On Tue, Feb 28, 2017 at 10:37 PM, Richard Guy Briggs <r...@redhat.com> wrote: > Sorry, I forgot to include Cc: in this cover letter for context to the 4 > alt patches. > > On 2017-02-28 22:15, Richard Guy Briggs wrote: >> The background to this is: >> https://github.com/linux-audit/audit-kernel/issues/8 >> >> In short, audit SYSCALL records for *init_module were occasionally >> accompanied by hundreds to thousands of null PATH records. >> >> I chatted with Al Viro and Eric Paris about this Friday afternoon and >> they seemed to vaguely recall this issue and didn't have any solid >> recommendations as to what was the right thing to do (other than the >> same suggestion from both that I won't print here). >> >> It was reproducible on a number of vintages of distributions with >> default kernels, but triggering on very few of the many modules loaded >> at boot time. It was reproduced with fs-nfs4 and nfsv4 modules on >> tracefs, but there are reports of it also happening with debugfs. It >> was triggering only in __audit_inode_child with a parent that was not >> found in the task context's audit names_list.
I'm no expert on the tracing system, but my understanding is that it used to use debugfs but now prefers tracefs so perhaps depending on the vintage of the kernel/userspace you will see it on either debugfs or tracefs. I'm also guessing that module load order may have an effect, maybe not. >> I have four potential solutions listed in my order of preference and I'd >> like to get some feedback about which one would be the most acceptable. >From an audit perspective, I'm generally not a fan of throwing away information, especially since solution #4 seems to provide some basic PATH information. Although I guess the issue is do we care about tracefs/debugfs PATH records? >> 1 - In __audit_inode_child, return immedialy upon detecting TRACEFS and >> DEBUGFS (and potentially other filesystems identified, via s_magic). If we decide we want to ignore debugfs/tracefs this may be the best solution. >> 2 - In __audit_inode_child, return after not finding the parent in that >> task context's audit names_list. This doesn't seem like the right answer. >> 3 - In __audit_inode_child, mark the parent and its child as "hidden" >> when the parent isn't found in that task context's audit names_list. >> This will still result in an "items=" count that does not match the >> number of accompanying PATH records for that SYSCALL record, which >> may upset userspace tools but would still indicate suppressed >> records. Similar to door #2, this doesn't seem right to me. >> 4 - In __audit_inode_child, when the parent isn't found, store the >> child's dentry in the child's (new or not) audit_names structure >> (properly refcounted with dget) and store the parent's dentry in its >> newly created audit_names structure (via dget_parent), then if the >> name isn't available at PATH record generation time, use that stored >> value (with dentry_path_raw and released with dput) This seems most in keeping with the spirit of audit. >> Is there another more elegant solution that I've missed that catches >> things before they get anywhere near audit_inode_child (called from >> tracefs' notifiers)? >> >> I'll thread onto this message tested patches for all four solutions. >> >> - RGB >> >> -- >> Richard Guy Briggs <r...@redhat.com> >> Kernel Security Engineering, Base Operating Systems, Red Hat >> Remote, Ottawa, Canada >> Voice: +1.647.777.2635, Internal: (81) 32635 -- paul moore www.paul-moore.com