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

[Oleksandr Natalenko <oleksandr@natalenko.name>]

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>
> 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);

Do we need to do this as well:

#include <linux/kmemleak.h>

?

Because otherwise for 5.9 I get:

[  148s] fs/efivarfs/inode.c: In function 'efivarfs_create':
[  148s] fs/efivarfs/inode.c:106:2: error: implicit declaration of 
function 'kmemleak_ignore' [-Werror=implicit-function-declaration]
[  148s]   106 |  kmemleak_ignore(var);
[  148s]       |  ^~~~~~~~~~~~~~~

> 
>  	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)