Record a conservative executable identity key when a template is created: device, inode, size, mode, owner, ctime, and mtime. Recheck it before each spawn. For path-created templates, also reopen the path so a replaced executable cannot silently reuse the old template fd. Reject stale templates with ESTALE. Keep the check conservative by also rechecking that the file remains a regular executable mapping target.
Signed-off-by: Li Chen <[email protected]> --- MAINTAINERS | 1 + fs/spawn_template.c | 75 ++++++++++++++++++++++++++++++++++ include/linux/spawn_template.h | 25 ++++++++++++ 3 files changed, 101 insertions(+) create mode 100644 include/linux/spawn_template.h diff --git a/MAINTAINERS b/MAINTAINERS index d5441812825c3..ea4134a188779 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -9737,6 +9737,7 @@ F: fs/tests/binfmt_*_kunit.c F: fs/tests/exec_kunit.c F: include/linux/binfmts.h F: include/linux/elf.h +F: include/linux/spawn_template.h F: include/uapi/linux/auxvec.h F: include/uapi/linux/binfmts.h F: include/uapi/linux/elf.h diff --git a/fs/spawn_template.c b/fs/spawn_template.c index 8c3711929cffb..268f804227987 100644 --- a/fs/spawn_template.c +++ b/fs/spawn_template.c @@ -15,6 +15,7 @@ #include <linux/sched/task.h> #include <linux/signal.h> #include <linux/slab.h> +#include <linux/spawn_template.h> #include <linux/string.h> #include <linux/syscalls.h> #include <linux/uaccess.h> @@ -27,6 +28,7 @@ struct spawn_template { struct file *exec_file; + struct spawn_template_file_key exec_key; const struct cred *creator_cred; char *filename; bool deny_write; @@ -40,6 +42,46 @@ struct spawn_template_spawn_context { static const struct file_operations spawn_template_fops; +static bool spawn_template_file_exec_allowed(struct file *file); + +void spawn_template_fill_file_key(struct file *file, + struct spawn_template_file_key *key) +{ + struct inode *inode = file_inode(file); + struct timespec64 ctime = inode_get_ctime(inode); + struct timespec64 mtime = inode_get_mtime(inode); + + key->dev = inode->i_sb->s_dev; + key->ino = inode->i_ino; + key->size = i_size_read(inode); + key->mode = READ_ONCE(inode->i_mode); + key->uid = inode->i_uid; + key->gid = inode->i_gid; + key->ctime_sec = ctime.tv_sec; + key->ctime_nsec = ctime.tv_nsec; + key->mtime_sec = mtime.tv_sec; + key->mtime_nsec = mtime.tv_nsec; +} + +bool spawn_template_file_key_matches(struct file *file, + const struct spawn_template_file_key *key) +{ + struct spawn_template_file_key cur; + + spawn_template_fill_file_key(file, &cur); + + return cur.dev == key->dev && + cur.ino == key->ino && + cur.size == key->size && + cur.mode == key->mode && + uid_eq(cur.uid, key->uid) && + gid_eq(cur.gid, key->gid) && + cur.ctime_sec == key->ctime_sec && + cur.ctime_nsec == key->ctime_nsec && + cur.mtime_sec == key->mtime_sec && + cur.mtime_nsec == key->mtime_nsec; +} + static int spawn_template_exit_status(int err) { switch (err) { @@ -58,6 +100,32 @@ static bool spawn_template_cred_matches(struct spawn_template *tmpl) return current_cred() == tmpl->creator_cred; } +static bool spawn_template_key_matches(struct spawn_template *tmpl) +{ + bool matches; + + if (tmpl->filename) { + struct file *file __free(fput) = NULL; + struct file *tmp; + + tmp = open_exec(tmpl->filename); + if (IS_ERR(tmp)) + return false; + file = tmp; + + matches = spawn_template_file_key_matches(file, + &tmpl->exec_key); + matches = matches && spawn_template_file_exec_allowed(file); + exe_file_allow_write_access(file); + if (!matches) + return false; + } + + return spawn_template_file_exec_allowed(tmpl->exec_file) && + spawn_template_file_key_matches(tmpl->exec_file, + &tmpl->exec_key); +} + static int spawn_template_copy_signal_set(const struct spawn_template_action *action, sigset_t *mask) { @@ -433,6 +501,7 @@ SYSCALL_DEFINE2(spawn_template_create, &tmpl->deny_write); if (ret) goto out_free_tmpl; + spawn_template_fill_file_key(tmpl->exec_file, &tmpl->exec_key); if (args.flags & SPAWN_TEMPLATE_CREATE_CLOEXEC) fd_flags |= O_CLOEXEC; @@ -507,6 +576,11 @@ SYSCALL_DEFINE3(spawn_template_spawn, int, template_fd, if (ret) goto out_free_ctx; + if (!spawn_template_key_matches(ctx->tmpl)) { + ret = -ESTALE; + goto out_free_actions; + } + kargs = (struct kernel_clone_args) { .flags = CLONE_VM | CLONE_VFORK | CLONE_PIDFD, .pidfd = u64_to_user_ptr(ctx->args.pidfd), @@ -517,6 +591,7 @@ SYSCALL_DEFINE3(spawn_template_spawn, int, template_fd, ret = kernel_clone(&kargs); +out_free_actions: kfree(ctx->actions); out_free_ctx: kfree(ctx); diff --git a/include/linux/spawn_template.h b/include/linux/spawn_template.h new file mode 100644 index 0000000000000..f14a7749fe55b --- /dev/null +++ b/include/linux/spawn_template.h @@ -0,0 +1,25 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_SPAWN_TEMPLATE_H +#define _LINUX_SPAWN_TEMPLATE_H + +#include <linux/fs.h> + +struct spawn_template_file_key { + dev_t dev; + ino_t ino; + loff_t size; + umode_t mode; + kuid_t uid; + kgid_t gid; + u64 ctime_sec; + u64 ctime_nsec; + u64 mtime_sec; + u64 mtime_nsec; +}; + +void spawn_template_fill_file_key(struct file *file, + struct spawn_template_file_key *key); +bool spawn_template_file_key_matches(struct file *file, + const struct spawn_template_file_key *key); + +#endif /* _LINUX_SPAWN_TEMPLATE_H */ -- 2.52.0
