823 * somewhat arbitrary but RENAME_EXCHANGE in particular can swap
> 28eceeda130f50 Jan Kara 2023-06-01 4824 * regular files and directories so it's difficult to tell which
> 28eceeda130f50 Jan Kara 2023-06-01 4825 * subclasses to use.
> 28eceeda130f50 Jan Kara 2023-06-01 4826 */
> 28eceeda130f50 Jan Kara 2023-06-01 4827 lock_two_inodes(source, target, I_MUTEX_NORMAL, I_MUTEX_NONDIR2);
> 9055cba711891a Sage Weil 2011-05-24 4828
> 51cc3a6620a6ca Hugh Dickins 2021-09-02 4829 error = -EPERM;
> 51cc3a6620a6ca Hugh Dickins 2021-09-02 @4830 if (IS_SWAPFILE(source) || (target && IS_SWAPFILE(target)))
> ^^^^^^
> Dereferenced.
>
> 51cc3a6620a6ca Hugh Dickins 2021-09-02 4831 goto out;
> ^^^^^^^^
> 51cc3a6620a6ca Hugh Dickins 2021-09-02 4832
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4833 error = -EBUSY;
> 7af1364ffa64db Eric W. Biederman 2013-10-04 4834 if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
> 9055cba711891a Sage Weil 2011-05-24 4835 goto out;
> 9055cba711891a Sage Weil 2011-05-24 4836
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4837 if (max_links && new_dir != old_dir) {
> 8de52778798fe3 Al Viro 2012-02-06 4838 error = -EMLINK;
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4839 if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
> 8de52778798fe3 Al Viro 2012-02-06 4840 goto out;
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4841 if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4842 old_dir->i_nlink >= max_links)
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4843 goto out;
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4844 }
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4845 if (!is_dir) {
> 8e6d782cab5088 J. Bruce Fields 2011-09-20 4846 error = try_break_deleg(source, delegated_inode);
> 8e6d782cab5088 J. Bruce Fields 2011-09-20 4847 if (error)
> 8e6d782cab5088 J. Bruce Fields 2011-09-20 4848 goto out;
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4849 }
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4850 if (target && !new_is_dir) {
> 8e6d782cab5088 J. Bruce Fields 2011-09-20 4851 error = try_break_deleg(target, delegated_inode);
> 8e6d782cab5088 J. Bruce Fields 2011-09-20 4852 if (error)
> 8e6d782cab5088 J. Bruce Fields 2011-09-20 4853 goto out;
> 8e6d782cab5088 J. Bruce Fields 2011-09-20 4854 }
> e18275ae55e07a Christian Brauner 2023-01-13 4855 error = old_dir->i_op->rename(rd->new_mnt_idmap, old_dir, old_dentry,
> 520c8b16505236 Miklos Szeredi 2014-04-01 4856 new_dir, new_dentry, flags);
> 51892bbb57e878 Sage Weil 2011-05-24 4857 if (error)
> 51892bbb57e878 Sage Weil 2011-05-24 4858 goto out;
> 51892bbb57e878 Sage Weil 2011-05-24 4859
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4860 if (!(flags & RENAME_EXCHANGE) && target) {
> 8767712f26d18a Al Viro 2018-05-27 4861 if (is_dir) {
> 8767712f26d18a Al Viro 2018-05-27 4862 shrink_dcache_parent(new_dentry);
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4863 target->i_flags |= S_DEAD;
> 8767712f26d18a Al Viro 2018-05-27 4864 }
> d83c49f3e36cec Al Viro 2010-04-30 4865 dont_mount(new_dentry);
> 8ed936b5671bfb Eric W. Biederman 2013-10-01 4866 detach_mounts(new_dentry);
> bc27027a73e8b8 Miklos Szeredi 2014-04-01 4867 }
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4868 if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4869 if (!(flags & RENAME_EXCHANGE))
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4870 d_move(old_dentry, new_dentry);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4871 else
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4872 d_exchange(old_dentry, new_dentry);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4873 }
> 51892bbb57e878 Sage Weil 2011-05-24 4874 out:
> 28eceeda130f50 Jan Kara 2023-06-01 @4875 if (source)
> ^^^^^^
> This check could be removed.
>
> 28eceeda130f50 Jan Kara 2023-06-01 4876 inode_unlock(source);
> 28eceeda130f50 Jan Kara 2023-06-01 4877 if (target)
> 5955102c9984fa Al Viro 2016-01-22 4878 inode_unlock(target);
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4879 dput(new_dentry);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4880 if (!error) {
> f4ec3a3d43bcdc Al Viro 2019-04-26 4881 fsnotify_move(old_dir, new_dir, &old_name.name, is_dir,
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4882 !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4883 if (flags & RENAME_EXCHANGE) {
> f4ec3a3d43bcdc Al Viro 2019-04-26 4884 fsnotify_move(new_dir, old_dir, &old_dentry->d_name,
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4885 new_is_dir, NULL, new_dentry);
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4886 }
> da1ce0670c14d8 Miklos Szeredi 2014-04-01 4887 }
> 49d31c2f389acf Al Viro 2017-07-07 4888 release_dentry_name_snapshot(&old_name);
> 0eeca28300df11 Robert Love 2005-07-12 4889
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4890 return error;
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 4891 }
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

Next message: Liu, Jingqi: "Re: [PATCH 0/5] iommu/vt-d: debugfs: Enhancements to IOMMU debugfs"
Previous message: Jonathan Corbet: "Re: [PATCH v1] Fix documentation of panic_on_warn"
In reply to: Dan Carpenter: "fs/namei.c:4875 vfs_rename() warn: variable dereferenced before check 'source' (see line 4830)"
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