Messages in this thread Patch in this message | | | Date | Sun, 23 Mar 2008 16:51:10 +0300 | From | Oleg Nesterov <> | Subject | [PATCH] ptrace: it is fun to strace /sbin/init |
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(re-send with updated changelog)
Ptracing of /sbin/init is not allowed. Of course, this is dangerous, but may be useful. Introduce the kernel boot parameter to allow this, so that we can't surprise some special/secured systems.
Afaics, with the recent changes there is no kernel problems with ptracing init, it can't lose SIGNAL_UNKILLABLE flag and be killed by accident. However, admin should know what it does, "gdb /sbin/init 1" stops init, it can't reap zombies or take care of /etc/inittab until continued. It is even possible to crash init (and thus the whole system) if you wish, ptracer has full control.
The "if (pid == 1)" check in ptrace_get_task_struct() is killed, ptrace_attach does the same check.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- 25/kernel/ptrace.c~5_INIT_PTRACE 2008-03-16 17:22:04.000000000 +0300 +++ 25/kernel/ptrace.c 2008-03-16 18:33:02.000000000 +0300 @@ -160,6 +160,15 @@ int ptrace_may_attach(struct task_struct return !err; } +static int allow_ptrace_init; + +static int __init __allow_ptrace_init(char *str) +{ + allow_ptrace_init = 1; + return 1; +} +__setup("init_ptrace", __allow_ptrace_init); + int ptrace_attach(struct task_struct *task) { int retval; @@ -168,7 +177,7 @@ int ptrace_attach(struct task_struct *ta audit_ptrace(task); retval = -EPERM; - if (task->pid <= 1) + if (unlikely(is_global_init(task)) && likely(!allow_ptrace_init)) goto out; if (same_thread_group(task, current)) goto out; @@ -518,12 +527,6 @@ struct task_struct *ptrace_get_task_stru { struct task_struct *child; - /* - * Tracing init is not allowed. - */ - if (pid == 1) - return ERR_PTR(-EPERM); - read_lock(&tasklist_lock); child = find_task_by_vpid(pid); if (child) --- 25/Documentation/kernel-parameters.txt~5_INIT_PTRACE 2008-02-15 16:58:12.000000000 +0300 +++ 25/Documentation/kernel-parameters.txt 2008-03-16 18:30:28.000000000 +0300 @@ -803,6 +803,8 @@ and is between 256 and 4096 characters. Run specified binary instead of /sbin/init as init process. + init_ptrace [KNL] Allows to ptrace init. + initcall_debug [KNL] Trace initcalls as they are executed. Useful for working out where the kernel is dying during startup.
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