UPSTREAM: procfs: fixes pthread cross-thread naming if !PR_DUMPABLE

[firefly-linux-kernel-4.4.55.git] / fs / proc / base.c

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 23d60b1995fb29e89cf37c93464ca0274cb8cf59..2df808a810354be10a7d97f2abb71329226455fd 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3078,6 +3078,44 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
        return 0;
 }
 
+/*
+ * proc_tid_comm_permission is a special permission function exclusively
+ * used for the node /proc/<pid>/task/<tid>/comm.
+ * It bypasses generic permission checks in the case where a task of the same
+ * task group attempts to access the node.
+ * The rational behind this is that glibc and bionic access this node for
+ * cross thread naming (pthread_set/getname_np(!self)). However, if
+ * PR_SET_DUMPABLE gets set to 0 this node among others becomes uid=0 gid=0,
+ * which locks out the cross thread naming implementation.
+ * This function makes sure that the node is always accessible for members of
+ * same thread group.
+ */
+static int proc_tid_comm_permission(struct inode *inode, int mask)
+{
+       bool is_same_tgroup;
+       struct task_struct *task;
+
+       task = get_proc_task(inode);
+       if (!task)
+               return -ESRCH;
+       is_same_tgroup = same_thread_group(current, task);
+       put_task_struct(task);
+
+       if (likely(is_same_tgroup && !(mask & MAY_EXEC))) {
+               /* This file (/proc/<pid>/task/<tid>/comm) can always be
+                * read or written by the members of the corresponding
+                * thread group.
+                */
+               return 0;
+       }
+
+       return generic_permission(inode, mask);
+}
+
+static const struct inode_operations proc_tid_comm_inode_operations = {
+               .permission = proc_tid_comm_permission,
+};
+
 /*
  * Tasks
  */
@@ -3096,7 +3134,9 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_SCHED_DEBUG
        REG("sched",     S_IRUGO|S_IWUSR, proc_pid_sched_operations),
 #endif
-       REG("comm",      S_IRUGO|S_IWUSR, proc_pid_set_comm_operations),
+       NOD("comm",      S_IFREG|S_IRUGO|S_IWUSR,
+                        &proc_tid_comm_inode_operations,
+                        &proc_pid_set_comm_operations, {}),
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
        ONE("syscall",   S_IRUSR, proc_pid_syscall),
 #endif