[PATCH v5 2/7] fs: Move __scm_install_fd() to __fd_install_received()

Kees Cook
2020-06-17T22:03:45Z

In preparation for users of the "install a received file" logic outside
of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
net/core/scm.c to __fd_install_received() in fs/file.c, and provide a
wrapper named fd_install_received_user(), as future patches will change
the interface to __fd_install_received().

Signed-off-by: Kees Cook <keescook@chromium.org>
---
fs/file.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/file.h | 8 ++++++++
include/net/scm.h | 1 -
net/compat.c | 2 +-
net/core/scm.c | 32 +------------------------------
5 files changed, 55 insertions(+), 33 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index abb8b7081d7a..f2167d6feec6 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -11,6 +11,7 @@
#include <linux/export.h>
#include <linux/fs.h>
#include <linux/mm.h>
+#include <linux/net.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/file.h>
@@ -18,6 +19,8 @@
#include <linux/bitops.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
+#include <net/cls_cgroup.h>
+#include <net/netprio_cgroup.h>

unsigned int sysctl_nr_open __read_mostly = 1024*1024;
unsigned int sysctl_nr_open_min = BITS_PER_LONG;
@@ -931,6 +934,48 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
return err;
}

+/**
+ * __fd_install_received() - Install received file into file descriptor table
+ *
+ * @file: struct file that was received from another process
+ * @ufd: __user pointer to write new fd number to
+ * @o_flags: the O_* flags to apply to the new fd entry
+ *
+ * Installs a received file into the file descriptor table, with appropriate
+ * checks and count updates. Writes the fd number to userspace.
+ *
+ * Returns -ve on error.
+ */
+int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_flags)
+{
+ struct socket *sock;
+ int new_fd;
+ int error;
+
+ error = security_file_receive(file);
+ if (error)
+ return error;
+
+ new_fd = get_unused_fd_flags(o_flags);
+ if (new_fd < 0)
+ return new_fd;
+
+ error = put_user(new_fd, ufd);
+ if (error) {
+ put_unused_fd(new_fd);
+ return error;
+ }
+
+ /* Bump the usage count and install the file. */
+ sock = sock_from_file(file, &error);
+ if (sock) {
+ sock_update_netprioidx(&sock->sk->sk_cgrp_data);
+ sock_update_classid(&sock->sk->sk_cgrp_data);
+ }
+ fd_install(new_fd, get_file(file));
+ return 0;
+}
+
static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
{
int err = -EBADF;
diff --git a/include/linux/file.h b/include/linux/file.h
index 122f80084a3e..fe18a1a0d555 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -91,6 +91,14 @@ extern void put_unused_fd(unsigned int fd);

extern void fd_install(unsigned int fd, struct file *file);

+extern int __fd_install_received(struct file *file, int __user *ufd,
+ unsigned int o_flags);
+static inline int fd_install_received_user(struct file *file, int __user *ufd,
+ unsigned int o_flags)
+{
+ return __fd_install_received(file, ufd, o_flags);
+}
+
extern void flush_delayed_fput(void);
extern void __fput_sync(struct file *);

diff --git a/include/net/scm.h b/include/net/scm.h
index 581a94d6c613..1ce365f4c256 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -37,7 +37,6 @@ 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 27d477fdcaa0..94f288e8dac5 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -298,7 +298,7 @@ void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm)
int err = 0, i;

for (i = 0; i < fdmax; i++) {
- err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
+ err = fd_install_received_user(scm->fp->fp[i], cmsg_data + i, o_flags);
if (err)
break;
}
diff --git a/net/core/scm.c b/net/core/scm.c
index 6151678c73ed..df190f1fdd28 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -280,36 +280,6 @@ void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_inter
}
EXPORT_SYMBOL(put_cmsg_scm_timestamping);

-int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags)
-{
- struct socket *sock;
- int new_fd;
- int error;
-
- error = security_file_receive(file);
- if (error)
- return error;
-
- new_fd = get_unused_fd_flags(o_flags);
- if (new_fd < 0)
- return new_fd;
-
- error = put_user(new_fd, ufd);
- if (error) {
- put_unused_fd(new_fd);
- return error;
- }
-
- /* Bump the usage count and install the file. */
- sock = sock_from_file(file, &error);
- if (sock) {
- sock_update_netprioidx(&sock->sk->sk_cgrp_data);
- sock_update_classid(&sock->sk->sk_cgrp_data);
- }
- fd_install(new_fd, get_file(file));
- return 0;
-}
-
static int scm_max_fds(struct msghdr *msg)
{
if (msg->msg_controllen <= sizeof(struct cmsghdr))
@@ -336,7 +306,7 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
}

for (i = 0; i < fdmax; i++) {
- err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
+ err = fd_install_received_user(scm->fp->fp[i], cmsg_data + i, o_flags);
if (err)
break;
}
--
2.25.1