2009-04-29 09:13:07

by Oleg Nesterov

Subject: [PATCH] elf_core_dump: use rcu_read_lock() to access ->real_parent

(on top of ptrace-s-parent-real_parent-in-binfmt_elf_fdpicc.patch)

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 <[email protected]>

fs/binfmt_elf.c | 8 ++++++--
fs/binfmt_elf_fdpic.c | 8 ++++++--
2 files changed, 12 insertions(+), 4 deletions(-)

--- PTRACE/fs/binfmt_elf.c~RCU_PARENT 2009-04-06 00:03:40.000000000 +0200
+++ PTRACE/fs/binfmt_elf.c 2009-04-29 10:46:54.000000000 +0200
@@ -1340,8 +1340,10 @@ static void fill_prstatus(struct elf_prs
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_prpsin
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);

--- PTRACE/fs/binfmt_elf_fdpic.c~RCU_PARENT 2009-04-28 21:40:49.000000000 +0200
+++ PTRACE/fs/binfmt_elf_fdpic.c 2009-04-29 10:52:31.000000000 +0200
@@ -1387,8 +1387,10 @@ static void fill_prstatus(struct elf_prs
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_prpsin
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);

2009-04-29 19:47:48

by Roland McGrath

Subject: Re: [PATCH] elf_core_dump: use rcu_read_lock() to access ->real_parent

Acked-by: Roland McGrath <[email protected]>