Re: [PATCH] Race-free auditd shutdown credentials

The attached patch addresses the problem with getting the shutdown information in a race-free way. It creates a new message type AUDIT_TERM_INFO, which is used by the audit daemon to query who issued the shutdown. It requires the placement of a hook function that gathers the information.

diff -urB linux-2.6.9.orig/include/linux/audit.h linux-2.6.9/include/linux/audit.h --- linux-2.6.9.orig/include/linux/audit.h 2005-04-26 15:41:58.000000000 -0400 +++ linux-2.6.9/include/linux/audit.h 2005-04-26 16:09:46.000000000 -0400 @@ -38,6 +38,7 @@ #define AUDIT_WATCH_INS 1007 /* Insert file/dir watch entry */ #define AUDIT_WATCH_REM 1008 /* Remove file/dir watch entry */ #define AUDIT_WATCH_LIST 1009 /* List all watches */ +#define AUDIT_TERM_INFO 1010 /* Get termination information */ #define AUDIT_KERNEL 2000 /* Asynchronous audit record. NOT A REQUEST. */ /* Rule flags */ @@ -201,6 +202,11 @@ }; +struct audit_term_info { + uid_t uid; + pid_t pid; +}; + struct audit_buffer; struct audit_context; struct inode; @@ -297,6 +303,7 @@ int done, int multi, void *payload, int size); extern void audit_log_lost(const char *message); +extern void audit_kill_info(int sig, struct task_struct *t); #else #define audit_log(t,f,...) do { ; } while (0) #define audit_log_start(t) ({ NULL; }) @@ -312,6 +319,7 @@ #define audit_set_backlog_limit(l) do { ; } while (0) #define audit_set_enabled(s) do { ; } while (0) #define audit_set_failure(s) do { ; } while (0) +#define audit_kill_info(s,t) do { ; } while (0) #endif #endif #endif diff -urB linux-2.6.9.orig/kernel/audit.c linux-2.6.9/kernel/audit.c --- linux-2.6.9.orig/kernel/audit.c 2005-04-26 15:42:00.000000000 -0400 +++ linux-2.6.9/kernel/audit.c 2005-04-26 16:09:46.000000000 -0400 @@ -68,7 +68,7 @@ /* If audit records are to be written to the netlink socket, audit_pid * contains the (non-zero) pid. */ -static int audit_pid; +int audit_pid; /* If audit_limit is non-zero, limit the rate of sending audit records * to that number per second. This prevents DoS attacks, but results in @@ -79,6 +79,10 @@ static int audit_backlog_limit = 64; static atomic_t audit_backlog = ATOMIC_INIT(0); +/* The identity of the user shutting down the audit system. */ +uid_t audit_kill_uid; +pid_t audit_kill_pid;

+ /* Records can be lost in several ways: 0) [suppressed in audit_alloc] 1) out of memory in audit_log_start [kmalloc of struct audit_buffer] @@ -320,6 +324,7 @@ case AUDIT_DEL: case AUDIT_WATCH_INS: case AUDIT_WATCH_REM: + case AUDIT_TERM_INFO: if (!cap_raised(eff_cap, CAP_AUDIT_CONTROL)) err = -EPERM; break; @@ -343,6 +348,7 @@ struct audit_buffer *ab; u16 msg_type = nlh->nlmsg_type; uid_t loginuid; /* loginuid of sender */ + struct audit_term_info term_data; err = audit_netlink_ok(NETLINK_CB(skb).eff_cap, msg_type); if (err) @@ -429,6 +435,12 @@ NETLINK_CB(skb).pid, uid, seq, data); break; + case AUDIT_TERM_INFO: + term_data.uid = audit_kill_uid; + term_data.pid = audit_kill_pid; + audit_send_reply(NETLINK_CB(skb).pid, seq, AUDIT_TERM_INFO, + 0, 0, &term_data, sizeof(term_data)); + break; default: err = -EINVAL; break; @@ -572,6 +584,8 @@ audit_panic("cannot initialize netlink socket"); audit_initialized = 1; + audit_kill_uid = -1; + audit_kill_pid = -1; audit_enabled = audit_default; audit_filesystem_init(); audit_log(NULL, "initialized"); diff -urB linux-2.6.9.orig/kernel/auditsc.c linux-2.6.9/kernel/auditsc.c --- linux-2.6.9.orig/kernel/auditsc.c 2005-04-26 15:42:00.000000000 -0400 +++ linux-2.6.9/kernel/auditsc.c 2005-04-26 16:09:46.000000000 -0400 @@ -1134,3 +1134,22 @@ audit_notify_watch_exit: return ret; } + +void audit_kill_info(int sig, struct task_struct *t) +{ + extern pid_t audit_kill_pid; + extern uid_t audit_kill_uid; + extern int audit_pid; + + if (unlikely(audit_pid && t->pid == audit_pid)) { + if (sig == SIGTERM || sig == SIGKILL) { + struct audit_context *ctx = current->audit_context; + audit_kill_pid = current->pid; + if (ctx) + audit_kill_uid = ctx->loginuid; + else + audit_kill_uid = current->uid; + }

+ } +} + diff -urB linux-2.6.9.orig/kernel/signal.c linux-2.6.9/kernel/signal.c --- linux-2.6.9.orig/kernel/signal.c 2005-04-26 15:42:00.000000000 -0400 +++ linux-2.6.9/kernel/signal.c 2005-04-26 16:43:19.000000000 -0400 @@ -21,6 +21,7 @@ #include <linux/binfmts.h> #include <linux/security.h> #include <linux/ptrace.h> +#include <linux/audit.h> #include <asm/param.h> #include <asm/uaccess.h> #include <asm/unistd.h> @@ -623,6 +624,10 @@ int error = -EINVAL; if (sig < 0 || sig > _NSIG) return error; + + /* Let audit system examine the signal */ + audit_kill_info(sig, t);

+ error = -EPERM; if ((!info || ((unsigned long)info != 1 && (unsigned long)info != 2 && SI_FROMUSER(info))) diff -urB linux-2.6.9.orig/security/selinux/nlmsgtab.c linux-2.6.9/security/selinux/nlmsgtab.c --- linux-2.6.9.orig/security/selinux/nlmsgtab.c 2005-04-26 15:42:02.000000000 -0400 +++ linux-2.6.9/security/selinux/nlmsgtab.c 2005-04-26 16:09:46.000000000 -0400 @@ -97,6 +97,7 @@ { AUDIT_WATCH_INS, NETLINK_AUDIT_SOCKET__NLMSG_WRITE }, { AUDIT_WATCH_REM, NETLINK_AUDIT_SOCKET__NLMSG_WRITE }, { AUDIT_WATCH_LIST, NETLINK_AUDIT_SOCKET__NLMSG_READPRIV }, + { AUDIT_TERM_INFO, NETLINK_AUDIT_SOCKET__NLMSG_READ }, };