Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1169 insertions, 0 deletions

diff --git a/fs/coredump.c b/fs/coredump.c
new file mode 100644
index 000000000..9d91e831e
--- /dev/null
+++ b/fs/coredump.c
@@ -0,0 +1,1169 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/slab.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
+#include <linux/freezer.h>
+#include <linux/mm.h>
+#include <linux/stat.h>
+#include <linux/fcntl.h>
+#include <linux/swap.h>
+#include <linux/ctype.h>
+#include <linux/string.h>
+#include <linux/init.h>
+#include <linux/pagemap.h>
+#include <linux/perf_event.h>
+#include <linux/highmem.h>
+#include <linux/spinlock.h>
+#include <linux/key.h>
+#include <linux/personality.h>
+#include <linux/binfmts.h>
+#include <linux/coredump.h>
+#include <linux/sched/coredump.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/task_stack.h>
+#include <linux/utsname.h>
+#include <linux/pid_namespace.h>
+#include <linux/module.h>
+#include <linux/namei.h>
+#include <linux/mount.h>
+#include <linux/security.h>
+#include <linux/syscalls.h>
+#include <linux/tsacct_kern.h>
+#include <linux/cn_proc.h>
+#include <linux/audit.h>
+#include <linux/tracehook.h>
+#include <linux/kmod.h>
+#include <linux/fsnotify.h>
+#include <linux/fs_struct.h>
+#include <linux/pipe_fs_i.h>
+#include <linux/oom.h>
+#include <linux/compat.h>
+#include <linux/fs.h>
+#include <linux/path.h>
+#include <linux/timekeeping.h>
+#include <linux/elf.h>
+
+#include <linux/uaccess.h>
+#include <asm/mmu_context.h>
+#include <asm/tlb.h>
+#include <asm/exec.h>
+
+#include <trace/events/task.h>
+#include "internal.h"
+
+#include <trace/events/sched.h>
+
+static bool dump_vma_snapshot(struct coredump_params *cprm);
+static void free_vma_snapshot(struct coredump_params *cprm);
+
+int core_uses_pid;
+unsigned int core_pipe_limit;
+char core_pattern[CORENAME_MAX_SIZE] = "core";
+static int core_name_size = CORENAME_MAX_SIZE;
+
+struct core_name {
+	char *corename;
+	int used, size;
+};
+
+/* The maximal length of core_pattern is also specified in sysctl.c */
+
+static int expand_corename(struct core_name *cn, int size)
+{
+	char *corename = krealloc(cn->corename, size, GFP_KERNEL);
+
+	if (!corename)
+		return -ENOMEM;
+
+	if (size > core_name_size) /* racy but harmless */
+		core_name_size = size;
+
+	cn->size = ksize(corename);
+	cn->corename = corename;
+	return 0;
+}
+
+static __printf(2, 0) int cn_vprintf(struct core_name *cn, const char *fmt,
+				     va_list arg)
+{
+	int free, need;
+	va_list arg_copy;
+
+again:
+	free = cn->size - cn->used;
+
+	va_copy(arg_copy, arg);
+	need = vsnprintf(cn->corename + cn->used, free, fmt, arg_copy);
+	va_end(arg_copy);
+
+	if (need < free) {
+		cn->used += need;
+		return 0;
+	}
+
+	if (!expand_corename(cn, cn->size + need - free + 1))
+		goto again;
+
+	return -ENOMEM;
+}
+
+static __printf(2, 3) int cn_printf(struct core_name *cn, const char *fmt, ...)
+{
+	va_list arg;
+	int ret;
+
+	va_start(arg, fmt);
+	ret = cn_vprintf(cn, fmt, arg);
+	va_end(arg);
+
+	return ret;
+}
+
+static __printf(2, 3)
+int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
+{
+	int cur = cn->used;
+	va_list arg;
+	int ret;
+
+	va_start(arg, fmt);
+	ret = cn_vprintf(cn, fmt, arg);
+	va_end(arg);
+
+	if (ret == 0) {
+		/*
+		 * Ensure that this coredump name component can't cause the
+		 * resulting corefile path to consist of a ".." or ".".
+		 */
+		if ((cn->used - cur == 1 && cn->corename[cur] == '.') ||
+				(cn->used - cur == 2 && cn->corename[cur] == '.'
+				&& cn->corename[cur+1] == '.'))
