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SubjectRe: i386-show-unhandled-signals-v3
On 7/25/07, Kirill Korotaev <dev@openvz.org> wrote:
> plz don't enable it by default... :/
> any user can spam syslog with these messages and if syslog is run as root
> can take the whole diskspace...


Yeah, but:
1) Right now (without this patch), it is enabled by default with _no_
rate control in _all_ kernels; I ran the tiny program that is here,
and it wasn't fun to watch.
2) With this patch it will be rate controlled using
printk_ratelimit(), thus reducing the amount of spam immensely.

Of course, we can disable both of them, is this what you (and
everybody else) want?

Masoud

> Thanks,
> Kirill
>
> Masoud Asgharifard Sharbiani wrote:
> > Hello,
> > This patch makes the i386 behave the same way that x86_64 does when a
> > segfault happens. A line gets printed to the kernel log so that tools
> > that
> > need to check for failures can behave more uniformly between
> > debug.show_unhandled_signals sysctl variable to 0 (or by doing echo 0 >
> > /proc/sys/debug/exception-trace)
> >
> > Also, all of the lines being printed are now using printk_ratelimit() to
> > deny the ability of DoS from a local user with a program like the
> > following:
> >
> > main()
> > {
> > while (1)
> > if (!fork()) *(int *)0 = 0;
> > }
> >
> > This new revision also includes the fix that Andrew did which got rid of
> > new sysctl that was added to the system in earlier versions of this.
> > Also, 'show-unhandled-signals' sysctl has been renamed back to the old
> > 'exception-trace' to avoid breakage of people's scripts.
> >
> > cheers,
> > Masoud Sharbiani
> >
> > Signed-off-by: Masoud Sharbiani <masouds@google.com>
> > Cc: Andi Kleen <ak@suse.de>
> >
> > ---
> > arch/i386/kernel/signal.c | 7 +++++++
> > arch/i386/kernel/traps.c | 7 +++++++
> > arch/i386/mm/fault.c | 10 ++++++++++
> > arch/x86_64/kernel/signal.c | 2 +-
> > arch/x86_64/kernel/traps.c | 6 ++++--
> > arch/x86_64/mm/fault.c | 15 +++------------
> > arch/x86_64/mm/init.c | 35 -----------------------------------
> > include/asm-x86_64/proto.h | 2 --
> > include/linux/signal.h | 3 +++
> > kernel/signal.c | 10 ++++++++++
> > kernel/sysctl.c | 10 ++++++++++
> > 11 files changed, 55 insertions(+), 52 deletions(-)
> >
> > diff --git a/arch/i386/kernel/signal.c b/arch/i386/kernel/signal.c
> > index d574e38..f5dd856 100644
> > --- a/arch/i386/kernel/signal.c
> > +++ b/arch/i386/kernel/signal.c
> > @@ -199,6 +199,13 @@ asmlinkage int sys_sigreturn(unsigned long __unused)
> > return eax;
> >
> > badframe:
> > + if (show_unhandled_signals && printk_ratelimit())
> > + printk("%s%s[%d] bad frame in sigreturn frame:%p eip:%lx"
> > + " esp:%lx oeax:%lx\n",
> > + current->pid > 1 ? KERN_INFO : KERN_EMERG,
> > + current->comm, current->pid, frame, regs->eip,
> > + regs->esp, regs->orig_eax);
> > +
> > force_sig(SIGSEGV, current);
> > return 0;
> > }
> > diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
> > index 18c1c28..c20283c 100644
> > --- a/arch/i386/kernel/traps.c
> > +++ b/arch/i386/kernel/traps.c
> > @@ -611,6 +611,13 @@ fastcall void __kprobes do_general_protection(struct pt_regs * regs,
> >
> > current->thread.error_code = error_code;
> > current->thread.trap_no = 13;
> > + if (show_unhandled_signals && unhandled_signal(current, SIGSEGV) &&
> > + printk_ratelimit())
> > + printk(KERN_INFO
> > + "%s[%d] general protection eip:%lx esp:%lx error:%lx\n",
> > + current->comm, current->pid,
> > + regs->eip, regs->esp, error_code);
> > +
> > force_sig(SIGSEGV, current);
> > return;
> >
> > diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c
> > index 1ecb3e4..52c940b 100644
> > --- a/arch/i386/mm/fault.c
> > +++ b/arch/i386/mm/fault.c
> > @@ -283,6 +283,8 @@ static inline int vmalloc_fault(unsigned long address)
> > return 0;
> > }
> >
