On Tue, 2011-06-07 at 19:19 +0200, Oleg Nesterov wrote:

On 06/03, Eric Paris wrote:

quoted

The audit system previously expected arches calling to audit_syscall_exit to
supply as arguments if the syscall was a success and what the return code was.
Audit also provides a helper AUDITSC_RESULT which was supposed to simplify things
by converting from negative retcodes to an audit internal magic value stating
success or failure.  This helper was wrong and could indicate that a valid
pointer returned to userspace was a failed syscall.  The fix is to fix the
layering foolishness.  We now pass audit_syscall_exit a struct pt_reg and it
in turns calls back into arch code to collect the return value and to
determine if the syscall was a success or failure.  We also define a generic
is_syscall_success() macro which determines success/failure based on if the
value is < -MAX_ERRNO.  This works for arches like x86 which do not use a
separate mechanism to indicate syscall failure.

I know nothing about audit, but the patch looks fine to me.


But I have a bit off-topic question,

quoted

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 8a445a0..b7b1f88 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S

@@ -53,6 +53,7 @@
 #include <asm/paravirt.h>
 #include <asm/ftrace.h>
 #include <asm/percpu.h>
+#include <linux/err.h>

 /* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this.  */
 #include <linux/elf-em.h>

@@ -564,17 +565,16 @@ auditsys:
 	jmp system_call_fastpath

 	/*
-	 * Return fast path for syscall audit.  Call audit_syscall_exit()
+	 * Return fast path for syscall audit.  Call __audit_syscall_exit()
 	 * directly and then jump back to the fast path with TIF_SYSCALL_AUDIT
 	 * masked off.
 	 */
 sysret_audit:
 	movq RAX-ARGOFFSET(%rsp),%rsi	/* second arg, syscall return value */
-	cmpq $0,%rsi		/* is it < 0? */
-	setl %al		/* 1 if so, 0 if not */
+	cmpq $-MAX_ERRNO,%rsi	/* is it < -MAX_ERRNO? */
+	setbe %al		/* 1 if so, 0 if not */
 	movzbl %al,%edi		/* zero-extend that into %edi */
-	inc %edi /* first arg, 0->1(AUDITSC_SUCCESS), 1->2(AUDITSC_FAILURE) */
-	call audit_syscall_exit
+	call __audit_syscall_exit

With or without this patch, can't we call audit_syscall_exit() twice
if there is something else in _TIF_WORK_SYSCALL_EXIT mask apart from
SYSCALL_AUDIT ? First time it is called from asm, then from
syscall_trace_leave(), no?

For example. The task has TIF_SYSCALL_AUDIT and nothing else, it does
system_call->auditsys->system_call_fastpath. What if it gets, say,
TIF_SYSCALL_TRACE before ret_from_sys_call?

No harm is done calling twice.  The first call will do the real work and
cleanup.  It will set a flag in the audit data that the work has been
done (in_syscall == 0) thus the second call will then not do any real
work and won't have anything to clean up.

-Eric