+			cn->corename[cur] = '!';
+
+		/*
+		 * Empty names are fishy and could be used to create a "//" in a
+		 * corefile name, causing the coredump to happen one directory
+		 * level too high. Enforce that all components of the core
+		 * pattern are at least one character long.
+		 */
+		if (cn->used == cur)
+			ret = cn_printf(cn, "!");
+	}
+
+	for (; cur < cn->used; ++cur) {
+		if (cn->corename[cur] == '/')
+			cn->corename[cur] = '!';
+	}
+	return ret;
+}
+
+static int cn_print_exe_file(struct core_name *cn, bool name_only)
+{
+	struct file *exe_file;
+	char *pathbuf, *path, *ptr;
+	int ret;
+
+	exe_file = get_mm_exe_file(current->mm);
+	if (!exe_file)
+		return cn_esc_printf(cn, "%s (path unknown)", current->comm);
+
+	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!pathbuf) {
+		ret = -ENOMEM;
+		goto put_exe_file;
+	}
+
+	path = file_path(exe_file, pathbuf, PATH_MAX);
+	if (IS_ERR(path)) {
+		ret = PTR_ERR(path);
+		goto free_buf;
+	}
+
+	if (name_only) {
+		ptr = strrchr(path, '/');
+		if (ptr)
+			path = ptr + 1;
+	}
+	ret = cn_esc_printf(cn, "%s", path);
+
+free_buf:
+	kfree(pathbuf);
+put_exe_file:
+	fput(exe_file);
+	return ret;
+}
+
+/* format_corename will inspect the pattern parameter, and output a
+ * name into corename, which must have space for at least
+ * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
+ */
+static int format_corename(struct core_name *cn, struct coredump_params *cprm,
+			   size_t **argv, int *argc)
+{
+	const struct cred *cred = current_cred();
+	const char *pat_ptr = core_pattern;
+	int ispipe = (*pat_ptr == '|');
+	bool was_space = false;
+	int pid_in_pattern = 0;
+	int err = 0;
+
+	cn->used = 0;
+	cn->corename = NULL;
+	if (expand_corename(cn, core_name_size))
+		return -ENOMEM;
+	cn->corename[0] = '\0';
+
+	if (ispipe) {
+		int argvs = sizeof(core_pattern) / 2;
+		(*argv) = kmalloc_array(argvs, sizeof(**argv), GFP_KERNEL);
+		if (!(*argv))
+			return -ENOMEM;
+		(*argv)[(*argc)++] = 0;
+		++pat_ptr;
+		if (!(*pat_ptr))
+			return -ENOMEM;
+	}
+
+	/* Repeat as long as we have more pattern to process and more output
+	   space */
+	while (*pat_ptr) {
+		/*
+		 * Split on spaces before doing template expansion so that
+		 * %e and %E don't get split if they have spaces in them
+		 */
+		if (ispipe) {
+			if (isspace(*pat_ptr)) {
+				if (cn->used != 0)
+					was_space = true;
+				pat_ptr++;
+				continue;
+			} else if (was_space) {
+				was_space = false;
+				err = cn_printf(cn, "%c", '\0');
+				if (err)
+					return err;
+				(*argv)[(*argc)++] = cn->used;
+			}
+		}
+		if (*pat_ptr != '%') {
+			err = cn_printf(cn, "%c", *pat_ptr++);
+		} else {
+			switch (*++pat_ptr) {
+			/* single % at the end, drop that */
+			case 0:
+				goto out;
+			/* Double percent, output one percent */
+			case '%':
+				err = cn_printf(cn, "%c", '%');
+				break;
+			/* pid */
+			case 'p':
+				pid_in_pattern = 1;
+				err = cn_printf(cn, "%d",
+					      task_tgid_vnr(current));
+				break;
+			/* global pid */
+			case 'P':
+				err = cn_printf(cn, "%d",
+					      task_tgid_nr(current));
+				break;
+			case 'i':
+				err = cn_printf(cn, "%d",
+					      task_pid_vnr(current));
+				break;
+			case 'I':
+				err = cn_printf(cn, "%d",
+					      task_pid_nr(current));
+				break;
+			/* uid */
+			case 'u':
+				err = cn_printf(cn, "%u",
+						from_kuid(&init_user_ns,
+							  cred->uid));
+				break;
+			/* gid */
+			case 'g':
+				err = cn_printf(cn, "%u",
+						from_kgid(&init_user_ns,
+							  cred->gid));
+				break;
+			case 'd':
+				err = cn_printf(cn, "%d",
