- Expose the knob to user space through a proc file /proc/<pid>/setgroups
A value of "deny" means the setgroups system call is disabled in the current processes user namespace and can not be enabled in the future in this user namespace. A value of "allow" means the segtoups system call is enabled. - Descendant user namespaces inherit the value of setgroups from their parents. - A proc file is used (instead of a sysctl) as sysctls currently do not pass in a struct file so file_ns_capable is unusable. Cc: [email protected] Signed-off-by: "Eric W. Biederman" <[email protected]> --- fs/proc/base.c | 31 +++++++++---- include/linux/user_namespace.h | 7 +++ kernel/user.c | 1 + kernel/user_namespace.c | 103 +++++++++++++++++++++++++++++++++++++++++ 4 files changed, 134 insertions(+), 8 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index 772efa45a452..4ebed9f01d97 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2386,7 +2386,7 @@ static int proc_tgid_io_accounting(struct seq_file *m, struct pid_namespace *ns, #endif /* CONFIG_TASK_IO_ACCOUNTING */ #ifdef CONFIG_USER_NS -static int proc_id_map_open(struct inode *inode, struct file *file, +static int proc_userns_open(struct inode *inode, struct file *file, const struct seq_operations *seq_ops) { struct user_namespace *ns = NULL; @@ -2418,7 +2418,7 @@ err: return ret; } -static int proc_id_map_release(struct inode *inode, struct file *file) +static int proc_userns_release(struct inode *inode, struct file *file) { struct seq_file *seq = file->private_data; struct user_namespace *ns = seq->private; @@ -2428,17 +2428,17 @@ static int proc_id_map_release(struct inode *inode, struct file *file) static int proc_uid_map_open(struct inode *inode, struct file *file) { - return proc_id_map_open(inode, file, &proc_uid_seq_operations); + return proc_userns_open(inode, file, &proc_uid_seq_operations); } static int proc_gid_map_open(struct inode *inode, struct file *file) { - return proc_id_map_open(inode, file, &proc_gid_seq_operations); + return proc_userns_open(inode, file, &proc_gid_seq_operations); } static int proc_projid_map_open(struct inode *inode, struct file *file) { - return proc_id_map_open(inode, file, &proc_projid_seq_operations); + return proc_userns_open(inode, file, &proc_projid_seq_operations); } static const struct file_operations proc_uid_map_operations = { @@ -2446,7 +2446,7 @@ static const struct file_operations proc_uid_map_operations = { .write = proc_uid_map_write, .read = seq_read, .llseek = seq_lseek, - .release = proc_id_map_release, + .release = proc_userns_release, }; static const struct file_operations proc_gid_map_operations = { @@ -2454,7 +2454,7 @@ static const struct file_operations proc_gid_map_operations = { .write = proc_gid_map_write, .read = seq_read, .llseek = seq_lseek, - .release = proc_id_map_release, + .release = proc_userns_release, }; static const struct file_operations proc_projid_map_operations = { @@ -2462,7 +2462,20 @@ static const struct file_operations proc_projid_map_operations = { .write = proc_projid_map_write, .read = seq_read, .llseek = seq_lseek, - .release = proc_id_map_release, + .release = proc_userns_release, +}; + +static int proc_setgroups_open(struct inode *inode, struct file *file) +{ + return proc_userns_open(inode, file, &proc_setgroups_seq_operations); +} + +static const struct file_operations proc_setgroups_operations = { + .open = proc_setgroups_open, + .write = proc_setgroups_write, + .read = seq_read, + .llseek = seq_lseek, + .release = proc_userns_release, }; #endif /* CONFIG_USER_NS */ @@ -2572,6 +2585,7 @@ static const struct pid_entry tgid_base_stuff[] = { REG("uid_map", S_IRUGO|S_IWUSR, proc_uid_map_operations), REG("gid_map", S_IRUGO|S_IWUSR, proc_gid_map_operations), REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations), + REG("setgroups", S_IRUGO|S_IWUSR, proc_setgroups_operations), #endif #ifdef CONFIG_CHECKPOINT_RESTORE REG("timers", S_IRUGO, proc_timers_operations), @@ -2913,6 +2927,7 @@ static const struct pid_entry tid_base_stuff[] = { REG("uid_map", S_IRUGO|S_IWUSR, proc_uid_map_operations), REG("gid_map", S_IRUGO|S_IWUSR, proc_gid_map_operations), REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations), + REG("setgroups", S_IRUGO|S_IWUSR, proc_setgroups_operations), #endif }; diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index 8d493083486a..feb0f4ec5573 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -17,6 +17,10 @@ struct uid_gid_map { /* 64 bytes -- 1 cache line */ } extent[UID_GID_MAP_MAX_EXTENTS]; }; +#define USERNS_SETGROUPS_ALLOWED 1UL + +#define USERNS_INIT_FLAGS USERNS_SETGROUPS_ALLOWED + struct user_namespace { struct uid_gid_map uid_map; struct uid_gid_map gid_map; @@ -27,6 +31,7 @@ struct user_namespace { kuid_t owner; kgid_t group; unsigned int proc_inum; + unsigned long flags; /* Register of per-UID persistent keyrings for this namespace */ #ifdef CONFIG_PERSISTENT_KEYRINGS @@ -60,9 +65,11 @@ struct seq_operations; extern const struct seq_operations proc_uid_seq_operations; extern const struct seq_operations proc_gid_seq_operations; extern const struct seq_operations proc_projid_seq_operations; +extern const struct seq_operations proc_setgroups_seq_operations; extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *); extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *); extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *); +extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *); extern bool userns_may_setgroups(const struct user_namespace *ns); #else diff --git a/kernel/user.c b/kernel/user.c index 4efa39350e44..2d09940c9632 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -51,6 +51,7 @@ struct user_namespace init_user_ns = { .owner = GLOBAL_ROOT_UID, .group = GLOBAL_ROOT_GID, .proc_inum = PROC_USER_INIT_INO, + .flags = USERNS_INIT_FLAGS, #ifdef CONFIG_PERSISTENT_KEYRINGS .persistent_keyring_register_sem = __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 44a555ac6104..b507f9af7ff2 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -100,6 +100,11 @@ int create_user_ns(struct cred *new) ns->owner = owner; ns->group = group; + /* Inherit USERNS_SETGROUPS_ALLOWED from our parent */ + mutex_lock(&userns_state_mutex); + ns->flags = parent_ns->flags; + mutex_unlock(&userns_state_mutex); + set_cred_user_ns(new, ns); #ifdef CONFIG_PERSISTENT_KEYRINGS @@ -839,6 +844,102 @@ static bool new_idmap_permitted(const struct file *file, return false; } +static void *setgroups_m_start(struct seq_file *seq, loff_t *ppos) +{ + struct user_namespace *ns = seq->private; + + return (*ppos == 0) ? ns : NULL; +} + +static void *setgroups_m_next(struct seq_file *seq, void *v, loff_t *ppos) +{ + ++*ppos; + return NULL; +} + +static void setgroups_m_stop(struct seq_file *seq, void *v) +{ +} + +static int setgroups_m_show(struct seq_file *seq, void *v) +{ + struct user_namespace *ns = seq->private; + + seq_printf(seq, "%s\n", + test_bit(USERNS_SETGROUPS_ALLOWED, &ns->flags) ? + "allow" : "deny"); + return 0; +} + +const struct seq_operations proc_setgroups_seq_operations = { + .start = setgroups_m_start, + .stop = setgroups_m_stop, + .next = setgroups_m_next, + .show = setgroups_m_show, +}; + +ssize_t proc_setgroups_write(struct file *file, const char __user *buf, + size_t count, loff_t *ppos) +{ + struct seq_file *seq = file->private_data; + struct user_namespace *ns = seq->private; + char kbuf[8], *pos; + bool setgroups_allowed; + ssize_t ret; + + ret = -EACCES; + if (!file_ns_capable(file, ns, CAP_SYS_ADMIN)) + goto out; + + /* Only allow a very narrow range of strings to be written */ + ret = -EINVAL; + if ((*ppos != 0) || (count >= sizeof(kbuf))) + goto out; + + /* What was written? */ + ret = -EFAULT; + if (copy_from_user(kbuf, buf, count)) + goto out; + kbuf[count] = '\0'; + pos = kbuf; + + /* What is being requested? */ + ret = -EINVAL; + if (strncmp(pos, "allow", 5) == 0) { + pos += 5; + setgroups_allowed = true; + } + else if (strncmp(pos, "deny", 4) == 0) { + pos += 4; + setgroups_allowed = false; + } + else + goto out; + + /* Verify there is not trailing junk on the line */ + pos = skip_spaces(pos); + if (*pos != '\0') + goto out; + + mutex_lock(&userns_state_mutex); + if (setgroups_allowed) { + ret = -EPERM; + if (!(ns->flags & USERNS_SETGROUPS_ALLOWED)) { + mutex_unlock(&userns_state_mutex); + goto out; + } + } else { + ns->flags &= ~USERNS_SETGROUPS_ALLOWED; + } + mutex_unlock(&userns_state_mutex); + + /* Report a successful write */ + *ppos = count; + ret = count; +out: + return ret; +} + bool userns_may_setgroups(const struct user_namespace *ns) { bool allowed; @@ -848,6 +949,8 @@ bool userns_may_setgroups(const struct user_namespace *ns) * the user namespace has been established. */ allowed = ns->gid_map.nr_extents != 0; + /* Is setgroups allowed? */ + allowed = allowed && (ns->flags & USERNS_SETGROUPS_ALLOWED); mutex_unlock(&userns_state_mutex); return allowed; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
