Re: [PATCH v7] seccomp, ptrace: add support for dumping seccomp filters
From: Oleg Nesterov <hidden>
Date: 2015-10-20 18:04:01
Also in:
lkml
Sorry for delay... On 10/13, Tycho Andersen wrote:
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--- a/include/uapi/linux/ptrace.h +++ b/include/uapi/linux/ptrace.h@@ -23,6 +23,8 @@ #define PTRACE_SYSCALL 24 +#define PTRACE_SECCOMP_GET_FILTER 40
Probably it would be better to add this at the end of other 0x42.. constants? After PTRACE_SETSIGMASK.
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--- a/kernel/seccomp.c +++ b/kernel/seccomp.c@@ -347,6 +347,7 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) { struct seccomp_filter *sfilter; int ret; + const bool save_orig = config_enabled(CONFIG_CHECKPOINT_RESTORE); if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) return ERR_PTR(-EINVAL);@@ -370,7 +371,7 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) return ERR_PTR(-ENOMEM); ret = bpf_prog_create_from_user(&sfilter->prog, fprog, - seccomp_check_filter, false); + seccomp_check_filter, save_orig);
Can't comment, this depends on other changes I missed... but I don't this you need my review here ;)
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+#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) +long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, + void __user *data) +{ + struct seccomp_filter *filter; + struct sock_fprog_kern *fprog; + long ret; + unsigned long count = 0; + + spin_lock_irq(¤t->sighand->siglock); + if (!capable(CAP_SYS_ADMIN) || + current->seccomp.mode != SECCOMP_MODE_DISABLED) { + ret = -EACCES; + goto out_self; + } + + spin_lock_irq(&task->sighand->siglock);
Oh, no, you can't do this. This is deadlockable. Suppose that this task's sub-thread traces the caller (the current task) and does PTRACE_SECCOMP_GET_FILTER too. In this case it can take the same 2 locks in reverse order, deadlock. But why do you need to hold both ->siglock's at the same time? Oleg.