In D26243#587330, @asomers wrote:

Isn't audit_nfsarg_vnode1 the problem? You already know the path when you call AUDIT_ARG_UPATH1_VP, right?

In D26243#587174, @shivank wrote:

In D26243#587132, @mjg wrote:

Audit support for regular lookup starts with AUDIT_ARG_UPATH1_VP/AUDIT_ARG_UPATH2_VP without any vnodes locked. Later on visited vnodes get added with AUDIT_ARG_VNODE1/AUDIT_ARG_VNODE2 which only performs VOP_GETATTR (i.e. does *NOT* resolve any paths). Your code should follow the same scheme.

As you can see path resolving routines can take vnode locks on their own (modulo the smr case). This means they can't be called with locked vnodes to begin with, as otherwise you risk violating global lock ordering and consequently deadlocking the kernel.

The VOP_ISLOCKED routine is not entirely legal to call if you don't hold the lock. The name is perhaps misleading, but it can only reliably tell you that you have an exclusive lock or that *SOMEONE* has a shared lock (and it may be you). Or to put it differently, if you don't have the vnode locked but someone else has it shared locked, you will get non-0 and that's how you get the panic. Regardless of this problem, adding the call reduces performance and most notably suggests a bug on its own.

So the question is why are you calling here with any vnodes locked.

I wish to audit the canonical path of the file requested by the NFS clients. The requested path from the client is extracted in the NFS server using nfsrv_parsename, but the vnode is locked in some NFS services. I thought of unlocking/relocking of vnode for path audit but Rick advised not to. That's why I had to call this locked vnode.

Thanks for your question which made me rethink the problem from scratch and I got a new idea for auditing path.

Hi @rmacklem and @asomers, if I use nfsvno_namei to get the canonical path for the client, I will not the need the AUDIT_ARG_UPATH1_VP.which will save me from all the trouble of passing locked vnode to vn_fullpath_global. Please provide your opinion on the same.

In D26243#587132, @mjg wrote:

Audit support for regular lookup starts with AUDIT_ARG_UPATH1_VP/AUDIT_ARG_UPATH2_VP without any vnodes locked. Later on visited vnodes get added with AUDIT_ARG_VNODE1/AUDIT_ARG_VNODE2 which only performs VOP_GETATTR (i.e. does *NOT* resolve any paths). Your code should follow the same scheme.

As you can see path resolving routines can take vnode locks on their own (modulo the smr case). This means they can't be called with locked vnodes to begin with, as otherwise you risk violating global lock ordering and consequently deadlocking the kernel.

The VOP_ISLOCKED routine is not entirely legal to call if you don't hold the lock. The name is perhaps misleading, but it can only reliably tell you that you have an exclusive lock or that *SOMEONE* has a shared lock (and it may be you). Or to put it differently, if you don't have the vnode locked but someone else has it shared locked, you will get non-0 and that's how you get the panic. Regardless of this problem, adding the call reduces performance and most notably suggests a bug on its own.

So the question is why are you calling here with any vnodes locked.

Audit support for regular lookup starts with AUDIT_ARG_UPATH1_VP/AUDIT_ARG_UPATH2_VP without any vnodes locked. Later on visited vnodes get added with AUDIT_ARG_VNODE1/AUDIT_ARG_VNODE2 which only performs VOP_GETATTR (i.e. does *NOT* resolve any paths). Your code should follow the same scheme.

I feel vfs_cache.c changes for making vn_fullpath_global work for optionally locked vnode are causing the trouble. Though I'm not sure what's the problem. I request Mateusz Guzik, @mjg to have a look at my vfs_cache.c changes. I would be grateful for your time.

The new code looks better. But grrr, there are two big problems:

1. It doesn't compile due to some recent changes on head. I suggest the following:
   • Remove the <rpc/rpc.h>, <sys/mount.h>, and <fs/nfs/*> includes from audit.h. In addition to fixing the compile failure, it's generally not recommended to include headers from other headers. Sometimes it's necessary, but it also causes header pollution, and slow build times. Instead of including those files, just forward declare struct nfsrv_descript; and struct kaudit_record;.
   • Add `<netinet/in.h>, <rpc/rpc.h>, <fs/nfs/nfsdport.h>, <fs/nfs/nfsproto.h>, and <fs/nfs/nfs.h> to audit_bsm_db.c
   • Add <rpc/rpc.h>, <fs/nfs/nfsport.h>, <fs/nfs/nfsproto.h>, and <fs/nfs/nfs.h> to audit.c

• merge vn_fullpath_any and vn_vptocnp with their locked counterpart to work for optionally locked vnodes.

I created a new review - D26243. Sorry for the trouble.

It was earlier being reviewed on D25869. But due to change of base revision, It was showing changes which were not mine. So, I created a new review here.

In D25869#583083, @shivank wrote:

It looks like your most recent change rebased the base revision. That makes it very hard to see which changes are from you and which aren't. Could you please either un-rebase it or, if that's not possible, open a new review?

Ohh, Sorry! I didn't thought pulling HEAD changes will create this side-effect in revision
I think I would open a new review as going back will have conflicting changes again. Should I abandon this while creating a new one??

It looks like your most recent change rebased the base revision. That makes it very hard to see which changes are from you and which aren't. Could you please either un-rebase it or, if that's not possible, open a new review?

Using two completely separate functions reduces the scope of error. Also prevent any mutation to the current code path for not locked vnodes, while allowing it to work for locked vnodes.

• updated sys/kern/vfs_cache.c to reduce code duplication with vn_fullpath_dir
• some trivial changes

Regarding code duplication in vn_fullpath_dir_locked:
I modified vn_fullpath_dir(and removed vn_fullpath_dir_locked) for optionally locked vnode here in git commit: https://github.com/shivankgarg98/freebsd/commit/418c1c2a6de9989fe7a541f6111ee2c3f2786c7b
It works fine NFSv4=3 case but somehow breaks nfsrvd_open to result in an error.{and hence can't open/create a regular file from client}.
Using two completely separate functions reduces the scope of error. Also prevent any mutation to the current code path for not locked vnodes, while allowing it to work for locked vnodes.

follow-up on suggested changes.

This is a much better locking strategy. However, there's a lot of duplicated code. Could you maybe combine the _locked with the original functions, so there wouldn't be so much duplication?

removing unlocking/relocking implementation for vnode for auditing path, instead, define separate functions in vfs_cache.c for locked vnode as argument.

Thanks for all suggestions. I have incorporated them into my code. There is just a directory vnode unlocking/relocking issue not done yet.

In summary, locking and unlocking vnodes in this code is dangerous
and I am not in a position to make sure what you do is safe.

follow up on changes suggested by asomers@