elf_core_dump: use rcu_read_lock() to access ->real_parent

In theory it is not safe to dereference ->parent/real_parent without
tasklist or rcu lock, we can race with re-parenting.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 12 insertions, 4 deletions

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 40381df34869..9fa212b014a5 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1340,8 +1340,10 @@ static void fill_prstatus(struct elf_prstatus *prstatus,
         prstatus->pr_info.si_signo = prstatus->pr_cursig = signr;
         prstatus->pr_sigpend = p->pending.signal.sig[0];
         prstatus->pr_sighold = p->blocked.sig[0];
+        rcu_read_lock();
+        prstatus->pr_ppid = task_pid_vnr(rcu_dereference(p->real_parent));
+        rcu_read_unlock();
         prstatus->pr_pid = task_pid_vnr(p);
-        prstatus->pr_ppid = task_pid_vnr(p->real_parent);
         prstatus->pr_pgrp = task_pgrp_vnr(p);
         prstatus->pr_sid = task_session_vnr(p);
         if (thread_group_leader(p)) {
@@ -1382,8 +1384,10 @@ static int fill_psinfo(struct elf_prpsinfo *psinfo, struct task_struct *p,
                         psinfo->pr_psargs[i] = ' ';
         psinfo->pr_psargs[len] = 0;
 
+        rcu_read_lock();
+        psinfo->pr_ppid = task_pid_vnr(rcu_dereference(p->real_parent));
+        rcu_read_unlock();
         psinfo->pr_pid = task_pid_vnr(p);
-        psinfo->pr_ppid = task_pid_vnr(p->real_parent);
         psinfo->pr_pgrp = task_pgrp_vnr(p);
         psinfo->pr_sid = task_session_vnr(p);
 
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index fdb66faa24f1..20fbeced472b 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1387,8 +1387,10 @@ static void fill_prstatus(struct elf_prstatus *prstatus,
         prstatus->pr_info.si_signo = prstatus->pr_cursig = signr;
         prstatus->pr_sigpend = p->pending.signal.sig[0];
         prstatus->pr_sighold = p->blocked.sig[0];
+        rcu_read_lock();
+        prstatus->pr_ppid = task_pid_vnr(rcu_dereference(p->real_parent));
+        rcu_read_unlock();
         prstatus->pr_pid = task_pid_vnr(p);
-        prstatus->pr_ppid = task_pid_vnr(p->real_parent);
         prstatus->pr_pgrp = task_pgrp_vnr(p);
         prstatus->pr_sid = task_session_vnr(p);
         if (thread_group_leader(p)) {
@@ -1432,8 +1434,10 @@ static int fill_psinfo(struct elf_prpsinfo *psinfo, struct task_struct *p,
                         psinfo->pr_psargs[i] = ' ';
         psinfo->pr_psargs[len] = 0;
 
+        rcu_read_lock();
+        psinfo->pr_ppid = task_pid_vnr(rcu_dereference(p->real_parent));
+        rcu_read_unlock();
         psinfo->pr_pid = task_pid_vnr(p);
-        psinfo->pr_ppid = task_pid_vnr(p->real_parent);
         psinfo->pr_pgrp = task_pgrp_vnr(p);
         psinfo->pr_sid = task_session_vnr(p);