From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946012AbXBICpX (ORCPT ); Thu, 8 Feb 2007 21:45:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1946025AbXBICpX (ORCPT ); Thu, 8 Feb 2007 21:45:23 -0500 Received: from alpha.polcom.net ([217.79.150.67]:40821 "EHLO alpha.polcom.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946012AbXBICpW (ORCPT ); Thu, 8 Feb 2007 21:45:22 -0500 X-Greylist: delayed 1119 seconds by postgrey-1.27 at vger.kernel.org; Thu, 08 Feb 2007 21:45:22 EST Date: Fri, 9 Feb 2007 03:26:42 +0100 (CET) From: Grzegorz Kulewski To: linux-kernel@vger.kernel.org Subject: Strange oops in iret_exc with my own module Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, I written really simple and stupid module (the design wasn't mine). One tester of this module provided me the following oops it caused quite often (on many automated tests): [17179765.492000] BUG: unable to handle kernel NULL pointer dereference at virtual address 00000000 [17179765.492000] printing eip: [17179765.492000] c02c4845 [17179765.492000] *pde = 00000000 [17179765.492000] Oops: 0002 [#1] [17179765.492000] Modules linked in: altpinfo rfcomm l2cap bluetooth ppdev cpufreq_userspace cpufreq_stats freq_table cpufreq_powersave cpufreq_ondemand cpufreq_conservative video button battery container ac af_packet dm_mod md_mod ipv6 lp snd_seq_dummy snd_seq_oss snd_seq_midi snd_seq_midi_event snd_seq snd_via82xx gameport snd_ac97_codec snd_ac97_bus via686a snd_pcm_oss snd_mixer_oss tsdev i2c_isa i2c_viapro usbhid snd_pcm snd_timer snd_page_alloc snd_mpu401_uart snd_rawmidi snd_seq_device i2c_core snd soundcore psmouse 8139too mii pcspkr floppy serio_raw parport_pc rtc via_agp agpgart parport shpchp pci_hotplug evdev ext3 jbd mbcache ide_generic uhci_hcd usbcore ide_cd cdrom ide_disk via82cxxx generic thermal processor fan vga16fb cfbcopyarea vgastate cfbimgblt cfbfillrect [17179765.492000] CPU: 0 [17179765.492000] EIP: 0060:[] Not tainted VLI [17179765.492000] EFLAGS: 00210246 (2.6.17.13nopreempt #3) [17179765.492000] EIP is at iret_exc+0x4fd/0x75d [17179765.492000] eax: 00000000 ebx: 00000000 ecx: 2b646970 edx: 336e3094 [17179765.492000] esi: 0809c724 edi: 00000000 ebp: 00000003 esp: c32b3f34 [17179765.492000] ds: 007b es: 007b ss: 0068 [17179765.492000] Process so6-3-test (pid: 7227, threadinfo=c32b2000 task=c620e550) [17179765.492000] Stack: 00000000 2b646970 00000000 2b646970 d0833913 00000000 0809c724 2b646970 [17179765.492000] 0809c720 c47c8d40 40040c01 0809c720 c016a5f2 cadb0624 c47c8d40 40040c01 [17179765.492000] 0809c720 c47c8d40 00000000 c016a654 c015845a cffefa80 c47c8d40 c016a90d [17179765.492000] Call Trace: [17179765.492000] altpinfo_ioctl+0x103/0x170 [altpinfo] do_ioctl+0x52/0x60 [17179765.492000] vfs_ioctl+0x54/0x2b0 do_sys_open+0x9a/0xd0 [17179765.492000] sys_ioctl+0x5d/0x90 syscall_call+0x7/0xb [17179765.492000] Code: 5c 24 28 c7 03 f2 ff ff ff e9 12 be f0 ff ba f2 ff ff ff e9 6d c0 f0 ff 8d 0c 8a e9 8f c0 f0 ff 01 c1 eb 03 8d 0c 88 51 50 31 c0 aa 58 59 e9 ca c0 f0 ff 8d 0c 88 51 50 31 c0 f3 aa 58 59 e9 [17179765.492000] EIP: [] iret_exc+0x4fd/0x75d SS:ESP 0068:c32b3f34 [17179765.492000] <6>altpinfo: unloaded The function altpinfo_ioctl looks like this: static int altpinfo_ioctl(struct inode *inode, struct file *f, unsigned int cmd, unsigned long arg) { int ret = 0; switch (cmd) { case API_GET_FMT: ret = put_fmt((char __user *)arg); break; case API_SET_FMT: if (!capable(CAP_SYS_ADMIN)) { return -EPERM; } ret = get_fmt((char __user *)arg); break; case API_GET_CURLEN: ret = put_curlen(f, (int __user *)arg); break; default: ret = -ENOTTY; break; } return ret; } Helper functions look like this: static int put_curlen(struct file *f, int __user *arg) { int left; struct private_data *p = (struct private_data *) f->private_data; if (down_interruptible(&p->sem) != 0) { return -ERESTARTSYS; } left = p->buffer_size - f->f_pos; up(&p->sem); return put_user(left, arg); } static int put_fmt(char __user *arg) { char *fmt; int ret; ret = get_format_string(&fmt); if (ret != 0) { return ret; } if (copy_to_user(arg, fmt, strlen(fmt)) != 0) { return -EIO; } kfree(fmt); return 0; } /* Better make arg buffer at least 4 bytes alligned in userspace! */ static int get_fmt(char __user *arg) { int ret; int len; char *buf; ret = get_user(len, (int __user *)arg); if (ret != 0) { return ret; } buf = kcalloc(len, sizeof(char), GFP_KERNEL); if (copy_from_user(buf, arg + 4, len) != 0) { kfree(buf); return -EIO; } buf[len] = '\0'; ret = parse_format(buf); if (ret != 0) { kfree(buf); return ret; } return 0; } I wonder what does this oops mean and what that function iret_exc really does and why? It looks like some automagical exception handler but I am not sure about it. I can't reproduce this oops for now on my machine. Could anybody tell me why that code is wrong and why is this oops in iret_exc? (At the same time I am waiting for further info from the tester but I am not sure when and how much I will get.) Any help on tracing this down would be appreciated. Thanks, Grzegorz Kulewski