[PATCH v2] scm: fix possible control message header alignment issue

[yuan linyu]

From: yuan linyu <linyu.y...@alcatel-sbell.com.cn>

1. put_cmsg{_compat}() may copy data to user when buffer free space less than
   control message header alignment size.
2. scm_detach_fds{_compat}() may calc wrong fdmax if control message header
   have greater alignment size.

Signed-off-by: yuan linyu <linyu.y...@alcatel-sbell.com.cn>
---
 net/compat.c   | 10 ++++++++--
 net/core/scm.c |  8 +++++---
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/net/compat.c b/net/compat.c
index 96c544b..ffe7a04 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -245,7 +245,9 @@ int put_cmsg_compat(struct msghdr *kmsg, int level, int 
type, int len, void *dat
 
        if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
                return -EFAULT;
-       if (copy_to_user(CMSG_COMPAT_DATA(cm), data, cmlen - sizeof(struct 
compat_cmsghdr)))
+       if (cmlen > CMSG_COMPAT_ALIGN(sizeof(struct compat_cmsghdr)) &&
+           copy_to_user(CMSG_COMPAT_DATA(cm), data,
+                           cmlen - CMSG_COMPAT_ALIGN(sizeof(struct 
compat_cmsghdr))))
                return -EFAULT;
        cmlen = CMSG_COMPAT_SPACE(len);
        if (kmsg->msg_controllen < cmlen)
@@ -258,12 +260,16 @@ int put_cmsg_compat(struct msghdr *kmsg, int level, int 
type, int len, void *dat
 void scm_detach_fds_compat(struct msghdr *kmsg, struct scm_cookie *scm)
 {
        struct compat_cmsghdr __user *cm = (struct compat_cmsghdr __user *) 
kmsg->msg_control;
-       int fdmax = (kmsg->msg_controllen - sizeof(struct compat_cmsghdr)) / 
sizeof(int);
+       int fdmax = 0;
        int fdnum = scm->fp->count;
        struct file **fp = scm->fp->fp;
        int __user *cmfptr;
        int err = 0, i;
 
+       if (kmsg->msg_controllen > CMSG_COMPAT_ALIGN(sizeof(struct 
compat_cmsghdr)))
+               fdmax = (kmsg->msg_controllen -
+                        CMSG_COMPAT_ALIGN(sizeof(struct compat_cmsghdr))) / 
sizeof(int);
+
        if (fdnum < fdmax)
                fdmax = fdnum;
 
diff --git a/net/core/scm.c b/net/core/scm.c
index d882043..b2e60fd 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -238,7 +238,9 @@ int put_cmsg(struct msghdr * msg, int level, int type, int 
len, void *data)
        err = -EFAULT;
        if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
                goto out;
-       if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
+       if (cmlen > CMSG_ALIGN(sizeof(struct cmsghdr)) &&
+           copy_to_user(CMSG_DATA(cm), data,
+                           cmlen - CMSG_ALIGN(sizeof(struct cmsghdr))))
                goto out;
        cmlen = CMSG_SPACE(len);
        if (msg->msg_controllen < cmlen)
@@ -267,8 +269,8 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie 
*scm)
                return;
        }
 
-       if (msg->msg_controllen > sizeof(struct cmsghdr))
-               fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
+       if (msg->msg_controllen > CMSG_ALIGN(sizeof(struct cmsghdr)))
+               fdmax = ((msg->msg_controllen - CMSG_ALIGN(sizeof(struct 
cmsghdr)))
                         / sizeof(int));
 
        if (fdnum < fdmax)
-- 
2.7.4