> > +int show_unhandled_signals = 1;
> > +
> > /*
> > * This routine handles page faults. It determines the address,
> > * and the problem, and then passes it off to one of the appropriate
> > @@ -470,6 +472,14 @@ bad_area_nosemaphore:
> > if (is_prefetch(regs, address, error_code))
> > return;
> >
> > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
> > + printk_ratelimit()) {
> > + printk("%s%s[%d]: segfault at %08lx eip %08lx "
> > + "esp %08lx error %lx\n",
> > + tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
> > + tsk->comm, tsk->pid, address, regs->eip,
> > + regs->esp, error_code);
> > + }
> > tsk->thread.cr2 = address;
> > /* Kernel addresses are always protection faults */
> > tsk->thread.error_code = error_code | (address >= TASK_SIZE);
> > diff --git a/arch/x86_64/kernel/signal.c b/arch/x86_64/kernel/signal.c
> > index 290f5d8..f9506f6 100644
> > --- a/arch/x86_64/kernel/signal.c
> > +++ b/arch/x86_64/kernel/signal.c
> > @@ -480,7 +480,7 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
> > void signal_fault(struct pt_regs *regs, void __user *frame, char *where)
> > {
> > struct task_struct *me = current;
> > - if (exception_trace)
> > + if (show_unhandled_signals && printk_ratelimit())
> > printk("%s[%d] bad frame in %s frame:%p rip:%lx rsp:%lx orax:%lx\n",
> > me->comm,me->pid,where,frame,regs->rip,regs->rsp,regs->orig_rax);
> >
> > diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
> > index 74cbeb2..b9660c4 100644
> > --- a/arch/x86_64/kernel/traps.c
> > +++ b/arch/x86_64/kernel/traps.c
> > @@ -580,7 +580,8 @@ static void __kprobes do_trap(int trapnr, int signr, char *str,
> > tsk->thread.error_code = error_code;
> > tsk->thread.trap_no = trapnr;
> >
> > - if (exception_trace && unhandled_signal(tsk, signr))
> > + if (show_unhandled_signals && unhandled_signal(tsk, signr) &&
> > + printk_ratelimit())
> > printk(KERN_INFO
> > "%s[%d] trap %s rip:%lx rsp:%lx error:%lx\n",
> > tsk->comm, tsk->pid, str,
> > @@ -684,7 +685,8 @@ asmlinkage void __kprobes do_general_protection(struct pt_regs * regs,
> > tsk->thread.error_code = error_code;
> > tsk->thread.trap_no = 13;
> >
> > - if (exception_trace && unhandled_signal(tsk, SIGSEGV))
> > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
> > + printk_ratelimit())
> > printk(KERN_INFO
> > "%s[%d] general protection rip:%lx rsp:%lx error:%lx\n",
> > tsk->comm, tsk->pid,
> > diff --git a/arch/x86_64/mm/fault.c b/arch/x86_64/mm/fault.c
> > index 635e58d..0412824 100644
> > --- a/arch/x86_64/mm/fault.c
> > +++ b/arch/x86_64/mm/fault.c
> > @@ -221,16 +221,6 @@ static int is_errata93(struct pt_regs *regs, unsigned long address)
> > return 0;
> > }
> >
> > -int unhandled_signal(struct task_struct *tsk, int sig)
> > -{
> > - if (is_init(tsk))
> > - return 1;
> > - if (tsk->ptrace & PT_PTRACED)
> > - return 0;
> > - return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) ||
> > - (tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
> > -}
> > -
> > static noinline void pgtable_bad(unsigned long address, struct pt_regs *regs,
> > unsigned long error_code)
> > {
> > @@ -302,7 +292,7 @@ static int vmalloc_fault(unsigned long address)
> > }
> >
> > int page_fault_trace = 0;
> > -int exception_trace = 1;
> > +int show_unhandled_signals = 1;
> >
> > /*
> > * This routine handles page faults. It determines the address,
> > @@ -495,7 +485,8 @@ bad_area_nosemaphore:
> > (address >> 32))
> > return;
> >
> > - if (exception_trace && unhandled_signal(tsk, SIGSEGV)) {
> > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
> > + printk_ratelimit()) {
> > printk(
> > "%s%s[%d]: segfault at %016lx rip %016lx rsp %016lx error %lx\n",
> > tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
> > diff --git a/arch/x86_64/mm/init.c b/arch/x86_64/mm/init.c
> > index 9a0e98a..5096168 100644
> > --- a/arch/x86_64/mm/init.c
