virt-aa-helper: Avoid duplicate when append rule

when a device is dynamically attached to a VM, and it needs a special
system access for apparmor, libvirt calls virt-aa-helper (with argument -F)
to append a new rule to the apparmor profile of the VM. virt-aa-helper does
not check for duplicate and blindly appends the rule to the profile. since
there is no rule removal when a device is detached, this can make the profile
grow in size if a big number of attach/detach operations are done and the
profile might hit the size limit and futur attach operations might dysfunction
because no rule can be added into the apparmor profile.

this patch tries to mitigate this issue by doing a duplicate check
when rules are appended into the profile. this fix does not guarantee
the absence of duplicates but should be enough to prevent the profile
to grow significantly in size and reach its size limit.

Signed-off-by: Hector CAO <hector.cao@canonical.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c
index b662d971cb7b1c0c1d6273ed16781c7e42d80aea..8a297d4b54221c34b14b86c88bd664e2e79664ea 100644 (file)
--- a/src/security/virt-aa-helper.c
+++ b/src/security/virt-aa-helper.c
@@ -208,10 +208,21 @@ update_include_file(const char *include_file, const char *included_files,
             return -1;
     }
 
-    if (append && virFileExists(include_file))
+    if (append && existing) {
+        /* Duplicate check: include_files might contain multiple rules
+         * the best is to check for each rule (separated by \n) but
+         * it might be overkilled, just do the check for the whole
+         * include_files.
+         * Most of the time, include_files contains only one rule
+         * so this check is OK to avoid the overflow of the profile
+         * duplicates might still exist though.
+         */
+        if (strstr(existing, included_files) != NULL)
+            return 0;
         pcontent = g_strdup_printf("%s%s", existing, included_files);
-    else
+    } else {
         pcontent = g_strdup_printf("%s%s", warning, included_files);
+    }
 
     plen = strlen(pcontent);
     if (plen > MAX_FILE_LEN) {