2022-06-30 04:06:29

by Katrin Jo

Subject: [PATCH] kernfs: fix potential NULL dereference in __kernfs_remove

From: katrinzhou <[email protected]>

When lockdep is enabled, lockdep_assert_held_write would
cause potential NULL pointer dereference.

Fix the folloeing smatch warnings:

fs/kernfs/dir.c:1353 __kernfs_remove() warn: variable dereferenced before check 'kn' (see line 1346)

Signed-off-by: katrinzhou <[email protected]>
---
fs/kernfs/dir.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 6eca72cfa1f2..1cc88ba6de90 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1343,14 +1343,17 @@ static void __kernfs_remove(struct kernfs_node *kn)
{
struct kernfs_node *pos;

+ /* Short-circuit if non-root @kn has already finished removal. */
+ if (!kn)
+ return;
+
lockdep_assert_held_write(&kernfs_root(kn)->kernfs_rwsem);

/*
- * Short-circuit if non-root @kn has already finished removal.
* This is for kernfs_remove_self() which plays with active ref
* after removal.
*/
- if (!kn || (kn->parent && RB_EMPTY_NODE(&kn->rb)))
+ if (kn->parent && RB_EMPTY_NODE(&kn->rb))
return;

pr_debug("kernfs %s: removing\n", kn->name);
--
2.27.0

2022-06-30 08:08:52

by Greg Kroah-Hartman

Subject: Re: [PATCH] kernfs: fix potential NULL dereference in __kernfs_remove

On Thu, Jun 30, 2022 at 12:00:47PM +0800, [email protected] wrote:
> From: katrinzhou <[email protected]>
>
> When lockdep is enabled, lockdep_assert_held_write would
> cause potential NULL pointer dereference.
>
> Fix the folloeing smatch warnings:
>
> fs/kernfs/dir.c:1353 __kernfs_remove() warn: variable dereferenced before check 'kn' (see line 1346)
>
> Signed-off-by: katrinzhou <[email protected]>

Can you please submit this with your legal name that you use to sign
documents?

Also, what commit id does this fix? Did you actually hit this with a
real workload? How can this be reproduced and tested?

thanks,

greg k-h

2022-06-30 08:21:03

by Katrin Jo

Subject: Re: [PATCH] kernfs: fix potential NULL dereference in __kernfs_remove

On Thu, Jun 30, 2022 at 3:28 PM Greg KH <[email protected]> wrote:
>
> On Thu, Jun 30, 2022 at 12:00:47PM +0800, [email protected] wrote:
> > From: katrinzhou <[email protected]>
> >
> > When lockdep is enabled, lockdep_assert_held_write would
> > cause potential NULL pointer dereference.
> >
> > Fix the folloeing smatch warnings:
> >
> > fs/kernfs/dir.c:1353 __kernfs_remove() warn: variable dereferenced before check 'kn' (see line 1346)
> >
> > Signed-off-by: katrinzhou <[email protected]>
>
> Can you please submit this with your legal name that you use to sign
> documents?
>
> Also, what commit id does this fix? Did you actually hit this with a
> real workload? How can this be reproduced and tested?
>
> thanks,
>
> greg k-h

Sorry for the formatting issue. I'll submit a new patch soon.
This problem is found via static code analysis, and by now
I have not reproduced / tested it.

Best regards,
Katrin