[PATCH net-next] scm: Don't use struct ucred in NETLINK_CB and struct scm_cookie.
From: Eric W. Biederman <hidden>
Date: 2012-09-07 04:20:12
Passing uids and gids on NETLINK_CB from a process in one user namespace to a process in another user namespace can result in the wrong uid or gid being presented to userspace. Avoid that problem by passing kuids and kgids instead. - define struct scm_creds for use in scm_cookie and netlink_skb_parms that holds uid and gid information in kuid_t and kgid_t. - Modify scm_set_cred to fill out scm_creds by heand instead of using cred_to_ucred to fill out struct ucred. This conversion ensures userspace does not get incorrect uid or gid values to look at. - Modify scm_recv to convert from struct scm_creds to struct ucred before copying credential values to userspace. - Modify __scm_send to populate struct scm_creds on in the scm_cookie, instead of just copying struct ucred from userspace. - Modify netlink_sendmsg to copy scm_creds instead of struct ucred into the NETLINK_CB. Signed-off-by: "Eric W. Biederman" <redacted> --- include/linux/netlink.h | 3 ++- include/net/scm.h | 23 +++++++++++++++++++---- net/core/scm.c | 17 +++++++++++------ net/netlink/af_netlink.c | 2 +- 4 files changed, 33 insertions(+), 12 deletions(-)
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index c9fdde2..df73cf4 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h@@ -153,6 +153,7 @@ struct nlattr { #include <linux/capability.h> #include <linux/skbuff.h> +#include <net/scm.h> struct net;
@@ -162,7 +163,7 @@ static inline struct nlmsghdr *nlmsg_hdr(const struct sk_buff *skb) } struct netlink_skb_parms { - struct ucred creds; /* Skb credentials */ + struct scm_creds creds; /* Skb credentials */ __u32 pid; __u32 dst_group; struct sock *ssk;
diff --git a/include/net/scm.h b/include/net/scm.h
index 079d788..000b6f7 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h@@ -12,6 +12,12 @@ */ #define SCM_MAX_FD 253 +struct scm_creds { + u32 pid; + kuid_t uid; + kgid_t gid; +}; + struct scm_fp_list { short count; short max;
@@ -22,7 +28,7 @@ struct scm_cookie { struct pid *pid; /* Skb credentials */ const struct cred *cred; struct scm_fp_list *fp; /* Passed files */ - struct ucred creds; /* Skb credentials */ + struct scm_creds creds; /* Skb credentials */ #ifdef CONFIG_SECURITY_NETWORK u32 secid; /* Passed security ID */ #endif
@@ -49,7 +55,9 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm, { scm->pid = get_pid(pid); scm->cred = cred ? get_cred(cred) : NULL; - cred_to_ucred(pid, cred, &scm->creds); + scm->creds.pid = pid_vnr(pid); + scm->creds.uid = cred ? cred->euid : INVALID_UID; + scm->creds.gid = cred ? cred->egid : INVALID_GID; } static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
@@ -110,8 +118,15 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg, return; } - if (test_bit(SOCK_PASSCRED, &sock->flags)) - put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(scm->creds), &scm->creds); + if (test_bit(SOCK_PASSCRED, &sock->flags)) { + struct user_namespace *current_ns = current_user_ns(); + struct ucred ucreds = { + .pid = scm->creds.pid, + .uid = from_kuid_munged(current_ns, scm->creds.uid), + .gid = from_kgid_munged(current_ns, scm->creds.gid), + }; + put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds); + } scm_destroy_cred(scm);
diff --git a/net/core/scm.c b/net/core/scm.c
index 5472ae7..64b41d8 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c@@ -155,19 +155,21 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) break; case SCM_CREDENTIALS: { + struct ucred creds; kuid_t uid; kgid_t gid; if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred))) goto error; - memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred)); - err = scm_check_creds(&p->creds); + memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred)); + err = scm_check_creds(&creds); if (err) goto error; - if (!p->pid || pid_vnr(p->pid) != p->creds.pid) { + p->creds.pid = creds.pid; + if (!p->pid || pid_vnr(p->pid) != creds.pid) { struct pid *pid; err = -ESRCH; - pid = find_get_pid(p->creds.pid); + pid = find_get_pid(creds.pid); if (!pid) goto error; put_pid(p->pid);
@@ -175,11 +177,14 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) } err = -EINVAL; - uid = make_kuid(current_user_ns(), p->creds.uid); - gid = make_kgid(current_user_ns(), p->creds.gid); + uid = make_kuid(current_user_ns(), creds.uid); + gid = make_kgid(current_user_ns(), creds.gid); if (!uid_valid(uid) || !gid_valid(gid)) goto error; + p->creds.uid = uid; + p->creds.gid = gid; + if (!p->cred || !uid_eq(p->cred->euid, uid) || !gid_eq(p->cred->egid, gid)) {
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 7cb7867..6473267 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c@@ -1398,7 +1398,7 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock, NETLINK_CB(skb).pid = nlk->pid; NETLINK_CB(skb).dst_group = dst_group; - memcpy(NETLINK_CREDS(skb), &siocb->scm->creds, sizeof(struct ucred)); + NETLINK_CB(skb).creds = siocb->scm->creds; err = -EFAULT; if (memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len)) {
--
1.7.5.4