per signal_struct coredumps

Current coredumps are mixed up with the exit code, the signal handling
code and with the ptrace code in was they are much more complicated than
necessary and difficult to follow.

This series of changes starts with ptrace_stop and cleans it up,
making it easier to follow what is happening in ptrace_stop.
Then cleans up the exec interactions with coredumps.
Then cleans up the coredump interactions with exit.
Then the coredump interactions with the signal handling code is clean
up.

The first and last changes are bug fixes for minor bugs.

I believe the fact that vfork followed by execve can kill the process
the called vfork if exec fails is sufficient justification to change
the userspace visible behavior.

In previous conversations it was suggested that some of these cleanups
did not stand on their own.  I think I have managed to organize things
so all of their patches stand on their own.

Which means that if for some reason the last change needs to be reverted
we can still keep the gains from the other changes.

Eric W. Biederman (6):
      signal: Remove the bogus sigkill_pending in ptrace_stop
      ptrace: Remove the unnecessary arguments from arch_ptrace_stop
      exec: Check for a pending fatal signal instead of core_state
      exit: Factor coredump_exit_mm out of exit_mm
      coredump:  Don't perform any cleanups before dumping core
      coredump: Limit coredumps to a single thread group

 arch/ia64/include/asm/ptrace.h  |  4 +-
 arch/sparc/include/asm/ptrace.h |  8 ++--
 fs/binfmt_elf.c                 |  4 +-
 fs/binfmt_elf_fdpic.c           |  2 +-
 fs/coredump.c                   | 88 ++++++-----------------------------------
 fs/exec.c                       | 14 +++----
 fs/proc/array.c                 |  6 +--
 include/linux/mm_types.h        | 13 ------
 include/linux/ptrace.h          | 22 +++++------
 include/linux/sched.h           |  1 +
 include/linux/sched/signal.h    | 13 ++++++
 kernel/exit.c                   | 76 +++++++++++++++++++----------------
 kernel/fork.c                   |  4 +-
 kernel/signal.c                 | 49 ++++-------------------
 mm/debug.c                      |  4 +-
 mm/oom_kill.c                   |  6 +--
 16 files changed, 106 insertions(+), 208 deletions(-)

Link: https://lkml.kernel.org/r/87v92qx2c6.fsf@disp2133
Signed-off-by: "Eric W. Biederman" <[email protected]>

Author: ebiederm

arch/ia64/include/asm/ptrace.h

@@ -129,9 +129,9 @@ static inline long regs_return_value(struct pt_regs *regs)
   extern void ia64_decrement_ip (struct pt_regs *pt);
 
   extern void ia64_ptrace_stop(void);
-  #define arch_ptrace_stop(code, info) \
+  #define arch_ptrace_stop() \
 	ia64_ptrace_stop()
-  #define arch_ptrace_stop_needed(code, info) \
+  #define arch_ptrace_stop_needed() \
 	(!test_thread_flag(TIF_RESTORE_RSE))
 
   extern void ptrace_attach_sync_user_rbs (struct task_struct *);

arch/sparc/include/asm/ptrace.h

@@ -26,12 +26,12 @@ static inline bool pt_regs_clear_syscall(struct pt_regs *regs)
 	return (regs->tstate &= ~TSTATE_SYSCALL);
 }
 
-#define arch_ptrace_stop_needed(exit_code, info) \
+#define arch_ptrace_stop_needed() \
 ({	flush_user_windows(); \
 	get_thread_wsaved() != 0; \
 })
 
-#define arch_ptrace_stop(exit_code, info) \
+#define arch_ptrace_stop() \
 	synchronize_user_stack()
 
 #define current_pt_regs() \
@@ -129,12 +129,12 @@ static inline bool pt_regs_clear_syscall(struct pt_regs *regs)
 	return (regs->psr &= ~PSR_SYSCALL);
 }
 
-#define arch_ptrace_stop_needed(exit_code, info) \
+#define arch_ptrace_stop_needed() \
 ({	flush_user_windows(); \
 	current_thread_info()->w_saved != 0;	\
 })
 
-#define arch_ptrace_stop(exit_code, info) \
+#define arch_ptrace_stop() \
 	synchronize_user_stack()
 
