[PATCH v7 7/9] fs: Expand __receive_fd() to accept existing fd
From: Kees Cook <hidden>
Date: 2020-07-09 18:27:01
Also in:
linux-fsdevel, linux-kselftest, lkml, netdev
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
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 [off-list ref] for pointing out an uninitialized variable exposure in an earlier version of this patch. Reviewed-by: Sargun Dhillon <redacted> Acked-by: Christian Brauner <redacted> Signed-off-by: Kees Cook <redacted> --- fs/file.c | 25 +++++++++++++++++++------ include/linux/file.h | 10 +++++++--- 2 files changed, 26 insertions(+), 9 deletions(-)
diff --git a/fs/file.c b/fs/file.c
index 87954bab9306..feebdc17bf46 100644
--- a/fs/file.c
+++ b/fs/file.c@@ -935,6 +935,7 @@ 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
@@ -948,7 +949,7 @@ 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) { int new_fd; int error;
@@ -957,21 +958,33 @@ 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; + } 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 sock usage counts, if any. */ __receive_sock(file); - 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