linux-kernel - Re: [PATCH v3] ima: Fix NULL pointer dereference in ima_file

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Date:   Wed, 16 Sep 2020 18:51:49 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     KP Singh <kpsingh@...omium.org>, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org
Cc:     Florent Revest <revest@...omium.org>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v3] ima: Fix NULL pointer dereference in ima_file_hash

On Wed, 2020-09-16 at 18:02 +0000, KP Singh wrote:
> From: KP Singh <kpsingh@...gle.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@...gle.com>
> Reviewed-by: Florent Revest <revest@...omium.org>

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

Mimi