[PATCH v2] security: commoncap: fix potential memleak on error path from vfs_getxattr_alloc

[Serge E. Hallyn]

On Tue, Oct 25, 2022 at 09:33:57PM +0800, Gaosheng Cui wrote:
> In cap_inode_getsecurity(), we will use vfs_getxattr_alloc() to
> complete the memory allocation of tmpbuf, if we have completed
> the memory allocation of tmpbuf, but failed to call handler->get(...),
> there will be a memleak in below logic:
> 
>   |-- ret = (int)vfs_getxattr_alloc(mnt_userns, ...)  <-- alloc for tmpbuf
>     |-- value = krealloc(*xattr_value, error + 1, flags)  <-- alloc memory
>     |-- error = handler->get(handler, ...)  <-- if error
>     |-- *xattr_value = value <-- xattr_value is &tmpbuf  <-- memory leak
> 
> So we will try to free(tmpbuf) after vfs_getxattr_alloc() fails to fix it.
> 
> Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities")

Acked-by: Serge Hallyn <serge at hallyn.com>

> Signed-off-by: Gaosheng Cui <cuigaosheng1 at huawei.com>
> ---
> v2:
> - Update the Fixes tag, from 71bc356f93a1 to 8db6c34f1dbc. Thanks!
>  security/commoncap.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 5fc8986c3c77..bc751fa5adad 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -401,8 +401,10 @@ int cap_inode_getsecurity(struct user_namespace *mnt_userns,
>  				      &tmpbuf, size, GFP_NOFS);
>  	dput(dentry);
>  
> -	if (ret < 0 || !tmpbuf)
> -		return ret;
> +	if (ret < 0 || !tmpbuf) {
> +		size = ret;
> +		goto out_free;
> +	}
>  
>  	fs_ns = inode->i_sb->s_user_ns;
>  	cap = (struct vfs_cap_data *) tmpbuf;
> -- 
> 2.25.1