[PATCH] Fix invisible threads problem

When the main thread of a thread group has done pthread_exit() and died,
the other threads are still happily running, but will not be visible
under /proc because their leader is no longer accessible.

This fixes the access control so that we can see the sub-threads again.

Signed-off-by: Sripathi Kodi <sripathik@in.ibm.com>
Acked-by: Al Viro <viro@ftp.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 77 insertions, 7 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 23db452ab428..fb34f88a4a74 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -340,6 +340,52 @@ static int proc_root_link(struct inode *inode, struct dentry **dentry, struct vf
         return result;
 }
 
+
+/* Same as proc_root_link, but this addionally tries to get fs from other
+ * threads in the group */
+static int proc_task_root_link(struct inode *inode, struct dentry **dentry, struct vfsmount **mnt)
+{
+        struct fs_struct *fs;
+        int result = -ENOENT;
+        struct task_struct *leader = proc_task(inode);
+
+        task_lock(leader);
+        fs = leader->fs;
+        if (fs) {
+                atomic_inc(&fs->count);
+                task_unlock(leader);
+        } else {
+                /* Try to get fs from other threads */
+                task_unlock(leader);
+                struct task_struct *task = leader;
+                read_lock(&tasklist_lock);
+                if (pid_alive(task)) {
+                        while ((task = next_thread(task)) != leader) {
+                                task_lock(task);
+                                fs = task->fs;
+                                if (fs) {
+                                        atomic_inc(&fs->count);
+                                        task_unlock(task);
+                                        break;
+                                }
+                                task_unlock(task);
+                        }
+                }
+                read_unlock(&tasklist_lock);
+        }
+
+        if (fs) {
+                read_lock(&fs->lock);
+                *mnt = mntget(fs->rootmnt);
+                *dentry = dget(fs->root);
+                read_unlock(&fs->lock);
+                result = 0;
+                put_fs_struct(fs);
+        }
+        return result;
+}
+
+
 #define MAY_PTRACE(task) \
         (task == current || \
         (task->parent == current && \
@@ -471,14 +517,14 @@ static int proc_oom_score(struct task_struct *task, char *buffer)
 
 /* permission checks */
 
-static int proc_check_root(struct inode *inode)
+/* If the process being read is separated by chroot from the reading process,
+ * don't let the reader access the threads.
+ */
+static int proc_check_chroot(struct dentry *root, struct vfsmount *vfsmnt)
 {
-        struct dentry *de, *base, *root;
-        struct vfsmount *our_vfsmnt, *vfsmnt, *mnt;
+        struct dentry *de, *base;
+        struct vfsmount *our_vfsmnt, *mnt;
         int res = 0;
-
-        if (proc_root_link(inode, &root, &vfsmnt)) /* Ewww... */
-                return -ENOENT;
         read_lock(&current->fs->lock);
         our_vfsmnt = mntget(current->fs->rootmnt);
         base = dget(current->fs->root);
@@ -511,6 +557,16 @@ out:
         goto exit;
 }
 
+static int proc_check_root(struct inode *inode)
+{
+        struct dentry *root;
+        struct vfsmount *vfsmnt;
+
+        if (proc_root_link(inode, &root, &vfsmnt)) /* Ewww... */
+                return -ENOENT;
+        return proc_check_chroot(root, vfsmnt);
+}
+
 static int proc_permission(struct inode *inode, int mask, struct nameidata *nd)
 {
         if (generic_permission(inode, mask, NULL) != 0)
@@ -518,6 +574,20 @@ static int proc_permission(struct inode *inode, int mask, struct nameidata *nd)
         return proc_check_root(inode);
 }
 
+static int proc_task_permission(struct inode *inode, int mask, struct nameidata *nd)
+{
+        struct dentry *root;
+        struct vfsmount *vfsmnt;
+
+        if (generic_permission(inode, mask, NULL) != 0)
+                return -EACCES;
+
+        if (proc_task_root_link(inode, &root, &vfsmnt))
+                return -ENOENT;
+
+        return proc_check_chroot(root, vfsmnt);
+}
+
 extern struct seq_operations proc_pid_maps_op;
 static int maps_open(struct inode *inode, struct file *file)
 {
@@ -1419,7 +1489,7 @@ static struct inode_operations proc_fd_inode_operations = {
 
 static struct inode_operations proc_task_inode_operations = {
         .lookup         = proc_task_lookup,
-        .permission     = proc_permission,
+        .permission     = proc_task_permission,
 };
 
 #ifdef CONFIG_SECURITY