[PATCH v4 05/11] fs: Expand __fd_install_received() to accept fd

Kees Cook
2020-06-16T03:26:45Z

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, 23 insertions(+), 9 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 14a8ef74efb2..b583e7c60571 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -950,8 +950,8 @@ 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, bool ufd_required, int __user *ufd,
- unsigned int o_flags)
+int __fd_install_received(int fd, struct file *file, bool ufd_required,
+ int __user *ufd, unsigned int o_flags)
{
struct socket *sock;
int new_fd;
@@ -961,9 +961,11 @@ int __fd_install_received(struct file *file, bool ufd_required, int __user *ufd,
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_required) {
error = put_user(new_fd, ufd);
@@ -973,6 +975,15 @@ int __fd_install_received(struct file *file, bool ufd_required, int __user *ufd,
}
}

+ 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.
@@ -982,7 +993,6 @@ int __fd_install_received(struct file *file, bool ufd_required, int __user *ufd,
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 999a2c56db07..f1d16e24a12e 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -91,16 +91,20 @@ 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, bool ufd_required,
+extern int __fd_install_received(int fd, struct file *file, bool ufd_required,
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, true, ufd, o_flags);
+ return __fd_install_received(-1, file, true, ufd, o_flags);
}
static inline int fd_install_received(struct file *file, unsigned int o_flags)
{
- return __fd_install_received(file, false, NULL, o_flags);
+ return __fd_install_received(-1, file, false, NULL, o_flags);
+}
+static inline int fd_replace_received(int fd, struct file *file, unsigned int o_flags)
+{
+ return __fd_install_received(fd, file, false, NULL, o_flags);
}

extern void flush_delayed_fput(void);
--
2.25.1