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    SubjectRe: [Bugme-new] [Bug 13850] New: reading /proc/kcore causes oops

    (switched to email. Please respond via emailed reply-to-all, not via the
    bugzilla web interface).

    On Mon, 27 Jul 2009 03:19:11 GMT
    bugzilla-daemon@bugzilla.kernel.org wrote:

    > http://bugzilla.kernel.org/show_bug.cgi?id=13850
    >
    > Summary: reading /proc/kcore causes oops
    > Product: Other
    > Version: 2.5
    > Kernel Version: 2.6.30
    > Platform: All
    > OS/Version: Linux
    > Tree: Mainline
    > Status: NEW
    > Severity: normal
    > Priority: P1
    > Component: Other
    > AssignedTo: other_other@kernel-bugs.osdl.org
    > ReportedBy: scgtrp@gmail.com
    > Regression: No
    >
    >
    > When trying to use an old trick for finding lost data by grep'ing /proc/kcore,
    > I managed to oops my server's kernel. I tried again on my desktop with cat
    > /proc/kcore >/dev/null. cat was killed, and a similar oops appeared in my dmesg
    > which I managed to capture:
    >
    > Jul 26 23:04:13 mike kernel: BUG: unable to handle kernel paging request at
    > e07cf000
    > Jul 26 23:04:13 mike kernel: IP: [<c0224dd1>] read_kcore+0x2c1/0x4b0
    > Jul 26 23:04:13 mike kernel: *pde = 1b5f4067 *pte = 00000000
    > Jul 26 23:04:13 mike kernel: Oops: 0000 [#2] PREEMPT SMP
    > Jul 26 23:04:13 mike kernel: last sysfs file: /sys/power/state
    > Jul 26 23:04:13 mike kernel: Modules linked in: ipv6 sg sd_mod fuse usb_storage
    > usbhid hid snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device
    > snd_pcm_oss snd_mixer_oss ppdev snd_intel8x0 snd_ac97_codec ac97_bus snd_pcm
    > snd_timer ohci_hcd parport_pc lp parport snd soundcore snd_page_alloc nvidia(P)
    > agpgart k8temp ehci_hcd forcedeth i2c_nforce2 i2c_core usbcore evdev thermal
    > processor fan button battery ac rtc_cmos rtc_core rtc_lib ext3 jbd mbcache
    > ide_gd_mod ide_cd_mod cdrom sata_nv libata amd74xx ide_pci_generic ide_core
    > scsi_mod
    > Jul 26 23:04:13 mike kernel:
    > Jul 26 23:04:13 mike kernel: Pid: 4835, comm: cat Tainted: P D
    > (2.6.30-ARCH #1) W3107
    > Jul 26 23:04:13 mike kernel: EIP: 0060:[<c0224dd1>] EFLAGS: 00210286 CPU: 0
    > Jul 26 23:04:13 mike kernel: EIP is at read_kcore+0x2c1/0x4b0
    > Jul 26 23:04:13 mike kernel: EAX: ddb71ac0 EBX: 00001000 ECX: 00000400 EDX:
    > e07d0000
    > Jul 26 23:04:13 mike kernel: ESI: e07cf000 EDI: da20e000 EBP: d73fbf30 ESP:
    > d73fbefc
    > Jul 26 23:04:13 mike kernel: DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
    > Jul 26 23:04:13 mike kernel: Process cat (pid: 4835, ti=d73fa000 task=d4b5cc00
    > task.ti=d73fa000)
    > Jul 26 23:04:13 mike kernel: Stack:
    > Jul 26 23:04:13 mike kernel: da20e000 e07cf000 d73fbf90 00000000 09459000
    > 00000000 00008000 00001000
    > Jul 26 23:04:13 mike kernel: 00000000 6798ed89 ddaf0000 ce920c80 c0224b10
    > fffffffb c0219e89 d73fbf90
    > Jul 26 23:04:13 mike kernel: 09459000 00008000 d73fbf90 6798ed89 ce920c80
    > 00008000 09459000 d73fbf80
    > Jul 26 23:04:13 mike kernel: Call Trace:
    > Jul 26 23:04:13 mike kernel: [<c0224b10>] ? read_kcore+0x0/0x4b0
    > Jul 26 23:04:13 mike kernel: [<c0219e89>] ? proc_reg_read+0x79/0xc0
    > Jul 26 23:04:13 mike kernel: [<c01d1b43>] ? vfs_read+0xc3/0x1a0
    > Jul 26 23:04:13 mike kernel: [<c0219e10>] ? proc_reg_read+0x0/0xc0
    > Jul 26 23:04:13 mike kernel: [<c01d1d28>] ? sys_read+0x58/0xb0
    > Jul 26 23:04:13 mike kernel: [<c0103c73>] ? sysenter_do_call+0x12/0x28
    > Jul 26 23:04:13 mike kernel: Code: 89 fb 0f 43 f2 89 ca 29 f2 29 f3 39 f9 0f 46
    > da 29 5c 24 14 f6 40 0c 01 8d 14 33 75 19 89 d9 89 f7 c1 e9 02 2b 7c 24 04 03
    > 3c 24 <f3> a5 89 d9 83 e1 03 74 02 f3 a4 8b 4c 24 14 8b 00 85 c9 74 0a
    > Jul 26 23:04:13 mike kernel: EIP: [<c0224dd1>] read_kcore+0x2c1/0x4b0 SS:ESP
    > 0068:d73fbefc
    > Jul 26 23:04:13 mike kernel: CR2: 00000000e07cf000
    > Jul 26 23:04:13 mike kernel: ---[ end trace 3bb140bf57c1987e ]---
    > Jul 26 23:04:13 mike kernel: note: cat[4835] exited with preempt_count 1
    >
    > I understand it's quite a ridiculous thing to do, but userspace shouldn't be
    > able to cause kernel errors, no matter what kind of insane things I try.
    >

    gee, read_kcore() is huge. This makes it pretty hard to work out where
    exactly the kernel died.

    Is it reproducible, or do you still have the vmlinux from the above
    oops on-disk?

    If so, can you please help work out where it crashed? You could run
    something like

    addr2line -e vmlinux 0xc0224dd1

    or

    gdb vmlinux
    (gdb) l *0xc0224dd1

    both of these will need CONFIG_DEBUG_INFO=y.


    It is possible to work out where the kernel crashed using the above
    Code: line, but it's a bit of a pain.

    Thanks.



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