Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <1e1177862e4465cadbb65ee3ad0adfae3f4ec92e.camel@linux.ibm.com>
Subject: Re: [PATCH v3] ima: Fix NULL pointer dereference in ima_file_hash
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     KP Singh <kpsingh@chromium.org>, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org
Cc:     Florent Revest <revest@chromium.org>,
        James Morris <jmorris@namei.org>,
        Kees Cook <keescook@chromium.org>,
        Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
        Jann Horn <jannh@google.com>
Date:   Wed, 16 Sep 2020 18:51:49 -0400
In-Reply-To: <20200916180242.430668-1-kpsingh@chromium.org>
References: <20200916180242.430668-1-kpsingh@chromium.org>
Content-Type: text/plain; charset="ISO-8859-15"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Wed, 2020-09-16 at 18:02 +0000, KP Singh wrote:
> From: KP Singh <kpsingh@google.com>
> 
> ima_file_hash can be called when there is no iint->ima_hash available
> even though the inode exists in the integrity cache. It is fairly
> common for a file to not have a hash. (e.g. an mknodat, prior to the
> file being closed).
> 
> Another example where this can happen (suggested by Jann Horn):
> 
> Process A does:
> 
> 	while(1) {
> 		unlink("/tmp/imafoo");
> 		fd = open("/tmp/imafoo", O_RDWR|O_CREAT|O_TRUNC, 0700);
> 		if (fd == -1) {
> 			perror("open");
> 			continue;
> 		}
> 		write(fd, "A", 1);
> 		close(fd);
> 	}
> 
> and Process B does:
> 
> 	while (1) {
> 		int fd = open("/tmp/imafoo", O_RDONLY);
> 		if (fd == -1)
> 			continue;
>     		char *mapping = mmap(NULL, 0x1000, PROT_READ|PROT_EXEC,
> 			 	     MAP_PRIVATE, fd, 0);
> 		if (mapping != MAP_FAILED)
> 			munmap(mapping, 0x1000);
> 		close(fd);
>   	}
> 
> Due to the race to get the iint->mutex between ima_file_hash and
> process_measurement iint->ima_hash could still be NULL.
> 
> Fixes: 6beea7afcc72 ("ima: add the ability to query the cached hash of a given file")
> Signed-off-by: KP Singh <kpsingh@google.com>
> Reviewed-by: Florent Revest <revest@chromium.org>

Thanks, the patch is queued in next-integrity-testing.

Mimi