Message-ID: <BANLkTim8=Tf62gfTePczL11K_tYm71NXwg@mail.gmail.com>
Date:	Mon, 18 Apr 2011 08:53:54 +0200
From:	Robert Święcki <robert@...ecki.net>
To:	linux-kernel@...r.kernel.org
Subject: Re: Kernel panic (NULL ptr deref?) in find_ge_pid()/next_pidmap()
 (via sys_getdents or sys_readdir)

On Wed, Apr 13, 2011 at 11:12 PM, Robert Święcki <robert@...ecki.net> wrote:
> Oops: (kdb's dumpall attached)
>
> [18608.476700] general protection fault: 0000 [#1] PREEMPT SMP
> [18608.476704] last sysfs file:
> /sys/devices/platform/microcode/power/runtime_status
> [18608.477002] CPU 0
> [18608.477002] Pid: 31157, comm: iknowthis Not tainted 2.6.39-rc3 #4
> Dell Inc.                 Precision WorkStation 390    /0GH911
> [18608.477002] RIP: 0010:[<ffffffff810ac3cc>]  [<ffffffff810ac3cc>]
> next_pidmap+0x38/0x7f
> [18608.477002] RSP: 0000:ffff88007b40fd48  EFLAGS: 00010203
> [18608.477002] RAX: 0000000000000000 RBX: 001fffff82753988 RCX: 0000000000000034
> [18608.477002] RDX: 0000000000003b6e RSI: 001ffffffff2c980 RDI: ffffffff82827000
> [18608.477002] RBP: ffff88007b40fd68 R08: a000000000000000 R09: 5b68000000000000
> [18608.477002] R10: ffff88007b40e000 R11: ffff88007b40fdb8 R12: ffffffff82827000
> [18608.477002] R13: ffffffff82827808 R14: ffffffff81199146 R15: ffffffff81199146
> [18608.477002] FS:  0000000000000000(0000) GS:ffff88012bc00000(0063)
> knlGS:00000000f75406c0
> [18608.477002] CS:  0010 DS: 002b ES: 002b CR0: 000000008005003b
> [18608.477002] CR2: 000000000809601c CR3: 0000000118457000 CR4: 00000000000006f0
> [18608.477002] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [18608.477002] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [18608.477002] Process iknowthis (pid: 31157, threadinfo
> ffff88007b40e000, task ffff880124f6c560)
> [18608.477002] Stack:
> [18608.477002]  ffff88011e2e5c80 00000000964c3b6d 0000000000000000
> ffffffff82827000
> [18608.477002]  ffff88007b40fd98 ffffffff810ac446 ffff88011e2e5c80
> ffffffff82827000
> [18608.477002]  00000000964c3b6d ffff880124f68000 ffff88007b40fdf8
> ffffffff811aedbb
> [18608.477002] Call Trace:
> [18608.477002]  [<ffffffff810ac446>] find_ge_pid+0x33/0x45
> [18608.477002]  [<ffffffff811aedbb>] next_tgid+0x3c/0x93
> [18608.477002]  [<ffffffff81199146>] ? compat_sys_io_getevents+0xae/0xae
> [18608.477002]  [<ffffffff810abf69>] ? get_pid_task+0x49/0x51
> [18608.477002]  [<ffffffff811aef6f>] proc_pid_readdir+0x15d/0x1b0
> [18608.477002]  [<ffffffff81199146>] ? compat_sys_io_getevents+0xae/0xae
> [18608.477002]  [<ffffffff81199146>] ? compat_sys_io_getevents+0xae/0xae
> [18608.477002]  [<ffffffff81199146>] ? compat_sys_io_getevents+0xae/0xae
> [18608.477002]  [<ffffffff811ab262>] proc_root_readdir+0x43/0x4b
> [18608.477002]  [<ffffffff8116bd57>] vfs_readdir+0x71/0xae
> [18608.477002]  [<ffffffff81197d18>] compat_sys_getdents+0x81/0xcc
> [18608.477002]  [<ffffffff81f26703>] ia32_do_call+0x13/0x13
> [18608.477002] Code: 0f 1f 44 00 00 ff c6 49 89 fc 89 f2 4c 8d af 08
> 08 00 00 48 63 f6 81 e2 ff 7f 00 00 48 c1 ee 0f 48 c1 e6 04 48 8d 5c
> 37 08 eb 36
> [18608.477002]  8b 7b 08 48 85 ff 74 27 48 63 d2 be 00 80 00 00 e8 66 ab 3e
> [18608.477002] RIP  [<ffffffff810ac3cc>] next_pidmap+0x38/0x7f
> [18608.477002]  RSP <ffff88007b40fd48>
> [18626.313012] ---[ end trace 947a53151707da51 ]---

And a quick kgdb session:

(gdb) target remote /dev/ttyS0
Remote debugging using /dev/ttyS0
next_pidmap (pid_ns=0xffffffff82827000, last=<value optimized out>) at
kernel/pid.c:229
229                     if (unlikely(!map->page))

(gdb) p map
$1 = (struct pidmap *) 0x1fffff82745c68
(gdb) p map->page
Cannot access memory at address 0x1fffff82745c70

(gdb) bt
#0  next_pidmap (pid_ns=0xffffffff82827000, last=<value optimized
out>) at kernel/pid.c:229
#1  0xffffffff810ac446 in find_ge_pid (nr=-1889315394,
ns=0xffffffff82827000) at kernel/pid.c:527
#2  0xffffffff811aedbb in next_tgid (ns=0xffffffff82827000, iter=...)
at fs/proc/base.c:3087
#3  0xffffffff811aef6f in proc_pid_readdir (filp=0xffff880020155840,
dirent=<value optimized out>, filldir=0xffffffff811992c0
<compat_fillonedir>) at fs/proc/base.c:3146
#4  0xffffffff811ab262 in proc_root_readdir (filp=0xffff880020155840,
dirent=0xffff8800c82d1f48, filldir=0xffffffff811992c0
<compat_fillonedir>) at fs/proc/root.c:159
#5  0xffffffff8116bd57 in vfs_readdir (file=0xffff880020155840,
filler=0xffffffff811992c0 <compat_fillonedir>, buf=0xffff8800c82d1f48)
at fs/readdir.c:40
#6  0xffffffff81197da9 in compat_sys_old_readdir (fd=<value optimized
out>, dirent=0xf777a000, count=<value optimized out>) at
fs/compat.c:901
#7  <signal handler called>
#8  0x00000000080658d2 in ?? ()
Cannot access memory at address 0x29d58137

(gdb) up
#1  0xffffffff810ac446 in find_ge_pid (nr=-1889315394,
ns=0xffffffff82827000) at kernel/pid.c:527
527                     nr = next_pidmap(ns, nr);

(gdb) p nr
$5 = -1889315394

(gdb) up
#2  0xffffffff811aedbb in next_tgid (ns=0xffffffff82827000, iter=...)
at fs/proc/base.c:3087
3087            pid = find_ge_pid(iter.tgid, ns);

(gdb) p iter
$8 = {tgid = 2405651902, task = 0x0}

Might it be unsigned (2405651902) vs signed (-1889315394) problem? The
map is counted as

map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];

so




-- 
Robert Święcki
--
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