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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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