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proc: don't (ab)use ->group_leader in proc_task_readdir() paths

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proc_task_readdir() does not really need "leader", first_tid() has to
revalidate it anyway.  Just pass proc_pid(inode) to first_tid() instead,
it can do pid_task(PIDTYPE_PID) itself and read ->group_leader only if
necessary.

The patch also extracts the "inode is dead" code from
pid_delete_dentry(dentry) into the new trivial helper,
proc_inode_is_dead(inode), proc_task_readdir() uses it to return -ENOENT
if this dir was removed.

This is a bit racy, but the race is very inlikely and the getdents() after
openndir() can see the empty "." + ".." dir only once.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Sameer Nanda <snanda@chromium.org>
Cc: Sergey Dyasly <dserrg@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:
Oleg Nesterov 2014-01-23 15:55:39 -08:00 committed by Linus Torvalds
parent c986c14a6a
commit d855a4b79f
1 changed files with 24 additions and 28 deletions
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52
fs/proc/base.c
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@ -1658,13 +1658,18 @@ int pid_revalidate(struct dentry *dentry, unsigned int flags)
return 0;
}
static inline bool proc_inode_is_dead(struct inode *inode)
{
return !proc_pid(inode)->tasks[PIDTYPE_PID].first;
}
int pid_delete_dentry(const struct dentry *dentry)
{
/* Is the task we represent dead?
* If so, then don't put the dentry on the lru list,
* kill it immediately.
*/
return !proc_pid(dentry->d_inode)->tasks[PIDTYPE_PID].first;
return proc_inode_is_dead(dentry->d_inode);
}
const struct dentry_operations pid_dentry_operations =
@ -3092,34 +3097,35 @@ out_no_task:
* In the case of a seek we start with the leader and walk nr
* threads past it.
*/
static struct task_struct *first_tid(struct task_struct *leader,
int tid, int nr, struct pid_namespace *ns)
static struct task_struct *first_tid(struct pid *pid, int tid,
int nr, struct pid_namespace *ns)
{
struct task_struct *pos;
struct task_struct *pos, *task;
rcu_read_lock();
/* Attempt to start with the pid of a thread */
task = pid_task(pid, PIDTYPE_PID);
if (!task)
goto fail;
/* Attempt to start with the tid of a thread */
if (tid && (nr > 0)) {
pos = find_task_by_pid_ns(tid, ns);
if (pos && (pos->group_leader == leader))
if (pos && same_thread_group(pos, task))
goto found;
}
/* If nr exceeds the number of threads there is nothing todo */
if (nr && nr >= get_nr_threads(leader))
goto fail;
/* It could be unhashed before we take rcu lock */
if (!pid_alive(leader))
if (nr && nr >= get_nr_threads(task))
goto fail;
/* If we haven't found our starting place yet start
* with the leader and walk nr threads forward.
*/
pos = leader;
pos = task = task->group_leader;
do {
if (nr-- <= 0)
goto found;
} while_each_thread(leader, pos);
} while_each_thread(task, pos);
fail:
pos = NULL;
goto out;
@ -3155,25 +3161,16 @@ static struct task_struct *next_tid(struct task_struct *start)
/* for the /proc/TGID/task/ directories */
static int proc_task_readdir(struct file *file, struct dir_context *ctx)
{
struct task_struct *leader = NULL;
struct task_struct *task = get_proc_task(file_inode(file));
struct inode *inode = file_inode(file);
struct task_struct *task;
struct pid_namespace *ns;
int tid;
if (!task)
return -ENOENT;
rcu_read_lock();
if (pid_alive(task)) {
leader = task->group_leader;
get_task_struct(leader);
}
rcu_read_unlock();
put_task_struct(task);
if (!leader)
if (proc_inode_is_dead(inode))
return -ENOENT;
if (!dir_emit_dots(file, ctx))
goto out;
return 0;
/* f_version caches the tgid value that the last readdir call couldn't
* return. lseek aka telldir automagically resets f_version to 0.
@ -3181,7 +3178,7 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
ns = file->f_dentry->d_sb->s_fs_info;
tid = (int)file->f_version;
file->f_version = 0;
for (task = first_tid(leader, tid, ctx->pos - 2, ns);
for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
task;
task = next_tid(task), ctx->pos++) {
char name[PROC_NUMBUF];
@ -3197,8 +3194,7 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
break;
}
}
out:
put_task_struct(leader);
return 0;
}