Re: [systemd-devel] [PATCH 2/2] main: added support for loading IMA custom policies

[Roberto Sassu <roberto.sassu@polito.it>]

On 02/20/2012 06:12 PM, Lennart Poettering wrote:
> On Wed, 15.02.12 14:23, Roberto Sassu (roberto.sassu@polito.it) wrote:
>
>> The new function ima_setup() loads an IMA custom policy from a file in the
>> default location '/etc/sysconfig/ima-policy', if present, and writes it to
>> the path 'ima/policy' in the security filesystem. This function is executed
>> at early stage in order to avoid that some file operations are not measured
>> by IMA and it is placed after the initialization of SELinux because IMA
>> needs the latter (or other security modules) to understand LSM-specific
>> rules.
>
> This must be a configure option. I am pretty sure most embedded people
> don't require this feature.
>
> The kernel side of things is merged upstream I presume? (We generally
> only want to support stuff in our code that is merged upstream itself)
>

Yes. IMA was in the mainline kernel since 2.6.30.


>> +#define IMA_SECFS_DIR SECURITYFS_MNTPOINT "/ima"
>> +#define IMA_SECFS_POLICY IMA_SECFS_DIR "/policy"
>
> Please use proper strings for this. (see my earlier mail)
>

Ok, i will replace the former with the hard-coded pathname.


>> +#define IMA_POLICY_PATH "/etc/sysconfig/ima-policy"
>
> This is a Fedoraism. Please introduce a proper configuration file for this.
>

Ok, i will answer about this in the next your email.


>> +
>> +int ima_setup(void) {
>> +       struct stat st;
>> +       ssize_t policy_size = 0, written = 0;
>> +       char *policy;
>> +       int policyfd = -1, imafd = -1;
>> +       int result = 0;
>> +
>> +#ifndef HAVE_SELINUX
>> +       /* Mount the securityfs filesystem */
>> +       mount_setup_early();
>> +#endif
>> +
>> +       if (stat(IMA_POLICY_PATH,&st) == -1)
>> +               return 0;
>
> We tend to do "<  0" instead of "== -1" checks for syscall
> failures. Might be good to use the same here, but this is not necessary
> for getting this merged.
>

Ok.


>> +
>> +       policyfd = open(IMA_POLICY_PATH, O_RDONLY);
>
> We tend to add O_CLOEXEC to all fds we open, just for being
> paranoid. Please do so here, too, to avoid surprise and avoid exceptions
> when people grep for all open() invocations looking for O_CLOEXEC.
>

No problem, i will do the change.


>> +       if (policyfd<  0) {
>> +               log_error("Failed to open the IMA custom policy file %s (%s), "
>> +                         "ignoring.", IMA_POLICY_PATH, strerror(errno));
>> +               return 0;
>> +       }
>
> Consider using %m instead of %s and strerror(errno).
>
>> +       imafd = open(IMA_SECFS_POLICY, O_WRONLY);
>
> Also O_CLOEXEC please.
>
>> +       if (imafd<  0) {
>> +               log_error("Failed to open the IMA kernel interface %s (%s), "
>> +                         "ignoring.", IMA_SECFS_POLICY, strerror(errno));
>> +               goto out;
>> +       }
>> +
>> +       policy = mmap(NULL, policy_size, PROT_READ, MAP_PRIVATE, policyfd, 0);
>> +       if (policy == NULL) {
>
> mmap() returns MAP_FAILED (i.e. (void) -1) on failure, not NULL. This
> check needs to be fixed.
>

Ok, i will replace NULL with MAP_FAILED.


>> +               log_error("mmap() failed (%s), freezing", strerror(errno));
>> +               result = -errno;
>> +               goto out;
>> +       }
>> +
>> +       while(written<  policy_size) {
>> +               ssize_t len = write(imafd, policy + written,
>> +                                   policy_size - written);
>> +               if (len<= 0) {
>> +                         log_error("Failed to load the IMA custom policy "
>> +                                   "file %s (%s), ignoring.", IMA_POLICY_PATH,
>> +                                   strerror(errno));
>> +                         goto out_mmap;
>> +               }
>> +               written += len;
>> +       }
>
> It might make sense to use loop_write() here instead, which does more or
> less this loop, and is defined in util.c anyway.
>

I briefly looked at the code and i'm not sure to use it, because i want
to add some extra information in the output message (for example the
line number of the rule in the policy file that was rejected by IMA).

Thanks

Roberto Sassu


> Otherwise looks good.
>
> Lennart
>