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ptrace: fix exit_ptrace() vs ptrace_traceme() race
Pointed out by Roland. The bug was recently introduced by me in
"forget_original_parent: split out the un-ptrace part", commit
39c626ae47
.
Since that patch we have a window after exit_ptrace() drops tasklist and
before forget_original_parent() takes it again. In this window the child
can do ptrace(PTRACE_TRACEME) and nobody can untrace this child after
that.
Change ptrace_traceme() to not attach to the exiting ->real_parent. We
don't report the error in this case, we pretend we attach right before
->real_parent calls exit_ptrace() which should untrace us anyway.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
7b102d034c
commit
f1671f6d78
@ -604,10 +604,11 @@ repeat:
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ret = security_ptrace_traceme(current->parent);
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/*
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* Set the ptrace bit in the process ptrace flags.
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* Then link us on our parent's ptraced list.
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* Check PF_EXITING to ensure ->real_parent has not passed
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* exit_ptrace(). Otherwise we don't report the error but
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* pretend ->real_parent untraces us right after return.
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*/
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if (!ret) {
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if (!ret && !(current->real_parent->flags & PF_EXITING)) {
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current->ptrace |= PT_PTRACED;
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__ptrace_link(current, current->real_parent);
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}
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