 #define current_pt_regs() \

fs/binfmt_elf.c

@@ -1834,7 +1834,7 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
 	/*
 	 * Allocate a structure for each thread.
 	 */
-	for (ct = &dump_task->mm->core_state->dumper; ct; ct = ct->next) {
+	for (ct = &dump_task->signal->core_state->dumper; ct; ct = ct->next) {
 		t = kzalloc(offsetof(struct elf_thread_core_info,
 				     notes[info->thread_notes]),
 			    GFP_KERNEL);
@@ -2024,7 +2024,7 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
 	if (!elf_note_info_init(info))
 		return 0;
 
-	for (ct = current->mm->core_state->dumper.next;
+	for (ct = current->signal->core_state->dumper.next;
 					ct; ct = ct->next) {
 		ets = kzalloc(sizeof(*ets), GFP_KERNEL);
 		if (!ets)

fs/binfmt_elf_fdpic.c

@@ -1494,7 +1494,7 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
 	if (dump_vma_snapshot(cprm, &vma_count, &vma_meta, &vma_data_size))
 		goto end_coredump;
 
-	for (ct = current->mm->core_state->dumper.next;
+	for (ct = current->signal->core_state->dumper.next;
 					ct; ct = ct->next) {
 		tmp = elf_dump_thread_status(cprm->siginfo->si_signo,
 					     ct->task, &thread_status_size);

fs/coredump.c

@@ -359,7 +359,7 @@ static int zap_process(struct task_struct *start, int exit_code, int flags)
 
 	for_each_thread(start, t) {
 		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
-		if (t != current && t->mm) {
+		if (t != current && !(t->flags & PF_POSTCOREDUMP)) {
 			sigaddset(&t->pending.signal, SIGKILL);
 			signal_wake_up(t, 1);
 			nr++;
@@ -369,99 +369,34 @@ static int zap_process(struct task_struct *start, int exit_code, int flags)
 	return nr;
 }
 
-static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
+static int zap_threads(struct task_struct *tsk,
 			struct core_state *core_state, int exit_code)
 {
-	struct task_struct *g, *p;
-	unsigned long flags;
 	int nr = -EAGAIN;
 
 	spin_lock_irq(&tsk->sighand->siglock);
 	if (!signal_group_exit(tsk->signal)) {
-		mm->core_state = core_state;
+		tsk->signal->core_state = core_state;
 		tsk->signal->group_exit_task = tsk;
 		nr = zap_process(tsk, exit_code, 0);
 		clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
+		tsk->flags |= PF_DUMPCORE;
+		atomic_set(&core_state->nr_threads, nr);
 	}
 	spin_unlock_irq(&tsk->sighand->siglock);
-	if (unlikely(nr < 0))
-		return nr;
-
-	tsk->flags |= PF_DUMPCORE;
-	if (atomic_read(&mm->mm_users) == nr + 1)
-		goto done;
-	/*
-	 * We should find and kill all tasks which use this mm, and we should
-	 * count them correctly into ->nr_threads. We don't take tasklist
-	 * lock, but this is safe wrt:
-	 *
-	 * fork:
-	 *	None of sub-threads can fork after zap_process(leader). All
-	 *	processes which were created before this point should be
-	 *	visible to zap_threads() because copy_process() adds the new
-	 *	process to the tail of init_task.tasks list, and lock/unlock
-	 *	of ->siglock provides a memory barrier.
-	 *
-	 * do_exit:
-	 *	The caller holds mm->mmap_lock. This means that the task which
-	 *	uses this mm can't pass exit_mm(), so it can't exit or clear
-	 *	its ->mm.
-	 *
-	 * de_thread:
-	 *	It does list_replace_rcu(&leader->tasks, &current->tasks),
-	 *	we must see either old or new leader, this does not matter.
-	 *	However, it can change p->sighand, so lock_task_sighand(p)
-	 *	must be used. Since p->mm != NULL and we hold ->mmap_lock
-	 *	it can't fail.
-	 *
-	 *	Note also that "g" can be the old leader with ->mm == NULL
-	 *	and already unhashed and thus removed from ->thread_group.
-	 *	This is OK, __unhash_process()->list_del_rcu() does not
-	 *	clear the ->next pointer, we will find the new leader via
-	 *	next_thread().
-	 */
-	rcu_read_lock();
-	for_each_process(g) {
-		if (g == tsk->group_leader)
-			continue;
-		if (g->flags & PF_KTHREAD)
-			continue;
-
-		for_each_thread(g, p) {
-			if (unlikely(!p->mm))
-				continue;
-			if (unlikely(p->mm == mm)) {
-				lock_task_sighand(p, &flags);
-				nr += zap_process(p, exit_code,
-							SIGNAL_GROUP_EXIT);
-				unlock_task_sighand(p, &flags);
-			}
-			break;
-		}
-	}
-	rcu_read_unlock();
-done:
-	atomic_set(&core_state->nr_threads, nr);
 	return nr;
 }
 