+					__get_dumpable(cprm->mm_flags));
+				break;
+			/* signal that caused the coredump */
+			case 's':
+				err = cn_printf(cn, "%d",
+						cprm->siginfo->si_signo);
+				break;
+			/* UNIX time of coredump */
+			case 't': {
+				time64_t time;
+
+				time = ktime_get_real_seconds();
+				err = cn_printf(cn, "%lld", time);
+				break;
+			}
+			/* hostname */
+			case 'h':
+				down_read(&uts_sem);
+				err = cn_esc_printf(cn, "%s",
+					      utsname()->nodename);
+				up_read(&uts_sem);
+				break;
+			/* executable, could be changed by prctl PR_SET_NAME etc */
+			case 'e':
+				err = cn_esc_printf(cn, "%s", current->comm);
+				break;
+			/* file name of executable */
+			case 'f':
+				err = cn_print_exe_file(cn, true);
+				break;
+			case 'E':
+				err = cn_print_exe_file(cn, false);
+				break;
+			/* core limit size */
+			case 'c':
+				err = cn_printf(cn, "%lu",
+					      rlimit(RLIMIT_CORE));
+				break;
+			default:
+				break;
+			}
+			++pat_ptr;
+		}
+
+		if (err)
+			return err;
+	}
+
+out:
+	/* Backward compatibility with core_uses_pid:
+	 *
+	 * If core_pattern does not include a %p (as is the default)
+	 * and core_uses_pid is set, then .%pid will be appended to
+	 * the filename. Do not do this for piped commands. */
+	if (!ispipe && !pid_in_pattern && core_uses_pid) {
+		err = cn_printf(cn, ".%d", task_tgid_vnr(current));
+		if (err)
+			return err;
+	}
+	return ispipe;
+}
+
+static int zap_process(struct task_struct *start, int exit_code, int flags)
+{
+	struct task_struct *t;
+	int nr = 0;
+
+	/* ignore all signals except SIGKILL, see prepare_signal() */
+	start->signal->flags = SIGNAL_GROUP_COREDUMP | flags;
+	start->signal->group_exit_code = exit_code;
+	start->signal->group_stop_count = 0;
+
+	for_each_thread(start, t) {
+		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
+		if (t != current && t->mm) {
+			sigaddset(&t->pending.signal, SIGKILL);
+			signal_wake_up(t, 1);
+			nr++;
+		}
+	}
+
+	return nr;
+}
+
+static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
+			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->group_exit_task = tsk;
+		nr = zap_process(tsk, exit_code, 0);
+		clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
+	}
+	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);
+
+	if (core_waiters > 0) {
+		struct core_thread *ptr;
+
+		freezer_do_not_count();
+		wait_for_completion(&core_state->startup);
+		freezer_count();
+		/*
+		 * Wait for all the threads to become inactive, so that
+		 * all the thread context (extended register state, like
+		 * fpu etc) gets copied to the memory.
+		 */
+		ptr = core_state->dumper.next;
+		while (ptr != NULL) {
+			wait_task_inactive(ptr->task, 0);
+			ptr = ptr->next;
+		}
+	}
+
+	return core_waiters;
+}
+
+static void coredump_finish(struct mm_struct *mm, bool core_dumped)
+{
+	struct core_thread *curr, *next;
+	struct task_struct *task;
+
+	spin_lock_irq(&current->sighand->siglock);
+	if (core_dumped && !__fatal_signal_pending(current))
+		current->signal->group_exit_code |= 0x80;
+	current->signal->group_exit_task = NULL;
+	current->signal->flags = SIGNAL_GROUP_EXIT;
+	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
+		 * ->task == NULL before we read ->next.
+		 */
+		smp_mb();
+		curr->task = NULL;
+		wake_up_process(task);
+	}
+
+	mm->core_state = NULL;
+}
+
+static bool dump_interrupted(void)
+{
+	/*
+	 * SIGKILL or freezing() interrupt the coredumping. Perhaps we
+	 * can do try_to_freeze() and check __fatal_signal_pending(),
+	 * but then we need to teach dump_write() to restart and clear
+	 * TIF_SIGPENDING.
