[PATCH 09/10] pidfs: record the coredump on the dumping thread's pid too

[Christian Brauner]

If a thread-group coredumps only the thread-group leader pidfd will
return coredump information. A pidfd for the thread that took the fatal
signal cannot be used to retrieve it.

Record both the thread-group leader and the specific thread that took
the signal and register both in pidfs. Mark both the thread-group leader
and the specific thread with the coredump information so retrieval works
for both pidfds.

Now that both SO_PEERPIDFD and SO_PEERPIDFD_THREAD are available it's
easy to get the coredump information for the specific thread.

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 fs/coredump.c            | 22 +++++++++++++---------
 fs/pidfs.c               | 11 +++++++++--
 include/linux/coredump.h |  4 +++-
 3 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 71a0093ada1b..b5ff4b3e1831 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -454,7 +454,7 @@ static bool coredump_parse(struct core_name *cn, struct coredump_params *cprm,
 				 * leader we know that the thread-group leader
 				 * cannot be reaped until @current has exited.
 				 */
-				cprm->pid = task_tgid(current);
+				task_pids(cprm->pid, current);
 				err = cn_printf(cn, "%d", COREDUMP_PIDFD_NUMBER);
 				break;
 			}
@@ -626,13 +626,17 @@ static int umh_coredump_setup(struct subprocess_info *info, struct cred *new)
 	struct coredump_params *cp = (struct coredump_params *)info->data;
 	int err;
 
-	if (cp->pid) {
+	if (cp->pid[PIDTYPE_TGID]) {
 		struct file *pidfs_file __free(fput) = NULL;
 
-		pidfs_file = pidfs_alloc_file(cp->pid, 0);
+		pidfs_file = pidfs_alloc_file(cp->pid[PIDTYPE_TGID], 0);
 		if (IS_ERR(pidfs_file))
 			return PTR_ERR(pidfs_file);
 
+		err = pidfs_register_pids(cp->pid);
+		if (err)
+			return err;
+
 		pidfs_coredump(cp);
 
 		/*
@@ -695,12 +699,12 @@ static bool coredump_sock_connect(struct core_name *cn, struct coredump_params *
 		return false;
 
 	/*
-	 * Set the thread-group leader pid which is used for the peer
-	 * credentials during connect() below. Then immediately register
-	 * it in pidfs...
+	 * Set the pids of the dumping thread and its thread-group leader
+	 * which are used for the peer credentials during connect() below.
+	 * Then immediately register them in pidfs...
 	 */
-	cprm->pid = task_tgid(current);
-	retval = pidfs_register_pid(cprm->pid);
+	task_pids(cprm->pid, current);
+	retval = pidfs_register_pids(cprm->pid);
 	if (retval)
 		return false;
 
@@ -722,7 +726,7 @@ static bool coredump_sock_connect(struct core_name *cn, struct coredump_params *
 	}
 
 	/* ... and validate that @sk_peer_pid matches @cprm.pid. */
-	if (WARN_ON_ONCE(unix_peer(socket->sk)->sk_peer_pid[PIDTYPE_TGID] != cprm->pid))
+	if (WARN_ON_ONCE(!pids_equal(unix_peer(socket->sk)->sk_peer_pid, cprm->pid)))
 		return false;
 
 	cprm->limit = RLIM_INFINITY;
diff --git a/fs/pidfs.c b/fs/pidfs.c
index 586af2e5811c..29299b2c7ca7 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -793,9 +793,9 @@ void pidfs_exit(struct task_struct *tsk)
 }
 
 #ifdef CONFIG_COREDUMP
-void pidfs_coredump(const struct coredump_params *cprm)
+static void pidfs_coredump_pid(struct pid *pid,
+			       const struct coredump_params *cprm)
 {
-	struct pid *pid = cprm->pid;
 	struct pidfs_attr *attr;
 
 	attr = READ_ONCE(pid->attr);
@@ -814,6 +814,13 @@ void pidfs_coredump(const struct coredump_params *cprm)
 	smp_wmb();
 	set_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask);
 }
+
+void pidfs_coredump(const struct coredump_params *cprm)
+{
+	/* The dumping thread's pidfd reports the coredump as well. */
+	for (enum pid_type type = PIDTYPE_PID; type <= pids_last(cprm->pid); type++)
+		pidfs_coredump_pid(cprm->pid[type], cprm);
+}
 #endif
 
 static struct vfsmount *pidfs_mnt __ro_after_init;
diff --git a/include/linux/coredump.h b/include/linux/coredump.h
index 7b38ee2e7913..0bbb7de6a402 100644
--- a/include/linux/coredump.h
+++ b/include/linux/coredump.h
@@ -5,6 +5,7 @@
 #include <linux/types.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
+#include <linux/pid_types.h>
 #include <linux/sched/coredump.h>
 #include <asm/siginfo.h>
 
@@ -32,7 +33,8 @@ struct coredump_params {
 	int vma_count;
 	size_t vma_data_size;
 	struct core_vma_metadata *vma_meta;
-	struct pid *pid;
+	/* Dumping thread and its thread-group leader by pid type. */
+	DECLARE_PIDS(pid, PIDTYPE_TGID);
 };
 
 extern unsigned int core_file_note_size_limit;

-- 
2.53.0