Re: [PATCH] efivarfs: revert "fix memory leak in efivarfs_create()"

Re: [PATCH] efivarfs: revert "fix memory leak in efivarfs_create()"

[Oleksandr Natalenko]

Hello.

On 25.11.2020 08:53, Ard Biesheuvel wrote:
> The memory leak addressed by commit fe5186cf12e3 is a false positive:
> all allocations are recorded in a linked list, and freed when the
> filesystem is unmounted. This leads to double frees, and as reported
> by David, leads to crashes if SLUB is configured to self destruct when
> double frees occur.
> 
> So drop the redundant kfree() again, and instead, mark the offending
> pointer variable so the allocation is ignored by kmemleak.
> 
> Cc: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@gmail.com>

Should also have:

Cc: <stable@vger.kernel.org> # v5.9

> Fixes: fe5186cf12e3 ("efivarfs: fix memory leak in efivarfs_create()")
> Reported-by: David Laight <David.Laight@aculab.com>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  fs/efivarfs/inode.c | 1 +
>  fs/efivarfs/super.c | 1 -
>  2 files changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
> index 96c0c86f3fff..38324427a2b3 100644
> --- a/fs/efivarfs/inode.c
> +++ b/fs/efivarfs/inode.c
> @@ -103,6 +103,7 @@ static int efivarfs_create(struct inode *dir,
> struct dentry *dentry,
>  	var->var.VariableName[i] = '\0';
> 
>  	inode->i_private = var;
> +	kmemleak_ignore(var);
> 
>  	err = efivar_entry_add(var, &efivarfs_list);
>  	if (err)
> diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
> index f943fd0b0699..15880a68faad 100644
> --- a/fs/efivarfs/super.c
> +++ b/fs/efivarfs/super.c
> @@ -21,7 +21,6 @@ LIST_HEAD(efivarfs_list);
>  static void efivarfs_evict_inode(struct inode *inode)
>  {
>  	clear_inode(inode);
> -	kfree(inode->i_private);
>  }
> 
>  static const struct super_operations efivarfs_ops = {

-- 
   Oleksandr Natalenko (post-factum)

Re: [PATCH] efivarfs: revert "fix memory leak in efivarfs_create()"

[Ard Biesheuvel]

On Wed, 25 Nov 2020 at 09:05, Oleksandr Natalenko
<oleksandr@natalenko.name> wrote:
>
> Hello.
>
> On 25.11.2020 08:53, Ard Biesheuvel wrote:
> > The memory leak addressed by commit fe5186cf12e3 is a false positive:
> > all allocations are recorded in a linked list, and freed when the
> > filesystem is unmounted. This leads to double frees, and as reported
> > by David, leads to crashes if SLUB is configured to self destruct when
> > double frees occur.
> >
> > So drop the redundant kfree() again, and instead, mark the offending
> > pointer variable so the allocation is ignored by kmemleak.
> >
> > Cc: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@gmail.com>
>
> Should also have:
>
> Cc: <stable@vger.kernel.org> # v5.9
>

No it should not. The fixes tag should be sufficient.

> > Fixes: fe5186cf12e3 ("efivarfs: fix memory leak in efivarfs_create()")
> > Reported-by: David Laight <David.Laight@aculab.com>
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >  fs/efivarfs/inode.c | 1 +
> >  fs/efivarfs/super.c | 1 -
> >  2 files changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
> > index 96c0c86f3fff..38324427a2b3 100644
> > --- a/fs/efivarfs/inode.c
> > +++ b/fs/efivarfs/inode.c
> > @@ -103,6 +103,7 @@ static int efivarfs_create(struct inode *dir,
> > struct dentry *dentry,
> >       var->var.VariableName[i] = '\0';
> >
> >       inode->i_private = var;
> > +     kmemleak_ignore(var);
> >
> >       err = efivar_entry_add(var, &efivarfs_list);
> >       if (err)
> > diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
> > index f943fd0b0699..15880a68faad 100644
> > --- a/fs/efivarfs/super.c
> > +++ b/fs/efivarfs/super.c
> > @@ -21,7 +21,6 @@ LIST_HEAD(efivarfs_list);
> >  static void efivarfs_evict_inode(struct inode *inode)
> >  {
> >       clear_inode(inode);
> > -     kfree(inode->i_private);
> >  }
> >
> >  static const struct super_operations efivarfs_ops = {
>
> --
>    Oleksandr Natalenko (post-factum)

Re: [PATCH] efivarfs: revert "fix memory leak in efivarfs_create()"

[Greg Kroah-Hartman]

On Wed, Nov 25, 2020 at 09:05:42AM +0100, Ard Biesheuvel wrote:
> On Wed, 25 Nov 2020 at 09:05, Oleksandr Natalenko
> <oleksandr@natalenko.name> wrote:
> >
> > Hello.
> >
> > On 25.11.2020 08:53, Ard Biesheuvel wrote:
> > > The memory leak addressed by commit fe5186cf12e3 is a false positive:
> > > all allocations are recorded in a linked list, and freed when the
> > > filesystem is unmounted. This leads to double frees, and as reported
> > > by David, leads to crashes if SLUB is configured to self destruct when
> > > double frees occur.
> > >
> > > So drop the redundant kfree() again, and instead, mark the offending
> > > pointer variable so the allocation is ignored by kmemleak.
> > >
> > > Cc: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@gmail.com>
> >
> > Should also have:
> >
> > Cc: <stable@vger.kernel.org> # v5.9
> >
> 
> No it should not. The fixes tag should be sufficient.

No, "Fixes:" does not ever mean "I want this patch to go to a stable
tree".  It might happen, it might not, if you REALLY know this should go
to a stable tree, please follow the directions for what we have been
doing for 15+ years now, as documented in:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

Hint, use "cc: stable@vger.kernel.org" if you know you want it applied,
otherwise it's just a best-guess-effort on our part.

thanks,

greg k-h