+	 */
+	return fatal_signal_pending(current) || freezing(current);
+}
+
+static void wait_for_dump_helpers(struct file *file)
+{
+	struct pipe_inode_info *pipe = file->private_data;
+
+	pipe_lock(pipe);
+	pipe->readers++;
+	pipe->writers--;
+	wake_up_interruptible_sync(&pipe->rd_wait);
+	kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
+	pipe_unlock(pipe);
+
+	/*
+	 * We actually want wait_event_freezable() but then we need
+	 * to clear TIF_SIGPENDING and improve dump_interrupted().
+	 */
+	wait_event_interruptible(pipe->rd_wait, pipe->readers == 1);
+
+	pipe_lock(pipe);
+	pipe->readers--;
+	pipe->writers++;
+	pipe_unlock(pipe);
+}
+
+/*
+ * umh_pipe_setup
+ * helper function to customize the process used
+ * to collect the core in userspace.  Specifically
+ * it sets up a pipe and installs it as fd 0 (stdin)
+ * for the process.  Returns 0 on success, or
+ * PTR_ERR on failure.
+ * Note that it also sets the core limit to 1.  This
+ * is a special value that we use to trap recursive
+ * core dumps
+ */
+static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
+{
+	struct file *files[2];
+	struct coredump_params *cp = (struct coredump_params *)info->data;
+	int err = create_pipe_files(files, 0);
+	if (err)
+		return err;
+
+	cp->file = files[1];
+
+	err = replace_fd(0, files[0], 0);
+	fput(files[0]);
+	/* and disallow core files too */
+	current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
+
+	return err;
+}
+
+void do_coredump(const kernel_siginfo_t *siginfo)
+{
+	struct core_state core_state;
+	struct core_name cn;
+	struct mm_struct *mm = current->mm;
+	struct linux_binfmt * binfmt;
+	const struct cred *old_cred;
+	struct cred *cred;
+	int retval = 0;
+	int ispipe;
+	size_t *argv = NULL;
+	int argc = 0;
+	struct files_struct *displaced;
+	/* require nonrelative corefile path and be extra careful */
+	bool need_suid_safe = false;
+	bool core_dumped = false;
+	static atomic_t core_dump_count = ATOMIC_INIT(0);
+	struct coredump_params cprm = {
+		.siginfo = siginfo,
+		.regs = signal_pt_regs(),
+		.limit = rlimit(RLIMIT_CORE),
+		/*
+		 * We must use the same mm->flags while dumping core to avoid
+		 * inconsistency of bit flags, since this flag is not protected
+		 * by any locks.
+		 */
+		.mm_flags = mm->flags,
+		.vma_meta = NULL,
+	};
+
+	audit_core_dumps(siginfo->si_signo);
+
+	binfmt = mm->binfmt;
+	if (!binfmt || !binfmt->core_dump)
+		goto fail;
+	if (!__get_dumpable(cprm.mm_flags))
+		goto fail;
+
+	cred = prepare_creds();
+	if (!cred)
+		goto fail;
+	/*
+	 * We cannot trust fsuid as being the "true" uid of the process
+	 * nor do we know its entire history. We only know it was tainted
+	 * so we dump it as root in mode 2, and only into a controlled
+	 * environment (pipe handler or fully qualified path).
+	 */
+	if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
+		/* Setuid core dump mode */
+		cred->fsuid = GLOBAL_ROOT_UID;	/* Dump root private */
+		need_suid_safe = true;
+	}
+
+	retval = coredump_wait(siginfo->si_signo, &core_state);
+	if (retval < 0)
+		goto fail_creds;
+
+	old_cred = override_creds(cred);
+
+	ispipe = format_corename(&cn, &cprm, &argv, &argc);
+
+	if (ispipe) {
+		int argi;
+		int dump_count;
+		char **helper_argv;
+		struct subprocess_info *sub_info;
+
+		if (ispipe < 0) {
+			printk(KERN_WARNING "format_corename failed\n");
+			printk(KERN_WARNING "Aborting core\n");
+			goto fail_unlock;
+		}
+
+		if (cprm.limit == 1) {
+			/* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
+			 *
+			 * Normally core limits are irrelevant to pipes, since
+			 * we're not writing to the file system, but we use
+			 * cprm.limit of 1 here as a special value, this is a
+			 * consistent way to catch recursive crashes.
