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proc: remove races from proc_id_readdir() 

Oleg noticed that the call of task_pid_nr_ns() in proc_pid_readdir
is racy with respect to tasks exiting.

After a bit of examination it also appears that the call itself
is completely unnecessary.

So to fix the problem this patch modifies next_tgid() to return
both a tgid and the task struct in question.

A structure is introduced to return these values because it is
slightly cleaner and easier to optimize, and the resulting code
is a little shorter.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric W. Biederman 2007-11-28 16:21:26 -08:00 committed by Linus Torvalds
parent c895078355
commit 19fd4bb2a0
1 changed files with 28 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

51
fs/proc/base.c
View File

@ -2411,19 +2411,23 @@ out:
* Find the first task with tgid >= tgid
*
*/
static struct task_struct *next_tgid(unsigned int tgid,
struct pid_namespace *ns)
{
struct tgid_iter {
unsigned int tgid;
struct task_struct *task;
};
static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter iter)
{
struct pid *pid;
if (iter.task)
put_task_struct(iter.task);
rcu_read_lock();
retry:
task = NULL;
pid = find_ge_pid(tgid, ns);
iter.task = NULL;
pid = find_ge_pid(iter.tgid, ns);
if (pid) {
tgid = pid_nr_ns(pid, ns) + 1;
task = pid_task(pid, PIDTYPE_PID);
iter.tgid = pid_nr_ns(pid, ns);
iter.task = pid_task(pid, PIDTYPE_PID);
/* What we to know is if the pid we have find is the
* pid of a thread_group_leader. Testing for task
* being a thread_group_leader is the obvious thing
@ -2436,23 +2440,25 @@ retry:
* found doesn't happen to be a thread group leader.
* As we don't care in the case of readdir.
*/
if (!task || !has_group_leader_pid(task))
if (!iter.task || !has_group_leader_pid(iter.task)) {
iter.tgid += 1;
goto retry;
get_task_struct(task);
}
get_task_struct(iter.task);
}
rcu_read_unlock();
return task;
return iter;
}
#define TGID_OFFSET (FIRST_PROCESS_ENTRY + ARRAY_SIZE(proc_base_stuff))
static int proc_pid_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
struct task_struct *task, int tgid)
struct tgid_iter iter)
{
char name[PROC_NUMBUF];
int len = snprintf(name, sizeof(name), "%d", tgid);
int len = snprintf(name, sizeof(name), "%d", iter.tgid);
return proc_fill_cache(filp, dirent, filldir, name, len,
proc_pid_instantiate, task, NULL);
proc_pid_instantiate, iter.task, NULL);
}
/* for the /proc/ directory itself, after non-process stuff has been done */
@ -2460,8 +2466,7 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
unsigned int nr = filp->f_pos - FIRST_PROCESS_ENTRY;
struct task_struct *reaper = get_proc_task(filp->f_path.dentry->d_inode);
struct task_struct *task;
int tgid;
struct tgid_iter iter;
struct pid_namespace *ns;
if (!reaper)
@ -2474,14 +2479,14 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
}
ns = filp->f_dentry->d_sb->s_fs_info;
tgid = filp->f_pos - TGID_OFFSET;
for (task = next_tgid(tgid, ns);
task;
put_task_struct(task), task = next_tgid(tgid + 1, ns)) {
tgid = task_pid_nr_ns(task, ns);
filp->f_pos = tgid + TGID_OFFSET;
if (proc_pid_fill_cache(filp, dirent, filldir, task, tgid) < 0) {
put_task_struct(task);
iter.task = NULL;
iter.tgid = filp->f_pos - TGID_OFFSET;
for (iter = next_tgid(ns, iter);
iter.task;
iter.tgid += 1, iter = next_tgid(ns, iter)) {
filp->f_pos = iter.tgid + TGID_OFFSET;
if (proc_pid_fill_cache(filp, dirent, filldir, iter) < 0) {
put_task_struct(iter.task);
goto out;
}
}