Re: [PATCH v4 2/3] Send comm and cmdline in SCM_PROCINFO

From: Richard Guy Briggs
Date: Tue Jan 14 2014 - 23:03:23 EST

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In reply to: Jan Kaluza: "[PATCH v4 2/3] Send comm and cmdline in SCM_PROCINFO"
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On 14/01/13, Jan Kaluza wrote:
> Server-like processes in many cases need credentials and other
> metadata of the peer, to decide if the calling process is allowed to
> request a specific action, or the server just wants to log away this
> type of information for auditing tasks.
>
> The current practice to retrieve such process metadata is to look that
> information up in procfs with the $PID received over SCM_CREDENTIALS.
> This is sufficient for long-running tasks, but introduces a race which
> cannot be worked around for short-living processes; the calling
> process and all the information in /proc/$PID/ is gone before the
> receiver of the socket message can look it up.
>
> This introduces a new SCM type called SCM_PROCINFO to allow the direct
> attaching of "comm" and "cmdline" to SCM, which is significantly more
> efficient and will reliably avoid the race with the round-trip over
> procfs.
>
> To achieve that, new struct called unix_skb_parms_scm had to be created,
> because otherwise unix_skb_parms would be too big.
>
> scm_get_current_procinfo is inspired by ./fs/proc/base.c.
>
> Signed-off-by: Jan Kaluza <jkaluza@xxxxxxxxxx>