+			 * We can still crash if the core_pattern binary sets
+			 * RLIM_CORE = !1, but it runs as root, and can do
+			 * lots of stupid things.
+			 *
+			 * Note that we use task_tgid_vnr here to grab the pid
+			 * of the process group leader.  That way we get the
+			 * right pid if a thread in a multi-threaded
+			 * core_pattern process dies.
+			 */
+			printk(KERN_WARNING
+				"Process %d(%s) has RLIMIT_CORE set to 1\n",
+				task_tgid_vnr(current), current->comm);
+			printk(KERN_WARNING "Aborting core\n");
+			goto fail_unlock;
+		}
+		cprm.limit = RLIM_INFINITY;
+
+		dump_count = atomic_inc_return(&core_dump_count);
+		if (core_pipe_limit && (core_pipe_limit < dump_count)) {
+			printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
+			       task_tgid_vnr(current), current->comm);
+			printk(KERN_WARNING "Skipping core dump\n");
+			goto fail_dropcount;
+		}
+
+		helper_argv = kmalloc_array(argc + 1, sizeof(*helper_argv),
+					    GFP_KERNEL);
+		if (!helper_argv) {
+			printk(KERN_WARNING "%s failed to allocate memory\n",
+			       __func__);
+			goto fail_dropcount;
+		}
+		for (argi = 0; argi < argc; argi++)
+			helper_argv[argi] = cn.corename + argv[argi];
+		helper_argv[argi] = NULL;
+
+		retval = -ENOMEM;
+		sub_info = call_usermodehelper_setup(helper_argv[0],
+						helper_argv, NULL, GFP_KERNEL,
+						umh_pipe_setup, NULL, &cprm);
+		if (sub_info)
+			retval = call_usermodehelper_exec(sub_info,
+							  UMH_WAIT_EXEC);
+
+		kfree(helper_argv);
+		if (retval) {
+			printk(KERN_INFO "Core dump to |%s pipe failed\n",
+			       cn.corename);
+			goto close_fail;
+		}
+	} else {
+		struct inode *inode;
+		int open_flags = O_CREAT | O_RDWR | O_NOFOLLOW |
+				 O_LARGEFILE | O_EXCL;
+
+		if (cprm.limit < binfmt->min_coredump)
+			goto fail_unlock;
+
+		if (need_suid_safe && cn.corename[0] != '/') {
+			printk(KERN_WARNING "Pid %d(%s) can only dump core "\
+				"to fully qualified path!\n",
+				task_tgid_vnr(current), current->comm);
+			printk(KERN_WARNING "Skipping core dump\n");
+			goto fail_unlock;
+		}
+
+		/*
+		 * Unlink the file if it exists unless this is a SUID
+		 * binary - in that case, we're running around with root
+		 * privs and don't want to unlink another user's coredump.
+		 */
+		if (!need_suid_safe) {
+			/*
+			 * If it doesn't exist, that's fine. If there's some
+			 * other problem, we'll catch it at the filp_open().
+			 */
+			do_unlinkat(AT_FDCWD, getname_kernel(cn.corename));
+		}
+
+		/*
+		 * There is a race between unlinking and creating the
+		 * file, but if that causes an EEXIST here, that's
+		 * fine - another process raced with us while creating
+		 * the corefile, and the other process won. To userspace,
+		 * what matters is that at least one of the two processes
+		 * writes its coredump successfully, not which one.
+		 */
+		if (need_suid_safe) {
+			/*
+			 * Using user namespaces, normal user tasks can change
+			 * their current->fs->root to point to arbitrary
+			 * directories. Since the intention of the "only dump
+			 * with a fully qualified path" rule is to control where
+			 * coredumps may be placed using root privileges,
+			 * current->fs->root must not be used. Instead, use the
+			 * root directory of init_task.
+			 */
+			struct path root;
+
+			task_lock(&init_task);
+			get_fs_root(init_task.fs, &root);
+			task_unlock(&init_task);
+			cprm.file = file_open_root(root.dentry, root.mnt,
+				cn.corename, open_flags, 0600);
+			path_put(&root);
+		} else {
+			cprm.file = filp_open(cn.corename, open_flags, 0600);
+		}
+		if (IS_ERR(cprm.file))
+			goto fail_unlock;
+
+		inode = file_inode(cprm.file);
+		if (inode->i_nlink > 1)
+			goto close_fail;
+		if (d_unhashed(cprm.file->f_path.dentry))
+			goto close_fail;
+		/*
+		 * AK: actually i see no reason to not allow this for named
+		 * pipes etc, but keep the previous behaviour for now.