 static int coredump_wait(int exit_code, struct core_state *core_state)
 {
 	struct task_struct *tsk = current;
-	struct mm_struct *mm = tsk->mm;
 	int core_waiters = -EBUSY;
 
 	init_completion(&core_state->startup);
 	core_state->dumper.task = tsk;
 	core_state->dumper.next = NULL;
 
-	if (mmap_write_lock_killable(mm))
-		return -EINTR;
-
-	if (!mm->core_state)
-		core_waiters = zap_threads(tsk, mm, core_state, exit_code);
-	mmap_write_unlock(mm);
-
+	core_waiters = zap_threads(tsk, core_state, exit_code);
 	if (core_waiters > 0) {
 		struct core_thread *ptr;
 
@@ -483,7 +418,7 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
 	return core_waiters;
 }
 
-static void coredump_finish(struct mm_struct *mm, bool core_dumped)
+static void coredump_finish(bool core_dumped)
 {
 	struct core_thread *curr, *next;
 	struct task_struct *task;
@@ -493,22 +428,21 @@ static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 		current->signal->group_exit_code |= 0x80;
 	current->signal->group_exit_task = NULL;
 	current->signal->flags = SIGNAL_GROUP_EXIT;
+	next = current->signal->core_state->dumper.next;
+	current->signal->core_state = NULL;
 	spin_unlock_irq(&current->sighand->siglock);
 
-	next = mm->core_state->dumper.next;
 	while ((curr = next) != NULL) {
 		next = curr->next;
 		task = curr->task;
 		/*
-		 * see exit_mm(), curr->task must not see
+		 * see coredump_task_exit(), curr->task must not see
 		 * ->task == NULL before we read ->next.
 		 */
 		smp_mb();
 		curr->task = NULL;
 		wake_up_process(task);
 	}
-
-	mm->core_state = NULL;
 }
 
 static bool dump_interrupted(void)
@@ -839,7 +773,7 @@ void do_coredump(const kernel_siginfo_t *siginfo)
 fail_unlock:
 	kfree(argv);
 	kfree(cn.corename);
-	coredump_finish(mm, core_dumped);
+	coredump_finish(core_dumped);
 	revert_creds(old_cred);
 fail_creds:
 	put_cred(cred);

fs/exec.c

@@ -987,16 +987,14 @@ static int exec_mmap(struct mm_struct *mm)
 
 	if (old_mm) {
 		/*
-		 * Make sure that if there is a core dump in progress
-		 * for the old mm, we get out and die instead of going
-		 * through with the exec.  We must hold mmap_lock around
-		 * checking core_state and changing tsk->mm.
+		 * If there is a pending fatal signal perhaps a signal
+		 * whose default action is to create a coredump get
+		 * out and die instead of going through with the exec.
 		 */
-		mmap_read_lock(old_mm);
-		if (unlikely(old_mm->core_state)) {
-			mmap_read_unlock(old_mm);
+		ret = mmap_read_lock_killable(old_mm);
+		if (ret) {
 			up_write(&tsk->signal->exec_update_lock);
-			return -EINTR;
+			return ret;
 		}
 	}
 

fs/proc/array.c

@@ -408,9 +408,9 @@ static void task_cpus_allowed(struct seq_file *m, struct task_struct *task)
 		   cpumask_pr_args(&task->cpus_mask));
 }
 
-static inline void task_core_dumping(struct seq_file *m, struct mm_struct *mm)
+static inline void task_core_dumping(struct seq_file *m, struct task_struct *task)
 {
-	seq_put_decimal_ull(m, "CoreDumping:\t", !!mm->core_state);
+	seq_put_decimal_ull(m, "CoreDumping:\t", !!task->signal->core_state);
 	seq_putc(m, '\n');
 }
 
