From bf26c018490c2fce7fe9b629083b96ce0e6ad019 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 7 Apr 2011 16:53:20 +0200 Subject: [PATCH 1/5] 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 Signed-off-by: Frederic Weisbecker Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Prasad Cc: Paul Mundt Cc: v2.6.33.. Link: http://lkml.kernel.org/r/1302284067-7860-2-git-send-email-fweisbec@gmail.com --- include/linux/ptrace.h | 13 ++++++++++++- include/linux/sched.h | 3 +++ kernel/exit.c | 2 +- kernel/ptrace.c | 17 +++++++++++++++++ 4 files changed, 33 insertions(+), 2 deletions(-) diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index a1147e5dd245..9178d5cc0b01 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -189,6 +189,10 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace) child->ptrace = current->ptrace; __ptrace_link(child, current->parent); } + +#ifdef CONFIG_HAVE_HW_BREAKPOINT + atomic_set(&child->ptrace_bp_refcnt, 1); +#endif } /** @@ -350,6 +354,13 @@ extern int task_current_syscall(struct task_struct *target, long *callno, unsigned long args[6], unsigned int maxargs, unsigned long *sp, unsigned long *pc); -#endif +#ifdef CONFIG_HAVE_HW_BREAKPOINT +extern int ptrace_get_breakpoints(struct task_struct *tsk); +extern void ptrace_put_breakpoints(struct task_struct *tsk); +#else +static inline void ptrace_put_breakpoints(struct task_struct *tsk) { } +#endif /* CONFIG_HAVE_HW_BREAKPOINT */ + +#endif /* __KERNEL */ #endif diff --git a/include/linux/sched.h b/include/linux/sched.h index 18d63cea2848..781abd137673 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1537,6 +1537,9 @@ struct task_struct { unsigned long memsw_nr_pages; /* uncharged mem+swap usage */ } memcg_batch; #endif +#ifdef CONFIG_HAVE_HW_BREAKPOINT + atomic_t ptrace_bp_refcnt; +#endif }; /* Future-safe accessor for struct task_struct's cpus_allowed. */ diff --git a/kernel/exit.c b/kernel/exit.c index f5d2f63bae0b..8dd874181542 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1016,7 +1016,7 @@ NORET_TYPE void do_exit(long code) /* * FIXME: do that only when needed, using sched_exit tracepoint */ - flush_ptrace_hw_breakpoint(tsk); + ptrace_put_breakpoints(tsk); exit_notify(tsk, group_dead); #ifdef CONFIG_NUMA diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 0fc1eed28d27..dc7ab65f3b36 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -22,6 +22,7 @@ #include #include #include +#include /* @@ -879,3 +880,19 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid, return ret; } #endif /* CONFIG_COMPAT */ + +#ifdef CONFIG_HAVE_HW_BREAKPOINT +int ptrace_get_breakpoints(struct task_struct *tsk) +{ + if (atomic_inc_not_zero(&tsk->ptrace_bp_refcnt)) + return 0; + + return -1; +} + +void ptrace_put_breakpoints(struct task_struct *tsk) +{ + if (atomic_dec_and_test(&tsk->ptrace_bp_refcnt)) + flush_ptrace_hw_breakpoint(tsk); +} +#endif /* CONFIG_HAVE_HW_BREAKPOINT */ From 87dc669ba25777b67796d7262c569429e58b1ed4 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 Apr 2011 17:29:36 +0200 Subject: [PATCH 2/5] x86, 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 Signed-off-by: Frederic Weisbecker Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Prasad Cc: Paul Mundt Cc: v2.6.33.. Link: http://lkml.kernel.org/r/1302284067-7860-3-git-send-email-fweisbec@gmail.com --- arch/x86/kernel/ptrace.c | 36 ++++++++++++++++++++++++++---------- 1 file changed, 26 insertions(+), 10 deletions(-) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 45892dc4b72a..f65e5b521dbd 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -608,6 +608,9 @@ static int ptrace_write_dr7(struct task_struct *tsk, unsigned long data) unsigned len, type; struct perf_event *bp; + if (ptrace_get_breakpoints(tsk) < 0) + return -ESRCH; + data &= ~DR_CONTROL_RESERVED; old_dr7 = ptrace_get_dr7(thread->ptrace_bps); restore: @@ -655,6 +658,9 @@ restore: } goto restore; } + + ptrace_put_breakpoints(tsk); + return ((orig_ret < 0) ? orig_ret : rc); } @@ -668,10 +674,17 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n) if (n < HBP_NUM) { struct perf_event *bp; + + if (ptrace_get_breakpoints(tsk) < 0) + return -ESRCH; + bp = thread->ptrace_bps[n]; if (!bp) - return 0; - val = bp->hw.info.address; + val = 0; + else + val = bp->hw.info.address; + + ptrace_put_breakpoints(tsk); } else if (n == 6) { val = thread->debugreg6; } else if (n == 7) { @@ -686,6 +699,10 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr, struct perf_event *bp; struct thread_struct *t = &tsk->thread; struct perf_event_attr attr; + int err = 0; + + if (ptrace_get_breakpoints(tsk) < 0) + return -ESRCH; if (!t->ptrace_bps[nr]) { ptrace_breakpoint_init(&attr); @@ -709,24 +726,23 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr, * writing for the user. And anyway this is the previous * behaviour. */ - if (IS_ERR(bp)) - return PTR_ERR(bp); + if (IS_ERR(bp)) { + err = PTR_ERR(bp); + goto put; + } t->ptrace_bps[nr] = bp; } else { - int err; - bp = t->ptrace_bps[nr]; attr = bp->attr; attr.bp_addr = addr; err = modify_user_hw_breakpoint(bp, &attr); - if (err) - return err; } - - return 0; +put: + ptrace_put_breakpoints(tsk); + return err; } /* From 07fa7a0a8a586c01a8b416358c7012dcb9dc688d Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 Apr 2011 17:29:36 +0200 Subject: [PATCH 3/5] powerpc, 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 Signed-off-by: Frederic Weisbecker Acked-by: Prasad Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Paul Mundt Cc: v2.6.33.. Link: http://lkml.kernel.org/r/1302284067-7860-4-git-send-email-fweisbec@gmail.com --- arch/powerpc/kernel/ptrace.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c index 55613e33e263..4edeeb325429 100644 --- a/arch/powerpc/kernel/ptrace.c +++ b/arch/powerpc/kernel/ptrace.c @@ -1591,7 +1591,10 @@ long arch_ptrace(struct task_struct *child, long request, } case PTRACE_SET_DEBUGREG: + if (ptrace_get_breakpoints(child) < 0) + return -ESRCH; ret = ptrace_set_debugreg(child, addr, data); + ptrace_put_breakpoints(child); break; #ifdef CONFIG_PPC64 From bf0b8f4b55e591ba417c2dbaff42769e1fc773b0 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 Apr 2011 17:29:36 +0200 Subject: [PATCH 4/5] 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 Signed-off-by: Frederic Weisbecker Acked-by: Will Deacon Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Prasad Cc: Paul Mundt Link: http://lkml.kernel.org/r/1302284067-7860-5-git-send-email-fweisbec@gmail.com --- arch/arm/kernel/ptrace.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 2bf27f364d09..8182f45ca493 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 From e0ac8457d020c0289ea566917267da9e5e6d9865 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 Apr 2011 17:29:36 +0200 Subject: [PATCH 5/5] sh, 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 Signed-off-by: Frederic Weisbecker Acked-by: Paul Mundt Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Prasad Link: http://lkml.kernel.org/r/1302284067-7860-6-git-send-email-fweisbec@gmail.com --- arch/sh/kernel/ptrace_32.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/sh/kernel/ptrace_32.c b/arch/sh/kernel/ptrace_32.c index 2130ca674e9b..3d7b209b2178 100644 --- a/arch/sh/kernel/ptrace_32.c +++ b/arch/sh/kernel/ptrace_32.c @@ -117,7 +117,11 @@ void user_enable_single_step(struct task_struct *child) set_tsk_thread_flag(child, TIF_SINGLESTEP); + if (ptrace_get_breakpoints(child) < 0) + return; + set_single_step(child, pc); + ptrace_put_breakpoints(child); } void user_disable_single_step(struct task_struct *child)