+		 */
+		if (!S_ISREG(inode->i_mode))
+			goto close_fail;
+		/*
+		 * Don't dump core if the filesystem changed owner or mode
+		 * of the file during file creation. This is an issue when
+		 * a process dumps core while its cwd is e.g. on a vfat
+		 * filesystem.
+		 */
+		if (!uid_eq(inode->i_uid, current_fsuid()))
+			goto close_fail;
+		if ((inode->i_mode & 0677) != 0600)
+			goto close_fail;
+		if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
+			goto close_fail;
+		if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
+			goto close_fail;
+	}
+
+	/* get us an unshared descriptor table; almost always a no-op */
+	retval = unshare_files(&displaced);
+	if (retval)
+		goto close_fail;
+	if (displaced)
+		put_files_struct(displaced);
+	if (!dump_interrupted()) {
+		/*
+		 * umh disabled with CONFIG_STATIC_USERMODEHELPER_PATH="" would
+		 * have this set to NULL.
+		 */
+		if (!cprm.file) {
+			pr_info("Core dump to |%s disabled\n", cn.corename);
+			goto close_fail;
+		}
+		if (!dump_vma_snapshot(&cprm))
+			goto close_fail;
+
+		file_start_write(cprm.file);
+		core_dumped = binfmt->core_dump(&cprm);
+		file_end_write(cprm.file);
+		free_vma_snapshot(&cprm);
+	}
+	if (ispipe && core_pipe_limit)
+		wait_for_dump_helpers(cprm.file);
+close_fail:
+	if (cprm.file)
+		filp_close(cprm.file, NULL);
+fail_dropcount:
+	if (ispipe)
+		atomic_dec(&core_dump_count);
+fail_unlock:
+	kfree(argv);
+	kfree(cn.corename);
+	coredump_finish(mm, core_dumped);
+	revert_creds(old_cred);
+fail_creds:
+	put_cred(cred);
+fail:
+	return;
+}
+
+/*
+ * Core dumping helper functions.  These are the only things you should
+ * do on a core-file: use only these functions to write out all the
+ * necessary info.
+ */
+int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
+{
+	struct file *file = cprm->file;
+	loff_t pos = file->f_pos;
+	ssize_t n;
+	if (cprm->written + nr > cprm->limit)
+		return 0;
+
+
+	if (dump_interrupted())
+		return 0;
+	n = __kernel_write(file, addr, nr, &pos);
+	if (n != nr)
+		return 0;
+	file->f_pos = pos;
+	cprm->written += n;
+	cprm->pos += n;
+
+	return 1;
+}
+EXPORT_SYMBOL(dump_emit);
+
+int dump_skip(struct coredump_params *cprm, size_t nr)
+{
+	static char zeroes[PAGE_SIZE];
+	struct file *file = cprm->file;
+	if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
+		if (dump_interrupted() ||
+		    file->f_op->llseek(file, nr, SEEK_CUR) < 0)
+			return 0;
+		cprm->pos += nr;
+		return 1;
+	} else {
+		while (nr > PAGE_SIZE) {
+			if (!dump_emit(cprm, zeroes, PAGE_SIZE))
+				return 0;
+			nr -= PAGE_SIZE;
+		}
+		return dump_emit(cprm, zeroes, nr);
+	}
+}
+EXPORT_SYMBOL(dump_skip);
+
+#ifdef CONFIG_ELF_CORE
+int dump_user_range(struct coredump_params *cprm, unsigned long start,
+		    unsigned long len)
+{
+	unsigned long addr;
+
+	for (addr = start; addr < start + len; addr += PAGE_SIZE) {
+		struct page *page;
+		int stop;
+
+		/*
+		 * To avoid having to allocate page tables for virtual address
+		 * ranges that have never been used yet, and also to make it
+		 * easy to generate sparse core files, use a helper that returns
+		 * NULL when encountering an empty page table entry that would
+		 * otherwise have been filled with the zero page.
