Failure to set a watch on a non existing directory

Failure to set a watch on a non existing directory

[seth]

Hello,

I reported a behavior that seemed anormal to the auditd maintainer:

https://lists.linux-audit.osci.io/archives/list/linux-audit@lists.linux-audit.osci.io/thread/KOPL2QPINU6F6WVSKN7U3LRLVIXEQYLZ/

The behavior is the impossibility to make a watch on a directory with
`auditctl -F dir=$path` while it is possible with `auditctl -w $path`.

This is problematic as directories may not exists yet when auditd is
initialized (eg: from kernel command line), and the `-w` rules are
marked as deprecated by auditctl.

Here a few tests that illustrate the problem:

- nonexisting path

#+begin_src bash
auditctl -a always,exit -F arch=b64 -F path=/nonexisting_path -F perm=wa
auditctl -a always,exit -F path=/nonexisting_path -F perm=wa
auditctl -l
#+end_src

#+RESULTS:
: perm used without an arch is slower
: perm used without an arch is slower
: -a always,exit -F arch=b64 -S open,bind,truncate,ftruncate,rename,mkdir,rmdir,creat,link,unlink,symlink,chmod,fchmod,chown,fchown,lchown,mknod,acct,swapon,quotactl,setxattr,lsetxattr,fsetxattr,removexattr,lremovexattr,fremovexattr,openat,mkdirat,mknodat,fchownat,unlinkat,renameat,linkat,symlinkat,fchmodat,fallocate,renameat2,openat2 -F path=/nonexisting_path -F perm=wa
: -w /nonexisting_path -p wa

- nonexisting_dir

This will error:

#+begin_src bash
auditctl -a always,exit -F dir=/nonexisting_dir -F perm=wa -k nonexisting
#+end_src

#+RESULTS:
: perm used without an arch is slower
: perm used without an arch is slower
: Error sending add rule data request (No such file or directory)
: There was an error while processing parameters

#+begin_src bash
auditctl -a always,exit -F arch=b64 -F dir=/nonexisting_dir -F perm=wa -k nonexisting_dir
auditctl -l
#+end_src

#+RESULTS:
: Error sending add rule data request (No such file or directory)
: There was an error while processing parameters

Steve Grubb suggested that the issue may be to watch at /, but I don't think so:

#+begin_src bash
auditctl -a always,exit -F arch=b64 -F dir=/root/.config/nonexisting_dir -F perm=wa -k nonexisting_dir
#+end_src

#+RESULTS:
: Error sending add rule data request (No such file or directory)
: There was an error while processing parameters

This will not error:

#+begin_src bash
auditctl -w /root/.config/nonexisting_dir -F perm=wa -k nonexisting_dir
#+end_src

#+RESULTS:
: Old style watch rules are slower
: perm used without an arch is slower
: perm used without an arch is slower
: -w /root/.config/nonexisting_dir -p rwxa -p wa -k nonexisting_dir


Additionally here is quote from Steve Grubb about tracing the execution
of auditctl:

#+begin_quote
rule goes into the kernel:
sendto(4, [{nlmsg_len=1080, nlmsg_type=AUDIT_ADD_RULE, 
nlmsg_flags=NLM_F_REQUEST|NLM_F_ACK, nlmsg_seq=2, nlmsg_pid=0}, 
"\x04\x00\x00\x00\x02\x00\x00\x00\x03\x00\x00\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"...], 
1080, 0, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 12) = 1080

Answer back:
recvfrom(4, [{nlmsg_len=1100, nlmsg_type=NLMSG_ERROR, nlmsg_flags=0, 
nlmsg_seq=2, nlmsg_pid=270500}, {error=-ENOENT, msg=[{nlmsg_len=1080, 
nlmsg_type=AUDIT_ADD_RULE, nlmsg_flags=NLM_F_REQUEST|NLM_F_ACK, nlmsg_seq=2, 
nlmsg_pid=0}, 
"\x04\x00\x00\x00\x02\x00\x00\x00\x03\x00\x00\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"...]}], 
8988, MSG_PEEK|MSG_DONTWAIT, {sa_family=AF_NETLINK, nl_pid=0, 
nl_groups=00000000}, [12]) = 1100

Message the user:
write(2, "Error sending add rule data requ"..., 63Error sending add rule data 
request (No such file or directory)) = 63

The kernel is returning ENOENT. It doesn't matter which form of watch. But 
what I tested yesterday is different:

auditctl -a always,exit -F path=/tmp/nonexitent -F perm=wa -k nonexistent

into the kernel:
sendto(4, [{nlmsg_len=1084, nlmsg_type=AUDIT_ADD_RULE, 
nlmsg_flags=NLM_F_REQUEST|NLM_F_ACK, nlmsg_seq=2, nlmsg_pid=0}, 
"\x04\x00\x00\x00\x02\x00\x00\x00\x03\x00\x00\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"...], 
1084, 0, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 12) = 1084

Answer back no error
recvfrom(4, [{nlmsg_len=36, nlmsg_type=NLMSG_ERROR, nlmsg_flags=NLM_F_CAPPED, 
nlmsg_seq=2, nlmsg_pid=271266}, {error=0, msg={nlmsg_len=1084, 
nlmsg_type=AUDIT_ADD_RULE, nlmsg_flags=NLM_F_REQUEST|NLM_F_ACK, nlmsg_seq=2, 
nlmsg_pid=0}}], 8988, MSG_PEEK|MSG_DONTWAIT, {sa_family=AF_NETLINK, nl_pid=0, 
nl_groups=00000000}, [12]) = 36

It does take paths that do not exist. So, there is a difference in behavior 
based on whether it is a path or directory. That might be worth the kernel 
folks looking deeper into.
#+end_quote


-Seth