On Mon, Jul 06, 2020 at 01:17:18PM -0700, Kees Cook wrote:
Expand __receive_fd() with support for replace_fd() for the coming seccomp "addfd" ioctl(). Add new wrapper receive_fd_replace() for the new behavior and update existing wrappers to retain old behavior.
Thanks to Colin Ian King colin.king@canonical.com for pointing out an uninitialized variable exposure in an earlier version of this patch.
Reviewed-by: Sargun Dhillon sargun@sargun.me Signed-off-by: Kees Cook keescook@chromium.org
Thanks! (One tiny-nit below.) Acked-by: Christian Brauner christian.brauner@ubuntu.com
fs/file.c | 24 ++++++++++++++++++------ include/linux/file.h | 10 +++++++--- 2 files changed, 25 insertions(+), 9 deletions(-)
diff --git a/fs/file.c b/fs/file.c index 0efdcf413210..11313ff36802 100644 --- a/fs/file.c +++ b/fs/file.c @@ -937,6 +937,7 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags) /**
- __receive_fd() - 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
@@ -950,7 +951,7 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
- Returns newly install fd or -ve on error.
*/ -int __receive_fd(struct file *file, int __user *ufd, unsigned int o_flags) +int __receive_fd(int fd, struct file *file, int __user *ufd, unsigned int o_flags) { struct socket *sock; int new_fd; @@ -960,18 +961,30 @@ int __receive_fd(struct file *file, int __user *ufd, unsigned int o_flags) 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;- } else
new_fd = fd;
This is nitpicky but coding style technically wants us to use braces around both branches if one of them requires them. ;)
if (ufd) { error = put_user(new_fd, ufd); if (error) {
put_unused_fd(new_fd);
if (fd < 0)put_unused_fd(new_fd); return error;
- if (fd < 0)
fd_install(new_fd, get_file(file));- else {
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
@@ -982,7 +995,6 @@ int __receive_fd(struct file *file, int __user *ufd, unsigned int o_flags) 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 d9fee9f5c8da..225982792fa2 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 __receive_fd(struct file *file, int __user *ufd, +extern int __receive_fd(int fd, struct file *file, int __user *ufd, unsigned int o_flags); static inline int receive_fd_user(struct file *file, int __user *ufd, unsigned int o_flags) { if (ufd == NULL) return -EFAULT;
- return __receive_fd(file, ufd, o_flags);
- return __receive_fd(-1, file, ufd, o_flags);
} static inline int receive_fd(struct file *file, unsigned int o_flags) {
- return __receive_fd(file, NULL, o_flags);
- return __receive_fd(-1, file, NULL, o_flags);
+} +static inline int receive_fd_replace(int fd, struct file *file, unsigned int o_flags) +{
- return __receive_fd(fd, file, NULL, o_flags);
} extern void flush_delayed_fput(void); -- 2.25.1