[PATCH] make vm86 call audit_syscall_exit (7e7f8a03) · Commits · 戴 / test

hi, The motivation behind the patch below was to address messages in /var/log/messages such as: Jan 31 10:54:15 mets kernel: audit(:0): major=252 name_count=0: freeing multiple contexts (1) Jan 31 10:54:15 mets kernel: audit(:0): major=113 name_count=0: freeing multiple contexts (2) I can reproduce by running 'get-edid' from: http://john.fremlin.de/programs/linux/read-edid/ . These messages come about in the log b/c the vm86 calls do not exit via the normal system call exit paths and thus do not call 'audit_syscall_exit'. The next system call will then free the context for itself and for the vm86 context, thus generating the above messages. This patch addresses the issue by simply adding a call to 'audit_syscall_exit' from the vm86 code. Besides fixing the above error messages the patch also now allows vm86 system calls to become auditable. This is useful since strace does not appear to properly record the return values from sys_vm86. I think this patch is also a step in the right direction in terms of cleaning up some core auditing code. If we can correct any other paths that do not properly call the audit exit and entries points, then we can also eliminate the notion of context chaining. I've tested this patch by verifying that the log messages no longer appear, and that the audit records for sys_vm86 appear to be correct. Also, 'read_edid' produces itentical output. thanks, -Jason Signed-off-by:

Jason Baron <jbaron@redhat.com> Signed-off-by:

Al Viro <viro@zeniv.linux.org.uk>

arch/i386/kernel/vm86.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -43,6 +43,7 @@
		#include <linux/smp_lock.h>
		#include <linux/highmem.h>
		#include <linux/ptrace.h>
		#include <linux/audit.h>

		#include <asm/uaccess.h>
		#include <asm/io.h>
		@@ -252,6 +253,7 @@ out:
		static void do_sys_vm86(struct kernel_vm86_struct info, struct task_struct tsk)
		{
		struct tss_struct *tss;
		long eax;
		/*
		* make sure the vm86() system call doesn't try to do anything silly
		*/
		@@ -305,13 +307,19 @@ static void do_sys_vm86(struct kernel_vm86_struct info, struct task_struct tsk
		tsk->thread.screen_bitmap = info->screen_bitmap;
		if (info->flags & VM86_SCREEN_BITMAP)
		mark_screen_rdonly(tsk->mm);
		__asm__ __volatile__("xorl %eax,%eax; movl %eax,%fs; movl %eax,%gs\n\t");
		__asm__ __volatile__("movl %%eax, %0\n" :"=r"(eax));

		/call audit_syscall_exit since we do not exit via the normal paths /
		if (unlikely(current->audit_context))
		audit_syscall_exit(current, AUDITSC_RESULT(eax), eax);

		__asm__ __volatile__(
		"xorl %%eax,%%eax; movl %%eax,%%fs; movl %%eax,%%gs\n\t"
		"movl %0,%%esp\n\t"
		"movl %1,%%ebp\n\t"
		"jmp resume_userspace"
		: /* no outputs */
		:"r" (&info->regs), "r" (task_thread_info(tsk)) : "ax");
		:"r" (&info->regs), "r" (task_thread_info(tsk)));
		/* we never return here */
		}

kernel/auditsc.c

+0 −5

Original line number	Diff line number	Diff line
		@@ -966,11 +966,6 @@ void audit_syscall_entry(struct task_struct *tsk, int arch, int major,
		if (context->in_syscall) {
		struct audit_context *newctx;

		#if defined(__NR_vm86) && defined(__NR_vm86old)
		/* vm86 mode should only be entered once */
		if (major == __NR_vm86 \|\| major == __NR_vm86old)
		return;
		#endif
		#if AUDIT_DEBUG
		printk(KERN_ERR
		"audit(:%d) pid=%d in syscall=%d;"

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