From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: [BUG] mmotm-081130: null pointer deref in sigkill_pending() From: Lee Schermerhorn Content-Type: text/plain Date: Tue, 02 Dec 2008 08:18:53 -0500 Message-Id: <1228223933.30995.28.camel@lts-notebook> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: linux-kernel , Andrew Morton Cc: Ying Han , linux-mm , Hugh Dickins List-ID: While testing mmotm [11/29, 11/30, likely in 12/01], I came across the following bug after ~2 hours of heavy stress on x86_64 [same bug/trace hit on ia64]: BUG: unable to handle kernel NULL pointer dereference at 0000000000000038 IP: [] sigkill_pending+0x19/0x30 PGD 63be12067 PUD 7fd0cc067 PMD 0 Oops: 0000 [#1] SMP DEBUG_PAGEALLOC last sysfs file: /sys/block/hda/removable CPU 7 Modules linked in: sunrpc ipv6 dm_mirror dm_region_hash dm_log dm_mod rfkill input_polldev pci_slot parport_pc lp parport ide_cd_mod cdrom serio_raw hpilo hpwdt button amd_rng pata_acpi i2c_amd756 libata i2c_core pcspkr mptspi mptscsih sym53c8xx scsi_transport_spi sd_mod scsi_mod mptbase ext3 jbd ehci_hcd ohci_hcd uhci_hcd Pid: 19530, comm: ps Not tainted 2.6.28-rc6-mmotm-081130-2235 #10 RIP: 0010:[] [] sigkill_pending+0x19/0x30 RSP: 0018:ffff8806a64efd38 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 000000000000000e RCX: ffff8805fc96fb00 RDX: ffff8806a64efe38 RSI: 00007fff62423000 RDI: ffff88020c87abe0 RBP: ffff8806a64efd38 R08: 0000000000000000 R09: ffff8806a64efe30 R10: 0000000000000002 R11: 0000000000000000 R12: ffff8805fc96fb00 R13: 0000000000000000 R14: 0000000000000010 R15: ffff8806a64efe30 FS: 00007f32d4ac46f0(0000) GS:ffff8807fed46d80(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 0000000000000038 CR3: 0000000784571000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process ps (pid: 19530, threadinfo ffff8806a64ee000, task ffff88062cf6d7c0) Stack: ffff8806a64efdb8 ffffffff80298986 0000000000000001 ffff88062cf6d7c0 ffff8803ad100680 ffff88020c87abe0 0000000000000000 ffff8806a64efe38 ffff8806a64efe30 00000001804f0765 00007fff624236be 0000000000000000 Call Trace: [] __get_user_pages+0x166/0x440 [] get_user_pages+0x32/0x40 [] access_process_vm+0x10b/0x1e0 [] proc_pid_cmdline+0x90/0x120 [] ? alloc_pages_current+0xa8/0x100 [] proc_info_read+0x9b/0xe0 [] vfs_read+0xc4/0x160 [] sys_read+0x50/0x90 [] system_call_fastpath+0x16/0x1b Code: e8 08 83 e0 01 c3 66 0f 1f 44 00 00 66 0f 1f 44 00 00 f6 87 49 05 00 00 01 55 b8 01 00 00 00 48 89 e5 75 12 48 8b 87 10 05 00 00 <48> 8b 40 38 48 c1 e8 08 83 e0 01 c9 c3 66 2e 0f 1f 84 00 00 00 RIP [] sigkill_pending+0x19/0x30 RSP CR2: 0000000000000038 ---[ end trace 80efa2c8bcce4fdc ]--- Ad hoc instrumentation showed that this is likely the result of the "make-get_user_pages-interruptible" patch in mmotm. The test workload includes a number of tasks that repeatedly run a list of miscellaneous programs, including ps(1). Occasionally, ps will catch a task with a NULL "tsk->signal" [exiting?], resulting in a null pointer deref in sigkill_pending() called from __get_user_pages(). Before the aforementioned patch, sigkill_pending() was only called from ptrace_stop() for tsk == current. The comment block on ptrace_stop() says: "This must be called with current->sighand->siglock held." So, it doesn't look safe to call sigkill_pending() from __get_user_pages()--especially on a task != current--without similar locking. I'm not sure what the correct fix should be here. Related: the patch and it's update add the following to __get_user_pages(): if (unlikely(sigkill_pending(current) || sigkill_pending(tsk))) return i ? i : -ERESTARTSYS; As a minimum, I don't think we want to call the second sigkill_pending() unless tsk != current. Lee -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org