[PATCH 1/3] net: add a CMSG_USER_DATA macro

Christoph Hellwig
2020-05-11T11:59:23Z

Add a variant of CMSG_DATA that operates on user pointer to avoid
sparse warnings about casting to/from user pointers. Also fix up
CMSG_DATA to rely on the gcc extension that allows void pointer
arithmetics to cut down on the amount of casts.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
include/linux/socket.h | 5 ++++-
net/core/scm.c | 4 ++--
2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 54338fac45cb7..4cc64d611cf49 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -94,7 +94,10 @@ struct cmsghdr {

#define CMSG_ALIGN(len) ( ((len)+sizeof(long)-1) & ~(sizeof(long)-1) )

-#define CMSG_DATA(cmsg) ((void *)((char *)(cmsg) + sizeof(struct cmsghdr)))
+#define CMSG_DATA(cmsg) \
+ ((void *)(cmsg) + sizeof(struct cmsghdr))
+#define CMSG_USER_DATA(cmsg) \
+ ((void __user *)(cmsg) + sizeof(struct cmsghdr))
#define CMSG_SPACE(len) (sizeof(struct cmsghdr) + CMSG_ALIGN(len))
#define CMSG_LEN(len) (sizeof(struct cmsghdr) + (len))

diff --git a/net/core/scm.c b/net/core/scm.c
index dc6fed1f221c4..abfdc85a64c1b 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -236,7 +236,7 @@ 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 (copy_to_user(CMSG_USER_DATA(cm), data, cmlen - sizeof(*cm)))
goto out;
cmlen = CMSG_SPACE(len);
if (msg->msg_controllen < cmlen)
@@ -300,7 +300,7 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
if (fdnum < fdmax)
fdmax = fdnum;

- for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
+ for (i=0, cmfptr =(int __user *)CMSG_USER_DATA(cm); i<fdmax;
i++, cmfptr++)
{
struct socket *sock;
--
2.26.2