Commit 0097875b authored by Eric W. Biederman's avatar Eric W. Biederman

proc: Implement /proc/thread-self to point at the directory of the current thread

/proc/thread-self is derived from /proc/self.  /proc/thread-self
points to the directory in proc containing information about the
current thread.

This funtionality has been missing for a long time, and is tricky to
implement in userspace as gettid() is not exported by glibc.  More
importantly this allows fixing defects in /proc/mounts and /proc/net
where in a threaded application today they wind up being empty files
when only the initial pthread has exited, causing problems for other
threads.
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 6ba8ed79
......@@ -23,6 +23,7 @@ proc-y += version.o
proc-y += softirqs.o
proc-y += namespaces.o
proc-y += self.o
proc-y += thread_self.o
proc-$(CONFIG_PROC_SYSCTL) += proc_sysctl.o
proc-$(CONFIG_NET) += proc_net.o
proc-$(CONFIG_PROC_KCORE) += kcore.o
......
......@@ -2847,7 +2847,7 @@ static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter ite
return iter;
}
#define TGID_OFFSET (FIRST_PROCESS_ENTRY + 1)
#define TGID_OFFSET (FIRST_PROCESS_ENTRY + 2)
/* for the /proc/ directory itself, after non-process stuff has been done */
int proc_pid_readdir(struct file *file, struct dir_context *ctx)
......@@ -2859,14 +2859,19 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
if (pos >= PID_MAX_LIMIT + TGID_OFFSET)
return 0;
if (pos == TGID_OFFSET - 1) {
if (pos == TGID_OFFSET - 2) {
struct inode *inode = ns->proc_self->d_inode;
if (!dir_emit(ctx, "self", 4, inode->i_ino, DT_LNK))
return 0;
iter.tgid = 0;
} else {
iter.tgid = pos - TGID_OFFSET;
ctx->pos = pos = pos + 1;
}
if (pos == TGID_OFFSET - 1) {
struct inode *inode = ns->proc_thread_self->d_inode;
if (!dir_emit(ctx, "thread-self", 11, inode->i_ino, DT_LNK))
return 0;
ctx->pos = pos = pos + 1;
}
iter.tgid = pos - TGID_OFFSET;
iter.task = NULL;
for (iter = next_tgid(ns, iter);
iter.task;
......
......@@ -442,6 +442,7 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
int proc_fill_super(struct super_block *s)
{
struct inode *root_inode;
int ret;
s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
s->s_blocksize = 1024;
......@@ -463,5 +464,9 @@ int proc_fill_super(struct super_block *s)
return -ENOMEM;
}
return proc_setup_self(s);
ret = proc_setup_self(s);
if (ret) {
return ret;
}
return proc_setup_thread_self(s);
}
......@@ -233,6 +233,12 @@ static inline int proc_net_init(void) { return 0; }
*/
extern int proc_setup_self(struct super_block *);
/*
* proc_thread_self.c
*/
extern int proc_setup_thread_self(struct super_block *);
extern void proc_thread_self_init(void);
/*
* proc_sysctl.c
*/
......
......@@ -149,6 +149,8 @@ static void proc_kill_sb(struct super_block *sb)
ns = (struct pid_namespace *)sb->s_fs_info;
if (ns->proc_self)
dput(ns->proc_self);
if (ns->proc_thread_self)
dput(ns->proc_thread_self);
kill_anon_super(sb);
put_pid_ns(ns);
}
......@@ -170,6 +172,7 @@ void __init proc_root_init(void)
return;
proc_self_init();
proc_thread_self_init();
proc_symlink("mounts", NULL, "self/mounts");
proc_net_init();
......
#include <linux/sched.h>
#include <linux/namei.h>
#include <linux/slab.h>
#include <linux/pid_namespace.h>
#include "internal.h"
/*
* /proc/thread_self:
*/
static int proc_thread_self_readlink(struct dentry *dentry, char __user *buffer,
int buflen)
{
struct pid_namespace *ns = dentry->d_sb->s_fs_info;
pid_t tgid = task_tgid_nr_ns(current, ns);
pid_t pid = task_pid_nr_ns(current, ns);
char tmp[PROC_NUMBUF + 6 + PROC_NUMBUF];
if (!pid)
return -ENOENT;
sprintf(tmp, "%d/task/%d", tgid, pid);
return readlink_copy(buffer, buflen, tmp);
}
static void *proc_thread_self_follow_link(struct dentry *dentry, struct nameidata *nd)
{
struct pid_namespace *ns = dentry->d_sb->s_fs_info;
pid_t tgid = task_tgid_nr_ns(current, ns);
pid_t pid = task_pid_nr_ns(current, ns);
char *name = ERR_PTR(-ENOENT);
if (pid) {
name = kmalloc(PROC_NUMBUF + 6 + PROC_NUMBUF, GFP_KERNEL);
if (!name)
name = ERR_PTR(-ENOMEM);
else
sprintf(name, "%d/task/%d", tgid, pid);
}
nd_set_link(nd, name);
return NULL;
}
static const struct inode_operations proc_thread_self_inode_operations = {
.readlink = proc_thread_self_readlink,
.follow_link = proc_thread_self_follow_link,
.put_link = kfree_put_link,
};
static unsigned thread_self_inum;
int proc_setup_thread_self(struct super_block *s)
{
struct inode *root_inode = s->s_root->d_inode;
struct pid_namespace *ns = s->s_fs_info;
struct dentry *thread_self;
mutex_lock(&root_inode->i_mutex);
thread_self = d_alloc_name(s->s_root, "thread-self");
if (thread_self) {
struct inode *inode = new_inode_pseudo(s);
if (inode) {
inode->i_ino = thread_self_inum;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
inode->i_mode = S_IFLNK | S_IRWXUGO;
inode->i_uid = GLOBAL_ROOT_UID;
inode->i_gid = GLOBAL_ROOT_GID;
inode->i_op = &proc_thread_self_inode_operations;
d_add(thread_self, inode);
} else {
dput(thread_self);
thread_self = ERR_PTR(-ENOMEM);
}
} else {
thread_self = ERR_PTR(-ENOMEM);
}
mutex_unlock(&root_inode->i_mutex);
if (IS_ERR(thread_self)) {
pr_err("proc_fill_super: can't allocate /proc/thread_self\n");
return PTR_ERR(thread_self);
}
ns->proc_thread_self = thread_self;
return 0;
}
void __init proc_thread_self_init(void)
{
proc_alloc_inum(&thread_self_inum);
}
......@@ -33,6 +33,7 @@ struct pid_namespace {
#ifdef CONFIG_PROC_FS
struct vfsmount *proc_mnt;
struct dentry *proc_self;
struct dentry *proc_thread_self;
#endif
#ifdef CONFIG_BSD_PROCESS_ACCT
struct bsd_acct_struct *bacct;
......
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