> > +++ b/arch/x86_64/mm/init.c
> > @@ -697,41 +697,6 @@ int kern_addr_valid(unsigned long addr)
> > return pfn_valid(pte_pfn(*pte));
> > }
> >
> > -#ifdef CONFIG_SYSCTL
> > -#include <linux/sysctl.h>
> > -
> > -extern int exception_trace, page_fault_trace;
> > -
> > -static ctl_table debug_table2[] = {
> > - {
> > - .ctl_name = 99,
> > - .procname = "exception-trace",
> > - .data = &exception_trace,
> > - .maxlen = sizeof(int),
> > - .mode = 0644,
> > - .proc_handler = proc_dointvec
> > - },
> > - {}
> > -};
> > -
> > -static ctl_table debug_root_table2[] = {
> > - {
> > - .ctl_name = CTL_DEBUG,
> > - .procname = "debug",
> > - .mode = 0555,
> > - .child = debug_table2
> > - },
> > - {}
> > -};
> > -
> > -static __init int x8664_sysctl_init(void)
> > -{
> > - register_sysctl_table(debug_root_table2);
> > - return 0;
> > -}
> > -__initcall(x8664_sysctl_init);
> > -#endif
> > -
> > /* A pseudo VMA to allow ptrace access for the vsyscall page. This only
> > covers the 64bit vsyscall page now. 32bit has a real VMA now and does
> > not need special handling anymore. */
> > diff --git a/include/asm-x86_64/proto.h b/include/asm-x86_64/proto.h
> > index 85255db..4fad501 100644
> > --- a/include/asm-x86_64/proto.h
> > +++ b/include/asm-x86_64/proto.h
> > @@ -75,8 +75,6 @@ extern void setup_node_bootmem(int nodeid, unsigned long start, unsigned long en
> > extern void early_quirks(void);
> > extern void check_efer(void);
> >
> > -extern int unhandled_signal(struct task_struct *tsk, int sig);
> > -
> > extern void select_idle_routine(const struct cpuinfo_x86 *c);
> >
> > extern unsigned long table_start, table_end;
> > diff --git a/include/linux/signal.h b/include/linux/signal.h
> > index ea91abe..0ae3388 100644
> > --- a/include/linux/signal.h
> > +++ b/include/linux/signal.h
> > @@ -237,12 +237,15 @@ extern int group_send_sig_info(int sig, struct siginfo *info, struct task_struct
> > extern int __group_send_sig_info(int, struct siginfo *, struct task_struct *);
> > extern long do_sigpending(void __user *, unsigned long);
> > extern int sigprocmask(int, sigset_t *, sigset_t *);
> > +extern int show_unhandled_signals;
> >
> > struct pt_regs;
> > extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie);
> >
> > extern struct kmem_cache *sighand_cachep;
> >
> > +int unhandled_signal(struct task_struct *tsk, int sig);
> > +
> > /*
> > * In POSIX a signal is sent either to a specific thread (Linux task)
> > * or to the process as a whole (Linux thread group). How the signal
> > diff --git a/kernel/signal.c b/kernel/signal.c
> > index 39d1227..ef8156a 100644
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -255,6 +255,16 @@ flush_signal_handlers(struct task_struct *t, int force_default)
> > }
> > }
> >
> > +int unhandled_signal(struct task_struct *tsk, int sig)
> > +{
> > + if (is_init(tsk))
> > + return 1;
> > + if (tsk->ptrace & PT_PTRACED)
> > + return 0;
> > + return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) ||
> > + (tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
> > +}
> > +
> >
> > /* Notify the system that a driver wants to block all signals for this
> > * process, and wants to be notified if any signals at all were to be
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index 7063ebc..af7002f 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -1153,6 +1153,16 @@ static ctl_table fs_table[] = {
> > };
> >
> > static ctl_table debug_table[] = {
> > +#ifdef CONFIG_X86
> > + {
> > + .ctl_name = CTL_UNNUMBERED,
> > + .procname = "exception-trace",
> > + .data = &show_unhandled_signals,
> > + .maxlen = sizeof(int),
> > + .mode = 0644,
> > + .proc_handler = proc_dointvec
> > + },
> > +#endif
> > { .ctl_name = 0 }
> > };
> >
> > -
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>
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