From 20370a5f5d9b1549ab3bf10a898b4e024b8841fa Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 24 Jul 2026 15:41:19 +0200 Subject: fs: add fchroot() Add a file descriptor based counterpart to chroot(2). This has been overdue for a long time. It is the natural companion to fchdir() and avoids re-resolving a path that the caller already holds a file descriptor to. No TOCTOU between resolving the target and changing the root. It composes with modern fd-based APIs meaning it works with O_PATH file descriptors and file descriptors to detached mount trees created via open_tree(OPEN_TREE_CLONE). The permission model is identical to chroot(2). The caller must have CAP_SYS_CHROOT in its user namespace, must pass MAY_EXEC | MAY_CHDIR permission checks on the target directory, and LSMs are consulted via the same security_path_chroot() hook. The system call takes a flags argument for future extensibility which must currently be zero. Link: https://patch.msgid.link/20260724-work-failfs-v2-3-485dabbae185@kernel.org Signed-off-by: Christian Brauner (Amutable) --- include/linux/syscalls.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 874d9067a43b..8413b624ad47 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -457,6 +457,7 @@ asmlinkage long sys_faccessat2(int dfd, const char __user *filename, int mode, asmlinkage long sys_chdir(const char __user *filename); asmlinkage long sys_fchdir(unsigned int fd); asmlinkage long sys_chroot(const char __user *filename); +asmlinkage long sys_fchroot(int fd, unsigned int flags); asmlinkage long sys_fchmod(unsigned int fd, umode_t mode); asmlinkage long sys_fchmodat(int dfd, const char __user *filename, umode_t mode); -- cgit v1.2.3