[tip:perf/urgent] arm, hw_breakpoints: Fix racy access to ptrace breakpoints

From: tip-bot for Frederic Weisbecker
Date: Wed May 04 2011 - 16:30:29 EST


Commit-ID: bf0b8f4b55e591ba417c2dbaff42769e1fc773b0
Gitweb: http://git.kernel.org/tip/bf0b8f4b55e591ba417c2dbaff42769e1fc773b0
Author: Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Fri, 8 Apr 2011 17:29:36 +0200
Committer: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CommitDate: Mon, 25 Apr 2011 17:35:18 +0200

arm, hw_breakpoints: Fix racy access to ptrace breakpoints

While the tracer accesses ptrace breakpoints, the child task may
concurrently exit due to a SIGKILL and thus release its breakpoints
at the same time. We can then dereference some freed pointers.

To fix this, hold a reference on the child breakpoints before
manipulating them.

Reported-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Prasad <prasad@xxxxxxxxxxxxxxxxxx>
Cc: Paul Mundt <lethal@xxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1302284067-7860-5-git-send-email-fweisbec@xxxxxxxxx
---
arch/arm/kernel/ptrace.c | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 2bf27f3..8182f45 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -767,12 +767,20 @@ long arch_ptrace(struct task_struct *child, long request,

#ifdef CONFIG_HAVE_HW_BREAKPOINT
case PTRACE_GETHBPREGS:
+ if (ptrace_get_breakpoints(child) < 0)
+ return -ESRCH;
+
ret = ptrace_gethbpregs(child, addr,
(unsigned long __user *)data);
+ ptrace_put_breakpoints(child);
break;
case PTRACE_SETHBPREGS:
+ if (ptrace_get_breakpoints(child) < 0)
+ return -ESRCH;
+
ret = ptrace_sethbpregs(child, addr,
(unsigned long __user *)data);
+ ptrace_put_breakpoints(child);
break;
#endif

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/