cgroup: make cgroup_path() and friends behave in the style of strlcpy()

cgroup_path() and friends used to format the path from the end and
thus the resulting path usually didn't start at the start of the
passed in buffer.  Also, when the buffer was too small, the partial
result was truncated from the head rather than tail and there was no
way to tell how long the full path would be.  These make the functions
less robust and more awkward to use.

With recent updates to kernfs_path(), cgroup_path() and friends can be
made to behave in strlcpy() style.

* cgroup_path(), cgroup_path_ns[_locked]() and task_cgroup_path() now
  always return the length of the full path.  If buffer is too small,
  it contains nul terminated truncated output.

* All users updated accordingly.

v2: cgroup_path() usage in kernel/sched/debug.c converted.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Peter Zijlstra <peterz@infradead.org>

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 10648e300c930ecb06c58371a6c3822a1192d229..4e8c215e185c1dffe6b59541b32848e18f864937 100644 (file)
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -343,16 +343,7 @@ static inline struct blkcg *cpd_to_blkcg(struct blkcg_policy_data *cpd)
  */
 static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
 {
-       char *p;
-
-       p = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
-       if (!p) {
-               strncpy(buf, "<unavailable>", buflen);
-               return -ENAMETOOLONG;
-       }
-
-       memmove(buf, p, buf + buflen - p);
-       return 0;
+       return cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
 }
 
 /**

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 5a9abdee43fe839ff6acd2a50504bcc34696eaa2..6df36361a492405644c9a4c61ba01d14ceeb9d29 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -97,7 +97,7 @@ int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_rm_cftypes(struct cftype *cfts);
 void cgroup_file_notify(struct cgroup_file *cfile);
 
-char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
+int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
                     struct pid *pid, struct task_struct *tsk);
@@ -538,15 +538,9 @@ static inline int cgroup_name(struct cgroup *cgrp, char *buf, size_t buflen)
        return kernfs_name(cgrp->kn, buf, buflen);
 }
 
-static inline char * __must_check cgroup_path(struct cgroup *cgrp, char *buf,
-                                             size_t buflen)
+static inline int cgroup_path(struct cgroup *cgrp, char *buf, size_t buflen)
 {
-       int ret;
-
-       ret = kernfs_path(cgrp->kn, buf, buflen);
-       if (ret < 0 || ret >= buflen)
-               return NULL;
-       return buf;
+       return kernfs_path(cgrp->kn, buf, buflen);
 }
 
 static inline void pr_cont_cgroup_name(struct cgroup *cgrp)
@@ -639,8 +633,8 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
                                        struct user_namespace *user_ns,
                                        struct cgroup_namespace *old_ns);
 
-char *cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
-                    struct cgroup_namespace *ns);
+int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
+                  struct cgroup_namespace *ns);
 
 #else /* !CONFIG_CGROUPS */
 

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d1c51b7f5221fbfbb85ed3d12e4918a970713829..3861161e460f961f0659911a890220c8d9778f8d 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2315,22 +2315,18 @@ static struct file_system_type cgroup2_fs_type = {
        .fs_flags = FS_USERNS_MOUNT,
 };
 
-static char *cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
-                                  struct cgroup_namespace *ns)
+static int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
+                                struct cgroup_namespace *ns)
 {
        struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
-       int ret;
 
-       ret = kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
-       if (ret < 0 || ret >= buflen)
-               return NULL;
-       return buf;
+       return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
 }
 
-char *cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
-                    struct cgroup_namespace *ns)
+int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
+                  struct cgroup_namespace *ns)
 {
-       char *ret;
+       int ret;
 
        mutex_lock(&cgroup_mutex);
        spin_lock_irq(&css_set_lock);
@@ -2357,12 +2353,12 @@ EXPORT_SYMBOL_GPL(cgroup_path_ns);
  *
  * Return value is the same as kernfs_path().
  */
-char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
+int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 {
        struct cgroup_root *root;
        struct cgroup *cgrp;
        int hierarchy_id = 1;
-       char *path = NULL;
+       int ret;
 