Acked-by: Richard Guy Briggs <rgb@xxxxxxxxxx>

> ---
> include/linux/socket.h | 2 ++
> include/net/af_unix.h | 11 +++++++--
> include/net/scm.h | 24 +++++++++++++++++++
> net/core/scm.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++
> net/unix/af_unix.c | 57 +++++++++++++++++++++++++++++++++++++------
> 5 files changed, 150 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index eeac565..5a41f35 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -131,6 +131,8 @@ static inline struct cmsghdr * cmsg_nxthdr (struct msghdr *__msg, struct cmsghdr
> #define SCM_CREDENTIALS 0x02 /* rw: struct ucred */
> #define SCM_SECURITY 0x03 /* rw: security label */
> #define SCM_AUDIT 0x04 /* rw: struct uaudit */
> +#define SCM_PROCINFO 0x05 /* rw: comm + cmdline (NULL terminated
> + array of char *) */
>
> struct ucred {
> __u32 pid;
> diff --git a/include/net/af_unix.h b/include/net/af_unix.h
> index 3b9d22a..05c7678 100644
> --- a/include/net/af_unix.h
> +++ b/include/net/af_unix.h
> @@ -27,6 +27,13 @@ struct unix_address {
> struct sockaddr_un name[0];
> };
>
> +struct unix_skb_parms_scm {
> + kuid_t loginuid;
> + unsigned int sessionid;
> + char *procinfo;
> + int procinfo_len;
> +};
> +
> struct unix_skb_parms {
> struct pid *pid; /* Skb credentials */
> kuid_t uid;
> @@ -36,12 +43,12 @@ struct unix_skb_parms {
> u32 secid; /* Security ID */
> #endif
> u32 consumed;
> - kuid_t loginuid;
> - unsigned int sessionid;
> + struct unix_skb_parms_scm *scm;
> };
>
> #define UNIXCB(skb) (*(struct unix_skb_parms *)&((skb)->cb))
> #define UNIXSID(skb) (&UNIXCB((skb)).secid)
> +#define UNIXSCM(skb) (*(UNIXCB((skb)).scm))
>
> #define unix_state_lock(s) spin_lock(&unix_sk(s)->lock)
> #define unix_state_unlock(s) spin_unlock(&unix_sk(s)->lock)
> diff --git a/include/net/scm.h b/include/net/scm.h
> index 67de64f..f084e19 100644
> --- a/include/net/scm.h
> +++ b/include/net/scm.h
> @@ -30,11 +30,17 @@ struct scm_fp_list {
> struct file *fp[SCM_MAX_FD];
> };
>
> +struct scm_procinfo {
> + char *procinfo;
> + int len;
> +};
> +
> struct scm_cookie {
> struct pid *pid; /* Skb credentials */
> struct scm_fp_list *fp; /* Passed files */
> struct scm_creds creds; /* Skb credentials */
> struct scm_audit audit; /* Skb audit */
> + struct scm_procinfo procinfo; /* Skb procinfo */
> #ifdef CONFIG_SECURITY_NETWORK
> u32 secid; /* Passed security ID */
> #endif
> @@ -45,6 +51,7 @@ void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm);
> int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm);
> void __scm_destroy(struct scm_cookie *scm);
> struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl);
> +int scm_get_current_procinfo(char **procinfo);
>
> #ifdef CONFIG_SECURITY_NETWORK
> static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
> @@ -72,10 +79,20 @@ static inline void scm_set_audit(struct scm_cookie *scm,
> scm->audit.sessionid = sessionid;
> }
>
> +static inline void scm_set_procinfo(struct scm_cookie *scm,
> + char *procinfo, int len)
> +{
> + scm->procinfo.procinfo = procinfo;
> + scm->procinfo.len = len;
> +}
> +
> static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
> {
> put_pid(scm->pid);
> scm->pid = NULL;
> + kfree(scm->procinfo.procinfo);
> + scm->procinfo.procinfo = NULL;
> + scm->procinfo.len = 0;
> }
>
> static __inline__ void scm_destroy(struct scm_cookie *scm)
> @@ -88,6 +105,8 @@ static __inline__ void scm_destroy(struct scm_cookie *scm)
> static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
> struct scm_cookie *scm, bool forcecreds)
> {
> + char *procinfo;
> + int len;
> memset(scm, 0, sizeof(*scm));
> scm->creds.uid = INVALID_UID;
> scm->creds.gid = INVALID_GID;
> @@ -96,6 +115,9 @@ static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
> current_gid());
> scm_set_audit(scm, audit_get_loginuid(current),
> audit_get_sessionid(current));
> + len = scm_get_current_procinfo(&procinfo);
> + if (len > 0)
> + scm_set_procinfo(scm, procinfo, len);
> }
> unix_get_peersec_dgram(sock, scm);
> if (msg->msg_controllen <= 0)
> @@ -148,6 +170,8 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
> };
> put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
> put_cmsg(msg, SOL_SOCKET, SCM_AUDIT, sizeof(uaudits), &uaudits);
> + put_cmsg(msg, SOL_SOCKET, SCM_PROCINFO, scm->procinfo.len,
> + scm->procinfo.procinfo);
> }
>
> scm_destroy_cred(scm);
> diff --git a/net/core/scm.c b/net/core/scm.c
> index b442e7e..4accb07 100644
> --- a/net/core/scm.c
> +++ b/net/core/scm.c
> @@ -339,3 +339,68 @@ struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
> return new_fpl;
> }
> EXPORT_SYMBOL(scm_fp_dup);
> +
> +int scm_get_current_procinfo(char **procinfo)
> +{
> + int res = 0;
> + unsigned int len;
> + char *buffer = NULL;
> + struct mm_struct *mm;
> + int comm_len = strlen(current->comm);
> +
> + *procinfo = NULL;
> +
> + buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
> + if (!buffer)
> + return -ENOMEM;
> +
> + mm = get_task_mm(current);
> + if (!mm)
> + goto out;
> + if (!mm->arg_end)
> + goto out_mm; /* Shh! No looking before we're done */
> +
> + len = mm->arg_end - mm->arg_start;
