Re: [PATCH v2] arm: prevent BUG_ON in audit_syscall_entry()

Hi Akashi, On Tue, Sep 09, 2014 at 05:49:59AM +0100, AKASHI Takahiro wrote: > BUG_ON() in audit_syscall_entry() will be hit if user issues syscall(-1) > while syscall auditing is enabled (that is, by starting auditd). [...] > diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h > index f555bb3..de01145 100644 > --- a/arch/arm/include/asm/traps.h > +++ b/arch/arm/include/asm/traps.h > @@ -49,6 +49,7 @@ static inline int in_exception_text(unsigned long ptr) > extern void __init early_trap_init(void *); > extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame); > extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs); > +extern int arm_syscall(int no, struct pt_regs *regs); > > extern void *vectors_page; > > diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S > index e52fe5a..28d3931 100644 > --- a/arch/arm/kernel/entry-common.S > +++ b/arch/arm/kernel/entry-common.S > @@ -426,7 +426,6 @@ ENTRY(vector_swi) > local_restart: > ldr r10, [tsk, #TI_FLAGS] @ check for syscall tracing > stmdb sp!, {r4, r5} @ push fifth and sixth args > - You don't need this cosmetic change.

> tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls? > bne __sys_trace > > @@ -476,10 +475,11 @@ __sys_trace: > cmp scno, #-1 @ skip the syscall? > bne 2b > add sp, sp, #S_OFF @ restore stack > - b ret_slow_syscall > + b __sys_trace_return_skipped Can't you just remove the add as well, them fall-through here?

> > __sys_trace_return: > str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 > +__sys_trace_return_skipped: > mov r0, sp > bl syscall_trace_exit > b ret_slow_syscall > diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c > index 0c27ed6..68b42cd 100644 > --- a/arch/arm/kernel/ptrace.c > +++ b/arch/arm/kernel/ptrace.c > @@ -930,7 +930,9 @@ static void tracehook_report_syscall(struct pt_regs *regs, > > asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) > { > - current_thread_info()->syscall = scno; > + int orig_scno; > + > + current_thread_info()->syscall = orig_scno = scno; > > /* Do the secure computing check first; failures should be fast. */ > if (secure_computing(scno) == -1) > @@ -941,31 +943,40 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) > > scno = current_thread_info()->syscall; > > - if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) > - trace_sys_enter(regs, scno); > + if (scno >= 0 && scno < NR_syscalls) { Is this supposed to work for OABI? If so, better use __NR_SYSCALL_BASE.

#if defined(CONFIG_OABI_COMPAT) bics r10, r10, #0xff000000 eorne scno, r10, #__NR_OABI_SYSCALL_BASE ldrne tbl, =sys_oabi_call_table #elif !defined(CONFIG_AEABI) bic scno, scno, #0xff000000 @ mask off SWI op-code eor scno, scno, #__NR_SYSCALL_BASE @ check OS number #endif local_restart:

> + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) > + trace_sys_enter(regs, scno); > + > + audit_syscall_entry(AUDIT_ARCH_ARM, scno, > + regs->ARM_r0, regs->ARM_r1, > + regs->ARM_r2, regs->ARM_r3); > + } > > - audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1, > - regs->ARM_r2, regs->ARM_r3); > + /* user-issued syscall of -1 */ > + if (scno == -1 && orig_scno == -1) Make this an else if, for clarity?

> + arm_syscall(scno, regs); Doesn't this always result in bad_syscall being called, which sends a SIGILL to the task? Shouldn't we simply return -ENOSYS instead? You could do that in the assembly code.

> return scno; > } > > asmlinkage void syscall_trace_exit(struct pt_regs *regs) > { > - /* > - * Audit the syscall before anything else, as a debugger may > - * come in and change the current registers. > - */ > - audit_syscall_exit(regs); > + if (current_thread_info()->syscall < NR_syscalls) { Again, not going to work for OABI.

Will