+		 */
+		page = get_dump_page(addr);
+		if (page) {
+			void *kaddr = kmap(page);
+
+			stop = !dump_emit(cprm, kaddr, PAGE_SIZE);
+			kunmap(page);
+			put_page(page);
+		} else {
+			stop = !dump_skip(cprm, PAGE_SIZE);
+		}
+		if (stop)
+			return 0;
+	}
+	return 1;
+}
+#endif
+
+int dump_align(struct coredump_params *cprm, int align)
+{
+	unsigned mod = cprm->pos & (align - 1);
+	if (align & (align - 1))
+		return 0;
+	return mod ? dump_skip(cprm, align - mod) : 1;
+}
+EXPORT_SYMBOL(dump_align);
+
+/*
+ * Ensures that file size is big enough to contain the current file
+ * postion. This prevents gdb from complaining about a truncated file
+ * if the last "write" to the file was dump_skip.
+ */
+void dump_truncate(struct coredump_params *cprm)
+{
+	struct file *file = cprm->file;
+	loff_t offset;
+
+	if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
+		offset = file->f_op->llseek(file, 0, SEEK_CUR);
+		if (i_size_read(file->f_mapping->host) < offset)
+			do_truncate(file->f_path.dentry, offset, 0, file);
+	}
+}
+EXPORT_SYMBOL(dump_truncate);
+
+/*
+ * The purpose of always_dump_vma() is to make sure that special kernel mappings
+ * that are useful for post-mortem analysis are included in every core dump.
+ * In that way we ensure that the core dump is fully interpretable later
+ * without matching up the same kernel and hardware config to see what PC values
+ * meant. These special mappings include - vDSO, vsyscall, and other
+ * architecture specific mappings
+ */
+static bool always_dump_vma(struct vm_area_struct *vma)
+{
+	/* Any vsyscall mappings? */
+	if (vma == get_gate_vma(vma->vm_mm))
+		return true;
+
+	/*
+	 * Assume that all vmas with a .name op should always be dumped.
+	 * If this changes, a new vm_ops field can easily be added.
+	 */
+	if (vma->vm_ops && vma->vm_ops->name && vma->vm_ops->name(vma))
+		return true;
+
+	/*
+	 * arch_vma_name() returns non-NULL for special architecture mappings,
+	 * such as vDSO sections.
+	 */
+	if (arch_vma_name(vma))
+		return true;
+
+	return false;
+}
+
+#define DUMP_SIZE_MAYBE_ELFHDR_PLACEHOLDER 1
+
+/*
+ * Decide how much of @vma's contents should be included in a core dump.
+ */
+static unsigned long vma_dump_size(struct vm_area_struct *vma,
+				   unsigned long mm_flags)
+{
+#define FILTER(type)	(mm_flags & (1UL << MMF_DUMP_##type))
+
+	/* always dump the vdso and vsyscall sections */
+	if (always_dump_vma(vma))
+		goto whole;
+
+	if (vma->vm_flags & VM_DONTDUMP)
+		return 0;
+
+	/* support for DAX */
+	if (vma_is_dax(vma)) {
+		if ((vma->vm_flags & VM_SHARED) && FILTER(DAX_SHARED))
+			goto whole;
+		if (!(vma->vm_flags & VM_SHARED) && FILTER(DAX_PRIVATE))
+			goto whole;
+		return 0;
+	}
+
+	/* Hugetlb memory check */
+	if (is_vm_hugetlb_page(vma)) {
+		if ((vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_SHARED))
+			goto whole;
+		if (!(vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_PRIVATE))
+			goto whole;
+		return 0;
+	}
+
+	/* Do not dump I/O mapped devices or special mappings */
+	if (vma->vm_flags & VM_IO)
+		return 0;
+
+	/* By default, dump shared memory if mapped from an anonymous file. */
+	if (vma->vm_flags & VM_SHARED) {
+		if (file_inode(vma->vm_file)->i_nlink == 0 ?
+		    FILTER(ANON_SHARED) : FILTER(MAPPED_SHARED))
+			goto whole;
+		return 0;
+	}
+
+	/* Dump segments that have been written to.  */
+	if ((!IS_ENABLED(CONFIG_MMU) || vma->anon_vma) && FILTER(ANON_PRIVATE))
+		goto whole;
+	if (vma->vm_file == NULL)
+		return 0;
+
+	if (FILTER(MAPPED_PRIVATE))
+		goto whole;
+
+	/*
+	 * If this is the beginning of an executable file mapping,
+	 * dump the first page to aid in determining what was mapped here.
