[PATCH v4 01/11] net/scm: Regularize compat handling of scm_detach_fds()

Kees Cook
2020-06-16T03:26:35Z

Duplicate the cleanups from commit 2618d530dd8b ("net/scm: cleanup
scm_detach_fds") into the compat code.

Move the check added in commit 1f466e1f15cf ("net: cleanly handle kernel
vs user buffers for ->msg_control") to before the compat call, even
though it should be impossible for an in-kernel call to also be compat.

Correct the int "flags" argument to unsigned int to match fd_install()
and similar APIs.

Regularize any remaining differences, including a whitespace issue,
a checkpatch warning, and add the check from commit 6900317f5eff ("net,
scm: fix PaX detected msg_controllen overflow in scm_detach_fds") which
fixed an overflow unique to 64-bit. To avoid confusion when comparing
the compat handler to the native handler, just include the same check
in the compat handler.

Fixes: 48a87cc26c13 ("net: netprio: fd passed in SCM_RIGHTS datagram not set correctly")
Fixes: d84295067fc7 ("net: net_cls: fd passed in SCM_RIGHTS datagram not set correctly")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/net/scm.h | 1 +
net/compat.c | 55 +++++++++++++++++++++--------------------------
net/core/scm.c | 18 ++++++++--------
3 files changed, 35 insertions(+), 39 deletions(-)

diff --git a/include/net/scm.h b/include/net/scm.h
index 1ce365f4c256..581a94d6c613 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -37,6 +37,7 @@ struct scm_cookie {
#endif
};

+int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags);
void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm);
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);
diff --git a/net/compat.c b/net/compat.c
index 5e3041a2c37d..27d477fdcaa0 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -281,39 +281,31 @@ int put_cmsg_compat(struct msghdr *kmsg, int level, int type, int len, void *dat
return 0;
}

-void scm_detach_fds_compat(struct msghdr *kmsg, struct scm_cookie *scm)
+static int scm_max_fds_compat(struct msghdr *msg)
{
- struct compat_cmsghdr __user *cm = (struct compat_cmsghdr __user *) kmsg->msg_control;
- int fdmax = (kmsg->msg_controllen - sizeof(struct compat_cmsghdr)) / sizeof(int);
- int fdnum = scm->fp->count;
- struct file **fp = scm->fp->fp;
- int __user *cmfptr;
- int err = 0, i;
+ if (msg->msg_controllen <= sizeof(struct compat_cmsghdr))
+ return 0;
+ return (msg->msg_controllen - sizeof(struct compat_cmsghdr)) / sizeof(int);
+}

- if (fdnum < fdmax)
- fdmax = fdnum;
+void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm)
+{
+ struct compat_cmsghdr __user *cm =
+ (struct compat_cmsghdr __user *)msg->msg_control;
+ unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
+ int fdmax = min_t(int, scm_max_fds_compat(msg), scm->fp->count);
+ int __user *cmsg_data = CMSG_USER_DATA(cm);
+ int err = 0, i;

- for (i = 0, cmfptr = (int __user *) CMSG_COMPAT_DATA(cm); i < fdmax; i++, cmfptr++) {
- int new_fd;
- err = security_file_receive(fp[i]);
+ for (i = 0; i < fdmax; i++) {
+ err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
if (err)
break;
- err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & kmsg->msg_flags
- ? O_CLOEXEC : 0);
- if (err < 0)
- break;
- new_fd = err;
- err = put_user(new_fd, cmfptr);
- if (err) {
- put_unused_fd(new_fd);
- break;
- }
- /* Bump the usage count and install the file. */
- fd_install(new_fd, get_file(fp[i]));
}

if (i > 0) {
int cmlen = CMSG_COMPAT_LEN(i * sizeof(int));
+
err = put_user(SOL_SOCKET, &cm->cmsg_level);
if (!err)
err = put_user(SCM_RIGHTS, &cm->cmsg_type);
@@ -321,16 +313,19 @@ void scm_detach_fds_compat(struct msghdr *kmsg, struct scm_cookie *scm)
err = put_user(cmlen, &cm->cmsg_len);
if (!err) {
cmlen = CMSG_COMPAT_SPACE(i * sizeof(int));
- kmsg->msg_control += cmlen;
- kmsg->msg_controllen -= cmlen;
+ if (msg->msg_controllen < cmlen)
+ cmlen = msg->msg_controllen;
+ msg->msg_control += cmlen;
+ msg->msg_controllen -= cmlen;
}
}
- if (i < fdnum)
- kmsg->msg_flags |= MSG_CTRUNC;
+
+ if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
+ msg->msg_flags |= MSG_CTRUNC;

/*
- * All of the files that fit in the message have had their
- * usage counts incremented, so we just free the list.
+ * All of the files that fit in the message have had their usage counts
+ * incremented, so we just free the list.
*/
__scm_destroy(scm);
}
diff --git a/net/core/scm.c b/net/core/scm.c
index 875df1c2989d..6151678c73ed 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -280,7 +280,7 @@ void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_inter
}
EXPORT_SYMBOL(put_cmsg_scm_timestamping);

-static int __scm_install_fd(struct file *file, int __user *ufd, int o_flags)
+int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags)
{
struct socket *sock;
int new_fd;
@@ -319,29 +319,29 @@ static int scm_max_fds(struct msghdr *msg)

void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
{
- struct cmsghdr __user *cm
- = (__force struct cmsghdr __user*)msg->msg_control;
- int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
+ struct cmsghdr __user *cm =
+ (__force struct cmsghdr __user *)msg->msg_control;
+ unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
int __user *cmsg_data = CMSG_USER_DATA(cm);
int err = 0, i;

+ /* no use for FD passing from kernel space callers */
+ if (WARN_ON_ONCE(!msg->msg_control_is_user))
+ return;
+
if (msg->msg_flags & MSG_CMSG_COMPAT) {
scm_detach_fds_compat(msg, scm);
return;
}

- /* no use for FD passing from kernel space callers */
- if (WARN_ON_ONCE(!msg->msg_control_is_user))
- return;
-
for (i = 0; i < fdmax; i++) {
err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
if (err)
break;
}

- if (i > 0) {
+ if (i > 0) {
int cmlen = CMSG_LEN(i * sizeof(int));

err = put_user(SOL_SOCKET, &cm->cmsg_level);
--
2.25.1