> +
> + if (len > PAGE_SIZE)
> + len = PAGE_SIZE;
> +
> + res = access_process_vm(current, mm->arg_start, buffer, len, 0);
> +
> + /* If the nul at the end of args has been overwritten, then
> + * assume application is using setproctitle(3).
> + */
> + if (res > 0 && buffer[res-1] != '\0' && len < PAGE_SIZE) {
> + len = strnlen(buffer, res);
> + if (len < res) {
> + res = len;
> + } else {
> + len = mm->env_end - mm->env_start;
> + if (len > PAGE_SIZE - res)
> + len = PAGE_SIZE - res;
> + res += access_process_vm(current, mm->env_start,
> + buffer+res, len, 0);
> + res = strnlen(buffer, res);
> + }
> + }
> +
> + /* strlen(comm) + \0 + len of cmdline */
> + len = comm_len + 1 + res;
> + *procinfo = kmalloc(len, GFP_KERNEL);
> + if (!*procinfo) {
> + res = -ENOMEM;
> + goto out_mm;
> + }
> +
> + memcpy(*procinfo, current->comm, comm_len + 1); /* include \0 */
> + if (res > 0)
> + memcpy(*procinfo + comm_len + 1, buffer, res);
> + res = len;
> +
> +out_mm:
> + mmput(mm);
> +out:
> + kfree(buffer);
> + return res;
> +}
> +EXPORT_SYMBOL(scm_get_current_procinfo);
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index bc02a25..35ab97f0 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1361,9 +1361,14 @@ static void unix_destruct_scm(struct sk_buff *skb)
> struct scm_cookie scm;
> memset(&scm, 0, sizeof(scm));
> scm.pid = UNIXCB(skb).pid;
> + if (UNIXCB(skb).scm) {
> + scm.procinfo.procinfo = UNIXSCM(skb).procinfo;
> + scm.procinfo.len = UNIXSCM(skb).procinfo_len;
> + }
> if (UNIXCB(skb).fp)
> unix_detach_fds(&scm, skb);
>
> + kfree(UNIXCB(skb).scm);
> /* Alas, it calls VFS */
> /* So fscking what? fput() had been SMP-safe since the last Summer */
> scm_destroy(&scm);
> @@ -1410,15 +1415,31 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
> {
> int err = 0;
>
> + if (!UNIXCB(skb).scm) {
> + UNIXCB(skb).scm = kmalloc(sizeof(struct unix_skb_parms_scm),
> + GFP_KERNEL);
> + if (!UNIXCB(skb).scm)
> + return -ENOMEM;
> + }
> +
> UNIXCB(skb).pid = get_pid(scm->pid);
> UNIXCB(skb).uid = scm->creds.uid;
> UNIXCB(skb).gid = scm->creds.gid;
> - UNIXCB(skb).loginuid = scm->audit.loginuid;
> - UNIXCB(skb).sessionid = scm->audit.sessionid;
> + UNIXSCM(skb).loginuid = scm->audit.loginuid;
> + UNIXSCM(skb).sessionid = scm->audit.sessionid;
> UNIXCB(skb).fp = NULL;
> if (scm->fp && send_fds)
> err = unix_attach_fds(scm, skb);
>
> + UNIXSCM(skb).procinfo = NULL;
> + if (scm->procinfo.procinfo) {
> + UNIXSCM(skb).procinfo_len = scm->procinfo.len;
> + UNIXSCM(skb).procinfo = kmemdup(scm->procinfo.procinfo,
> + scm->procinfo.len, GFP_KERNEL);
> + if (!UNIXSCM(skb).procinfo)
> + return -ENOMEM;
> + }
> +
> skb->destructor = unix_destruct_scm;
> return err;
> }
> @@ -1438,8 +1459,10 @@ static void maybe_add_creds(struct sk_buff *skb, const struct socket *sock,
> test_bit(SOCK_PASSCRED, &other->sk_socket->flags)) {
> UNIXCB(skb).pid = get_pid(task_tgid(current));
> current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid);
> - UNIXCB(skb).loginuid = audit_get_loginuid(current);
> - UNIXCB(skb).sessionid = audit_get_sessionid(current);
> + UNIXSCM(skb).loginuid = audit_get_loginuid(current);
> + UNIXSCM(skb).sessionid = audit_get_sessionid(current);
> + UNIXSCM(skb).procinfo_len = scm_get_current_procinfo(
> + &UNIXSCM(skb).procinfo);
> }
> }
>
> @@ -1833,7 +1856,17 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
> memset(&tmp_scm, 0, sizeof(tmp_scm));
> }
> scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
> - scm_set_audit(siocb->scm, UNIXCB(skb).loginuid, UNIXCB(skb).sessionid);
> + if (UNIXCB(skb).scm) {
> + scm_set_audit(siocb->scm, UNIXSCM(skb).loginuid,
> + UNIXSCM(skb).sessionid);
> + if (UNIXSCM(skb).procinfo) {
> + scm_set_procinfo(siocb->scm,
> + kmemdup(UNIXSCM(skb).procinfo,
> + UNIXSCM(skb).procinfo_len,
> + GFP_KERNEL),
> + UNIXSCM(skb).procinfo_len);
> + }
> + }
> unix_set_secdata(siocb->scm, skb);
>
> if (!(flags & MSG_PEEK)) {
> @@ -2013,8 +2046,18 @@ again:
> } else if (test_bit(SOCK_PASSCRED, &sock->flags)) {
> /* Copy credentials */
> scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
> - scm_set_audit(siocb->scm, UNIXCB(skb).loginuid,
> - UNIXCB(skb).sessionid);
> + if (UNIXCB(skb).scm) {
> + scm_set_audit(siocb->scm,
> + UNIXSCM(skb).loginuid,
> + UNIXSCM(skb).sessionid);
> + if (UNIXSCM(skb).procinfo) {
> + scm_set_procinfo(siocb->scm,
> + kmemdup(UNIXSCM(skb).procinfo,
> + UNIXSCM(skb).procinfo_len,
> + GFP_KERNEL),
> + UNIXSCM(skb).procinfo_len);
> + }
> + }
> check_creds = 1;
> }
>
> --
> 1.8.3.1
>

- RGB

--
Richard Guy Briggs <rbriggs@xxxxxxxxxx>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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Next message: Greg Kroah-Hartman: "Re: [STABLE] find missing bug fixes in a stable kernel"
Previous message: Stephen Rothwell: "linux-next: manual merge of the md tree with the tree"
In reply to: Jan Kaluza: "[PATCH v4 2/3] Send comm and cmdline in SCM_PROCINFO"
Next in thread: Tejun Heo: "Re: [PATCH v4 0/3] Send audit/procinfo/cgroup data in socket-levelcontrol message"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]