[Devel] [PATCH] ext4: release leaked posix acl in ext4_xattr_set_acl

[Dmitry Monakhov]

Stanislav Kinsburskiy <skinsbursky at virtuozzo.com> writes:

> Posix acl is used to convert of an extended attribute, provided by user to
> ext4 attributes. In particular to I-mode in case of ACL_TYPE_ACCESS request.
> IOW, this object is allocated, used for convertion, not stored anywhere and
> must be freed.
> However posix_acl_update_mode() can zerofy the pointer to support
> ext4_set_acl() logic, but then the object is leaked.
> So, fix it by releasing new temporary pointer with the same value instead of
> acl pointer.
So you are telling me that:
ext4_xattr_set_acl
L1 acl = posix_acl_from_xattr 
L2 -> ext4_set_acl(handle, inode, type, acl)
L3    ->posix_acl_update_mode(inode, &inode->i_mode, &acl)
      *acl = NULL;
      You are saying that instruction above can affect value at L1?
      HOW? acl passed to ext4_set_acl() by value, so
      posix_acl_update_mode() can affect value only in L2 and L3 but not L1. 

Stas, have you drunk a lousy beer today?
>
> https://jira.sw.ru/browse/PSBM-81384
>
> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
> ---
>  fs/ext4/acl.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c
> index 917e819..2640d7b 100644
> --- a/fs/ext4/acl.c
> +++ b/fs/ext4/acl.c
> @@ -403,7 +403,7 @@ ext4_xattr_set_acl(struct dentry *dentry, const char *name, const void *value,
>  {
>  	struct inode *inode = dentry->d_inode;
>  	handle_t *handle;
> -	struct posix_acl *acl;
> +	struct posix_acl *acl, *tmp;
>  	int error, retries = 0;
>  	int update_mode = 0;
>  	umode_t mode = inode->i_mode;
> @@ -416,7 +416,7 @@ ext4_xattr_set_acl(struct dentry *dentry, const char *name, const void *value,
>  		return -EPERM;
>  
>  	if (value) {
> -		acl = posix_acl_from_xattr(&init_user_ns, value, size);
> +		acl = tmp = posix_acl_from_xattr(&init_user_ns, value, size);
>  		if (IS_ERR(acl))
>  			return PTR_ERR(acl);
>  		else if (acl) {
> @@ -425,7 +425,7 @@ ext4_xattr_set_acl(struct dentry *dentry, const char *name, const void *value,
>  				goto release_and_out;
>  		}
>  	} else
> -		acl = NULL;
> +		acl = tmp = NULL;
>  
>  retry:
>  	handle = ext4_journal_start(inode, EXT4_HT_XATTR,
> @@ -452,7 +452,7 @@ ext4_xattr_set_acl(struct dentry *dentry, const char *name, const void *value,
>  		goto retry;
>  
>  release_and_out:
> -	posix_acl_release(acl);
> +	posix_acl_release(tmp);
>  	return error;
>  }
>  
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