Re: [PATCH v2] audit: use proper refcount locking on audit_sock
From: Paul Moore <paul@paul-moore.com>
Date: 2016-12-12 20:18:45
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lkml
On Mon, Dec 12, 2016 at 5:03 AM, Richard Guy Briggs [off-list ref] wrote:
Resetting audit_sock appears to be racy. audit_sock was being copied and dereferenced without using a refcount on the source sock. Bump the refcount on the underlying sock when we store a refrence in audit_sock and release it when we reset audit_sock. audit_sock modification needs the audit_cmd_mutex. See: https://lkml.org/lkml/2016/11/26/232 Thanks to Eric Dumazet [off-list ref] and Cong Wang [off-list ref] on ideas how to fix it. Signed-off-by: Richard Guy Briggs <redacted> --- There has been a lot of change in the audit code that is about to go upstream to address audit queue issues. This patch is based on the source tree: git://git.infradead.org/users/pcmoore/audit#next --- kernel/audit.c | 34 ++++++++++++++++++++++++++++------ 1 files changed, 28 insertions(+), 6 deletions(-)
My previous question about testing still stands, but I took a closer look and have some additional comments, see below ...
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diff --git a/kernel/audit.c b/kernel/audit.c index f20eee0..439f7f3 100644 --- a/kernel/audit.c +++ b/kernel/audit.c@@ -452,7 +452,9 @@ static void auditd_reset(void) struct sk_buff *skb; /* break the connection */ + sock_put(audit_sock); audit_pid = 0; + audit_nlk_portid = 0; audit_sock = NULL; /* flush all of the retry queue to the hold queue */@@ -478,6 +480,12 @@ static int kauditd_send_unicast_skb(struct sk_buff *skb) if (rc >= 0) { consume_skb(skb); rc = 0; + } else { + if (rc & (-ENOMEM|-EPERM|-ECONNREFUSED)) {
I dislike the way you wrote this because instead of simply looking at this to see if it correct I need to sort out all the bits and find out if there are other error codes that could run afoul of this check ... make it simple, e.g. (rc == -ENOMEM || rc == -EPERM || ...). Actually, since EPERM is 1, -EPERM (-1 in two's compliment is 0xffffffff) is going to cause this to be true for pretty much any value of rc, yes?
+ mutex_lock(&audit_cmd_mutex); + auditd_reset(); + mutex_unlock(&audit_cmd_mutex); + }
The code in audit#next handles netlink_unicast() errors in kauditd_thread() and you are adding error handling code here in kauditd_send_unicast_skb() ... that's messy. I don't care too much where the auditd_reset() call is made, but let's only do it in one function; FWIW, I originally put the error handling code in kauditd_thread() because there was other error handling code that needed to done in that scope so it resulted in cleaner code. Related, I see you are now considering ENOMEM to be a fatal condition, that differs from the AUDITD_BAD macro in kauditd_thread(); this difference needs to be reconciled. Finally, you should update the comment header block for auditd_reset() that it needs to be called with the audit_cmd_mutex held.
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@@ -1004,17 +1018,22 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh) return -EACCES; } if (audit_pid && new_pid && - audit_replace(requesting_pid) != -ECONNREFUSED) { + (audit_replace(requesting_pid) & (-ECONNREFUSED|-EPERM|-ENOMEM))) {
Do we simply want to treat any error here as fatal, and not just ECONN/EPERM/ENOMEM? If not, let's come up with a single macro to handle the fatal netlink_unicast() return codes so we have some chance to keep things consistent in the future. -- paul moore www.paul-moore.com