        mutex_lock(&cgroup_mutex);
        spin_lock_irq(&css_set_lock);
@@ -2371,16 +2367,15 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 
        if (root) {
                cgrp = task_cgroup_from_root(task, root);
-               path = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
+               ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
        } else {
                /* if no hierarchy exists, everyone is in "/" */
-               if (strlcpy(buf, "/", buflen) < buflen)
-                       path = buf;
+               ret = strlcpy(buf, "/", buflen);
        }
 
        spin_unlock_irq(&css_set_lock);
        mutex_unlock(&cgroup_mutex);
-       return path;
+       return ret;
 }
 EXPORT_SYMBOL_GPL(task_cgroup_path);
 
@@ -5716,7 +5711,7 @@ core_initcall(cgroup_wq_init);
 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
                     struct pid *pid, struct task_struct *tsk)
 {
-       char *buf, *path;
+       char *buf;
        int retval;
        struct cgroup_root *root;
 
@@ -5759,18 +5754,18 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
                 * " (deleted)" is appended to the cgroup path.
                 */
                if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
-                       path = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
+                       retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
                                                current->nsproxy->cgroup_ns);
-                       if (!path) {
+                       if (retval >= PATH_MAX) {
                                retval = -ENAMETOOLONG;
                                goto out_unlock;
                        }
+
+                       seq_puts(m, buf);
                } else {
-                       path = "/";
+                       seq_puts(m, "/");
                }
 
-               seq_puts(m, path);
-
                if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
                        seq_puts(m, " (deleted)\n");
                else
@@ -6035,8 +6030,9 @@ static void cgroup_release_agent(struct work_struct *work)
 {
        struct cgroup *cgrp =
                container_of(work, struct cgroup, release_agent_work);
-       char *pathbuf = NULL, *agentbuf = NULL, *path;
+       char *pathbuf = NULL, *agentbuf = NULL;
        char *argv[3], *envp[3];
+       int ret;
 
        mutex_lock(&cgroup_mutex);
 
@@ -6046,13 +6042,13 @@ static void cgroup_release_agent(struct work_struct *work)
                goto out;
 
        spin_lock_irq(&css_set_lock);
-       path = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
+       ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
        spin_unlock_irq(&css_set_lock);
-       if (!path)
+       if (ret >= PATH_MAX)
                goto out;
 
        argv[0] = agentbuf;
-       argv[1] = path;
+       argv[1] = pathbuf;
        argv[2] = NULL;
 
        /* minimal command environment */

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index c7fd2778ed50edc52b7c0e5f1f651dcb141c9495..793ae6fd96dcd2118f410a4c6813d257b05d84da 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2689,7 +2689,7 @@ void __cpuset_memory_pressure_bump(void)
 int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
                     struct pid *pid, struct task_struct *tsk)
 {
-       char *buf, *p;
+       char *buf;
        struct cgroup_subsys_state *css;
        int retval;
 
@@ -2700,18 +2700,18 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
 
        retval = -ENAMETOOLONG;
        css = task_get_css(tsk, cpuset_cgrp_id);
-       p = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
-                          current->nsproxy->cgroup_ns);
+       retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
+                               current->nsproxy->cgroup_ns);
        css_put(css);
-       if (!p)
+       if (retval >= PATH_MAX)
                goto out_free;
-       seq_puts(m, p);
+       seq_puts(m, buf);
        seq_putc(m, '\n');
        retval = 0;
 out_free:
        kfree(buf);
 out:
-       return retval;
+       return 0;
 }
 #endif /* CONFIG_PROC_PID_CPUSET */
 

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 2a0a9995256d9e920d3c94cf944cd6acb61fa627..23cb609ba4ebce1b71d326a1f3aba7f0dd8bfd55 100644 (file)
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -410,7 +410,8 @@ static char *task_group_path(struct task_group *tg)
        if (autogroup_path(tg, group_path, PATH_MAX))
                return group_path;
 
-       return cgroup_path(tg->css.cgroup, group_path, PATH_MAX);
+       cgroup_path(tg->css.cgroup, group_path, PATH_MAX);
+       return group_path;
 }
 #endif