ptrace: Prepare to fix racy accesses on task breakpoints
authorFrederic Weisbecker <fweisbec@gmail.com>
Thu, 7 Apr 2011 14:53:20 +0000 (16:53 +0200)
committerFrederic Weisbecker <fweisbec@gmail.com>
Mon, 25 Apr 2011 15:28:24 +0000 (17:28 +0200)
commitbf26c018490c2fce7fe9b629083b96ce0e6ad019
treeff595f6268cb6fc675beb6accf6abb0701829443
parentf4929bd37208540c2c6f416e9035ff1938f2dbc6
ptrace: Prepare to fix racy accesses on task breakpoints

When a task is traced and is in a stopped state, the tracer
may execute a ptrace request to examine the tracee state and
get its task struct. Right after, the tracee can be killed
and thus its breakpoints released.
This can happen concurrently when the tracer is in the middle
of reading or modifying these breakpoints, leading to dereferencing
a freed pointer.

Hence, to prepare the fix, create a generic breakpoint reference
holding API. When a reference on the breakpoints of a task is
held, the breakpoints won't be released until the last reference
is dropped. After that, no more ptrace request on the task's
breakpoints can be serviced for the tracer.

Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: v2.6.33.. <stable@kernel.org>
Link: http://lkml.kernel.org/r/1302284067-7860-2-git-send-email-fweisbec@gmail.com
include/linux/ptrace.h
include/linux/sched.h
kernel/exit.c
kernel/ptrace.c