@@ -436,7 +436,7 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
 
 	if (mm) {
 		task_mem(m, mm);
-		task_core_dumping(m, mm);
+		task_core_dumping(m, task);
 		task_thp_status(m, mm);
 		mmput(mm);
 	}

include/linux/mm_types.h

@@ -387,17 +387,6 @@ struct vm_area_struct {
 	struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
 } __randomize_layout;
 
-struct core_thread {
-	struct task_struct *task;
-	struct core_thread *next;
-};
-
-struct core_state {
-	atomic_t nr_threads;
-	struct core_thread dumper;
-	struct completion startup;
-};
-
 struct kioctx_table;
 struct mm_struct {
 	struct {
@@ -518,8 +507,6 @@ struct mm_struct {
 
 		unsigned long flags; /* Must use atomic bitops to access */
 
-		struct core_state *core_state; /* coredumping support */
-
 #ifdef CONFIG_AIO
 		spinlock_t			ioctx_lock;
 		struct kioctx_table __rcu	*ioctx_table;

include/linux/ptrace.h

@@ -362,29 +362,25 @@ static inline void user_single_step_report(struct pt_regs *regs)
 #ifndef arch_ptrace_stop_needed
 /**
  * arch_ptrace_stop_needed - Decide whether arch_ptrace_stop() should be called
- * @code:	current->exit_code value ptrace will stop with
- * @info:	siginfo_t pointer (or %NULL) for signal ptrace will stop with
  *
  * This is called with the siglock held, to decide whether or not it's
- * necessary to release the siglock and call arch_ptrace_stop() with the
- * same @code and @info arguments.  It can be defined to a constant if
- * arch_ptrace_stop() is never required, or always is.  On machines where
- * this makes sense, it should be defined to a quick test to optimize out
- * calling arch_ptrace_stop() when it would be superfluous.  For example,
- * if the thread has not been back to user mode since the last stop, the
- * thread state might indicate that nothing needs to be done.
+ * necessary to release the siglock and call arch_ptrace_stop().  It can be
+ * defined to a constant if arch_ptrace_stop() is never required, or always
+ * is.  On machines where this makes sense, it should be defined to a quick
+ * test to optimize out calling arch_ptrace_stop() when it would be
+ * superfluous.  For example, if the thread has not been back to user mode
+ * since the last stop, the thread state might indicate that nothing needs
+ * to be done.
  *
  * This is guaranteed to be invoked once before a task stops for ptrace and
  * may include arch-specific operations necessary prior to a ptrace stop.
  */
-#define arch_ptrace_stop_needed(code, info)	(0)
+#define arch_ptrace_stop_needed()	(0)
 #endif
 
 #ifndef arch_ptrace_stop
 /**
  * arch_ptrace_stop - Do machine-specific work before stopping for ptrace
- * @code:	current->exit_code value ptrace will stop with
- * @info:	siginfo_t pointer (or %NULL) for signal ptrace will stop with
  *
  * This is called with no locks held when arch_ptrace_stop_needed() has
  * just returned nonzero.  It is allowed to block, e.g. for user memory
@@ -394,7 +390,7 @@ static inline void user_single_step_report(struct pt_regs *regs)
  * we only do it when the arch requires it for this particular stop, as
  * indicated by arch_ptrace_stop_needed().
  */
-#define arch_ptrace_stop(code, info)		do { } while (0)
+#define arch_ptrace_stop()		do { } while (0)
 #endif
 
 #ifndef current_pt_regs

include/linux/sched.h

@@ -1664,6 +1664,7 @@ extern struct pid *cad_pid;
 #define PF_VCPU			0x00000001	/* I'm a virtual CPU */
 #define PF_IDLE			0x00000002	/* I am an IDLE thread */
 #define PF_EXITING		0x00000004	/* Getting shut down */
+#define PF_POSTCOREDUMP		0x00000008	/* Coredumps should ignore this task */
 #define PF_IO_WORKER		0x00000010	/* Task is an IO worker */
 #define PF_WQ_WORKER		0x00000020	/* I'm a workqueue worker */
 #define PF_FORKNOEXEC		0x00000040	/* Forked but didn't exec */