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    SubjectRe: i386-show-unhandled-signals-v3
    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...

    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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