[PATCH v5 5/7] fs: Expand __fd_install_received() to accept fd

Kees Cook
2020-06-17T22:03:59Z

Expand __fd_install_received() with support for replace_fd() for the
coming seccomp "addfd" ioctl(). Add new wrapper fd_replace_received()
for the new mode and update existing wrappers to retain old mode.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
fs/file.c | 22 +++++++++++++++++-----
include/linux/file.h | 10 +++++++---
2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index de85a42defe2..9568bcfd1f44 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -937,6 +937,7 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
/**
* __fd_install_received() - Install received file into file descriptor table
*
+ * @fd: fd to install into (if negative, a new fd will be allocated)
* @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
@@ -947,7 +948,8 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
*
* Returns newly install fd or -ve on error.
*/
-int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_flags)
+int __fd_install_received(int fd, struct file *file, int __user *ufd,
+ unsigned int o_flags)
{
struct socket *sock;
int new_fd;
@@ -957,9 +959,11 @@ int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_fla
if (error)
return error;

- new_fd = get_unused_fd_flags(o_flags);
- if (new_fd < 0)
- return new_fd;
+ if (fd < 0) {
+ new_fd = get_unused_fd_flags(o_flags);
+ if (new_fd < 0)
+ return new_fd;
+ }

if (ufd) {
error = put_user(new_fd, ufd);
@@ -969,6 +973,15 @@ int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_fla
}
}

+ if (fd < 0)
+ fd_install(new_fd, get_file(file));
+ else {
+ new_fd = fd;
+ error = replace_fd(new_fd, file, o_flags);
+ if (error)
+ return error;
+ }
+
/* Bump the usage count and install the file. The resulting value of
* "error" is ignored here since we only need to take action when
* the file is a socket and testing "sock" for NULL is sufficient.
@@ -978,7 +991,6 @@ int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_fla
sock_update_netprioidx(&sock->sk->sk_cgrp_data);
sock_update_classid(&sock->sk->sk_cgrp_data);
}
- fd_install(new_fd, get_file(file));
return new_fd;
}

diff --git a/include/linux/file.h b/include/linux/file.h
index e19974ed9322..04389b0da11b 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -92,18 +92,22 @@ 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,
+extern int __fd_install_received(int fd, 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)
{
if (ufd == NULL)
return -EFAULT;
- return __fd_install_received(file, ufd, o_flags);
+ return __fd_install_received(-1, file, ufd, o_flags);
}
static inline int fd_install_received(struct file *file, unsigned int o_flags)
{
- return __fd_install_received(file, NULL, o_flags);
+ return __fd_install_received(-1, file, NULL, o_flags);
+}
+static inline int fd_replace_received(int fd, struct file *file, unsigned int o_flags)
+{
+ return __fd_install_received(fd, file, NULL, o_flags);
}

extern void flush_delayed_fput(void);
--
2.25.1