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

On 02/20/2012 06:12 PM, Lennart Poettering wrote:
On Wed, 15.02.12 14:23, Roberto Sassu (roberto.sassu@xxxxxxxxx) 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

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.


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;
+       /* Mount the securityfs filesystem */
+       mount_setup_early();
+       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.


+       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).


Roberto Sassu

Otherwise looks good.


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