This patchset implements /proc/thread-self a magic symlink that
solves a couple of problems.
- It makes it easy to get to a specific threads directory in /proc
with gettid() not being exported in glibc this is currently a pain.
- It allows fixing the problem present in /proc/mounts and /proc/net
that when the thread group leader exits but the entire thread group
remains /proc/self/net and /proc/self/mounts and thus /proc/mounts and
/proc/net become empty.
- As mount and network namespaces are per thread it allows /proc/net and
/proc/mounts to reflect this.
This is small chance changing /proc/net and /proc/mounts will cause
userspace regressions (although nothing has shown up in my testing) if
that happens we can just point the change that moves them from
/proc/self/... to /proc/thread-self/...
Eric W. Biederman (4):
proc: Have net show up under /proc/<tgid>/task/<tid>
proc: Implement /proc/thread-self to point at the directory of the current thread
proc: Point /proc/net at /proc/thread-self/net instead of /proc/self/net
proc: Point /proc/mounts at /proc/thread-self/mounts instead of /proc/self/mounts
fs/proc/Makefile | 1 +
fs/proc/base.c | 18 ++++++---
fs/proc/inode.c | 7 +++-
fs/proc/internal.h | 6 +++
fs/proc/proc_net.c | 2 +-
fs/proc/root.c | 5 ++-
fs/proc/thread_self.c | 85 +++++++++++++++++++++++++++++++++++++++++++
include/linux/pid_namespace.h | 1 +
8 files changed, 117 insertions(+), 8 deletions(-)
Eric
Network namespaces are per task so it make sense for them to show up
in the task directory.
Signed-off-by: "Eric W. Biederman" <[email protected]>
---
fs/proc/base.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 2d696b0c93bf..ed34e405c6b9 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2895,6 +2895,9 @@ static const struct pid_entry tid_base_stuff[] = {
DIR("fd", S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
DIR("fdinfo", S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
DIR("ns", S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
+#ifdef CONFIG_NET
+ DIR("net", S_IRUGO|S_IXUGO, proc_net_inode_operations, proc_net_operations),
+#endif
REG("environ", S_IRUSR, proc_environ_operations),
INF("auxv", S_IRUSR, proc_pid_auxv),
ONE("status", S_IRUGO, proc_pid_status),
--
1.9.1
/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: "Eric W. Biederman" <[email protected]>
---
fs/proc/Makefile | 1 +
fs/proc/base.c | 15 +++++---
fs/proc/inode.c | 7 +++-
fs/proc/internal.h | 6 +++
fs/proc/root.c | 3 ++
fs/proc/thread_self.c | 85 +++++++++++++++++++++++++++++++++++++++++++
include/linux/pid_namespace.h | 1 +
7 files changed, 112 insertions(+), 6 deletions(-)
create mode 100644 fs/proc/thread_self.c
diff --git a/fs/proc/Makefile b/fs/proc/Makefile
index 239493ec718e..7151ea428041 100644
--- a/fs/proc/Makefile
+++ b/fs/proc/Makefile
@@ -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
diff --git a/fs/proc/base.c b/fs/proc/base.c
index ed34e405c6b9..0131156ce7c9 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2847,7 +2847,7 @@ retry:
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;
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 0adbc02d60e3..333080d7a671 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -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);
}
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 3ab6d14e71c5..ee04619173b2 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -234,6 +234,12 @@ 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
*/
#ifdef CONFIG_PROC_SYSCTL
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 5dbadecb234d..48f1c03bc7ed 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.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();
diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
new file mode 100644
index 000000000000..59075b509df3
--- /dev/null
+++ b/fs/proc/thread_self.c
@@ -0,0 +1,85 @@
+#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);
+}
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 7246ef3d4455..1997ffc295a7 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -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;
--
1.9.1
In oddball cases where the thread has a different network namespace
than the primary thread group leader or more likely in cases where
the thread remains and the thread group leader has exited this
ensures that /proc/net continues to work.
This should not cause any problems but if it does this patch can just
be reverted.
Signed-off-by: "Eric W. Biederman" <[email protected]>
---
fs/proc/proc_net.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index a63af3e0a612..39481028ec08 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -226,7 +226,7 @@ static struct pernet_operations __net_initdata proc_net_ns_ops = {
int __init proc_net_init(void)
{
- proc_symlink("net", NULL, "self/net");
+ proc_symlink("net", NULL, "thread-self/net");
return register_pernet_subsys(&proc_net_ns_ops);
}
--
1.9.1
In oddball cases where the thread has a different mount namespace than
the thread group leader or more likely in cases where the thread
remains and the thread group leader has exited this ensures that
/proc/mounts continues to work.
This should not cause any problems but if it does this patch can just
be reverted.
Signed-off-by: "Eric W. Biederman" <[email protected]>
---
fs/proc/root.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 48f1c03bc7ed..92c12c243ce3 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -173,7 +173,7 @@ void __init proc_root_init(void)
proc_self_init();
proc_thread_self_init();
- proc_symlink("mounts", NULL, "self/mounts");
+ proc_symlink("mounts", NULL, "thread-self/mounts");
proc_net_init();
--
1.9.1
On Thu, 2014-07-31 at 17:30 -0700, Eric W. Biederman wrote:
> This is small chance changing /proc/net and /proc/mounts will cause
> userspace regressions (although nothing has shown up in my testing) if
> that happens we can just point the change that moves them from
> /proc/self/... to /proc/thread-self/...
Isn't breaking userspace a no no, no matter what? At least some
util-linux programs makes use of both /proc/mounts and /proc/net.