+	 */
+	if (FILTER(ELF_HEADERS) &&
+	    vma->vm_pgoff == 0 && (vma->vm_flags & VM_READ)) {
+		if ((READ_ONCE(file_inode(vma->vm_file)->i_mode) & 0111) != 0)
+			return PAGE_SIZE;
+
+		/*
+		 * ELF libraries aren't always executable.
+		 * We'll want to check whether the mapping starts with the ELF
+		 * magic, but not now - we're holding the mmap lock,
+		 * so copy_from_user() doesn't work here.
+		 * Use a placeholder instead, and fix it up later in
+		 * dump_vma_snapshot().
+		 */
+		return DUMP_SIZE_MAYBE_ELFHDR_PLACEHOLDER;
+	}
+
+#undef	FILTER
+
+	return 0;
+
+whole:
+	return vma->vm_end - vma->vm_start;
+}
+
+static struct vm_area_struct *first_vma(struct task_struct *tsk,
+					struct vm_area_struct *gate_vma)
+{
+	struct vm_area_struct *ret = tsk->mm->mmap;
+
+	if (ret)
+		return ret;
+	return gate_vma;
+}
+
+/*
+ * Helper function for iterating across a vma list.  It ensures that the caller
+ * will visit `gate_vma' prior to terminating the search.
+ */
+static struct vm_area_struct *next_vma(struct vm_area_struct *this_vma,
+				       struct vm_area_struct *gate_vma)
+{
+	struct vm_area_struct *ret;
+
+	ret = this_vma->vm_next;
+	if (ret)
+		return ret;
+	if (this_vma == gate_vma)
+		return NULL;
+	return gate_vma;
+}
+
+static void free_vma_snapshot(struct coredump_params *cprm)
+{
+	if (cprm->vma_meta) {
+		int i;
+		for (i = 0; i < cprm->vma_count; i++) {
+			struct file *file = cprm->vma_meta[i].file;
+			if (file)
+				fput(file);
+		}
+		kvfree(cprm->vma_meta);
+		cprm->vma_meta = NULL;
+	}
+}
+
+/*
+ * Under the mmap_lock, take a snapshot of relevant information about the task's
+ * VMAs.
+ */
+static bool dump_vma_snapshot(struct coredump_params *cprm)
+{
+	struct vm_area_struct *vma, *gate_vma;
+	struct mm_struct *mm = current->mm;
+	int i;
+
+	/*
+	 * Once the stack expansion code is fixed to not change VMA bounds
+	 * under mmap_lock in read mode, this can be changed to take the
+	 * mmap_lock in read mode.
+	 */
+	if (mmap_write_lock_killable(mm))
+		return false;
+
+	cprm->vma_data_size = 0;
+	gate_vma = get_gate_vma(mm);
+	cprm->vma_count = mm->map_count + (gate_vma ? 1 : 0);
+
+	cprm->vma_meta = kvmalloc_array(cprm->vma_count, sizeof(*cprm->vma_meta), GFP_KERNEL);
+	if (!cprm->vma_meta) {
+		mmap_write_unlock(mm);
+		return false;
+	}
+
+	for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
+			vma = next_vma(vma, gate_vma), i++) {
+		struct core_vma_metadata *m = cprm->vma_meta + i;
+
+		m->start = vma->vm_start;
+		m->end = vma->vm_end;
+		m->flags = vma->vm_flags;
+		m->dump_size = vma_dump_size(vma, cprm->mm_flags);
+		m->pgoff = vma->vm_pgoff;
+
+		m->file = vma->vm_file;
+		if (m->file)
+			get_file(m->file);
+	}
+
+	mmap_write_unlock(mm);
+
+	for (i = 0; i < cprm->vma_count; i++) {
+		struct core_vma_metadata *m = cprm->vma_meta + i;
+
+		if (m->dump_size == DUMP_SIZE_MAYBE_ELFHDR_PLACEHOLDER) {
+			char elfmag[SELFMAG];
+
+			if (copy_from_user(elfmag, (void __user *)m->start, SELFMAG) ||
+					memcmp(elfmag, ELFMAG, SELFMAG) != 0) {
+				m->dump_size = 0;
+			} else {
+				m->dump_size = PAGE_SIZE;
+			}
+		}
+
+		cprm->vma_data_size += m->dump_size;
+	}
+
+	return true;
+}