Messages in this thread | | | From | Steve Grubb <> | Subject | Re: [PATCH V2 1/2] audit: stop an old auditd being starved out by a new auditd | Date | Wed, 16 Dec 2015 11:23:19 -0500 |
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Hello Richard,
Public reply this time. :-)
On Wednesday, December 16, 2015 10:42:32 AM Richard Guy Briggs wrote: > Nothing prevents a new auditd starting up and replacing a valid > audit_pid when an old auditd is still running, effectively starving out > the old auditd since audit_pid no longer points to the old valid auditd.
I guess the first question is why do we allow something to start up a new auditd without killing off the old one? Would that be a simpler fix?
> If no message to auditd has been attempted since auditd died unnaturally > or got killed, audit_pid will still indicate it is alive. There isn't > an easy way to detect if an old auditd is still running on the existing > audit_pid other than attempting to send a message to see if it fails. > An -ECONNREFUSED almost certainly means it disappeared and can be > replaced. Other errors are not so straightforward and may indicate > transient problems that will resolve themselves and the old auditd will > recover. Yet others will likely need manual intervention for which a > new auditd will not solve the problem. > > Send a new message type (AUDIT_REPLACE) to the old auditd containing a > u32 with the PID of the new auditd. If the audit replace message > succeeds (or doesn't fail with certainty), fail to register the new > auditd and return an error (-EEXIST). > > This is expected to make the patch preventing an old auditd orphaning a > new auditd redundant. > > V2: Rename audit_ping to audit_replace, set seq and portid to 0 in > the call to audit_make_reply(). > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com> > --- > include/uapi/linux/audit.h | 1 + > kernel/audit.c | 16 +++++++++++++++- > 2 files changed, 16 insertions(+), 1 deletions(-) > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h > index 843540c..cf84991 100644 > --- a/include/uapi/linux/audit.h > +++ b/include/uapi/linux/audit.h > @@ -70,6 +70,7 @@ > #define AUDIT_TTY_SET 1017 /* Set TTY auditing status */ > #define AUDIT_SET_FEATURE 1018 /* Turn an audit feature on or off */ > #define AUDIT_GET_FEATURE 1019 /* Get which features are enabled */ > +#define AUDIT_REPLACE 1020 /* Replace auditd if this packet unanswerd */
In every case, events in the 1000 block are to configure the kernel or to ask the kernel a question. This is user space initiating. Kernel initiating events are in the 1300 block of numbers.
-Steve
> #define AUDIT_FIRST_USER_MSG 1100 /* Userspace messages mostly > uninteresting to kernel */ #define AUDIT_USER_AVC 1107 /* We filter this > differently */ > diff --git a/kernel/audit.c b/kernel/audit.c > index 36989a1..0368be2 100644 > --- a/kernel/audit.c > +++ b/kernel/audit.c > @@ -809,6 +809,16 @@ static int audit_set_feature(struct sk_buff *skb) > return 0; > } > > +static int audit_replace(pid_t pid) > +{ > + struct sk_buff *skb = audit_make_reply(0, 0, AUDIT_REPLACE, 0, 0, > + &pid, sizeof(pid)); > + > + if (!skb) > + return -ENOMEM; > + return netlink_unicast(audit_sock, skb, audit_nlk_portid, 0); > +} > + > static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh) > { > u32 seq; > @@ -870,9 +880,13 @@ static int audit_receive_msg(struct sk_buff *skb, > struct nlmsghdr *nlh) } > if (s.mask & AUDIT_STATUS_PID) { > int new_pid = s.pid; > + pid_t requesting_pid = task_tgid_vnr(current); > > - if ((!new_pid) && (task_tgid_vnr(current) != audit_pid)) > + if ((!new_pid) && (requesting_pid != audit_pid)) > return -EACCES; > + if (audit_pid && new_pid && > + audit_replace(requesting_pid) != -ECONNREFUSED) > + return -EEXIST; > if (audit_enabled != AUDIT_OFF) > audit_log_config_change("audit_pid", new_pid, audit_pid, 1); > audit_pid = new_pid;
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