[PATCH v3] ima: Fix NULL pointer dereference in ima_file_hash

[Mimi Zohar]

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

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

Mimi