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Anoob Soman 79edd00dc6 scsi: libiscsi: Fix race between iscsi_xmit_task and iscsi_complete_task 
When a target sends Check Condition, whilst initiator is busy xmiting
re-queued data, could lead to race between iscsi_complete_task() and
iscsi_xmit_task() and eventually crashing with the following kernel
backtrace.

[3326150.987523] ALERT: BUG: unable to handle kernel NULL pointer dereference at 0000000000000078
[3326150.987549] ALERT: IP: [<ffffffffa05ce70d>] iscsi_xmit_task+0x2d/0xc0 [libiscsi]
[3326150.987571] WARN: PGD 569c8067 PUD 569c9067 PMD 0
[3326150.987582] WARN: Oops: 0002 [#1] SMP
[3326150.987593] WARN: Modules linked in: tun nfsv3 nfs fscache dm_round_robin
[3326150.987762] WARN: CPU: 2 PID: 8399 Comm: kworker/u32:1 Tainted: G O 4.4.0+2 #1
[3326150.987774] WARN: Hardware name: Dell Inc. PowerEdge R720/0W7JN5, BIOS 2.5.4 01/22/2016
[3326150.987790] WARN: Workqueue: iscsi_q_13 iscsi_xmitworker [libiscsi]
[3326150.987799] WARN: task: ffff8801d50f3800 ti: ffff8801f5458000 task.ti: ffff8801f5458000
[3326150.987810] WARN: RIP: e030:[<ffffffffa05ce70d>] [<ffffffffa05ce70d>] iscsi_xmit_task+0x2d/0xc0 [libiscsi]
[3326150.987825] WARN: RSP: e02b:ffff8801f545bdb0 EFLAGS: 00010246
[3326150.987831] WARN: RAX: 00000000ffffffc3 RBX: ffff880282d2ab20 RCX: ffff88026b6ac480
[3326150.987842] WARN: RDX: 0000000000000000 RSI: 00000000fffffe01 RDI: ffff880282d2ab20
[3326150.987852] WARN: RBP: ffff8801f545bdc8 R08: 0000000000000000 R09: 0000000000000008
[3326150.987862] WARN: R10: 0000000000000000 R11: 000000000000fe88 R12: 0000000000000000
[3326150.987872] WARN: R13: ffff880282d2abe8 R14: ffff880282d2abd8 R15: ffff880282d2ac08
[3326150.987890] WARN: FS: 00007f5a866b4840(0000) GS:ffff88028a640000(0000) knlGS:0000000000000000
[3326150.987900] WARN: CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033
[3326150.987907] WARN: CR2: 0000000000000078 CR3: 0000000070244000 CR4: 0000000000042660
[3326150.987918] WARN: Stack:
[3326150.987924] WARN: ffff880282d2ad58 ffff880282d2ab20 ffff880282d2abe8 ffff8801f545be18
[3326150.987938] WARN: ffffffffa05cea90 ffff880282d2abf8 ffff88026b59cc80 ffff88026b59cc00
[3326150.987951] WARN: ffff88022acf32c0 ffff880289491800 ffff880255a80800 0000000000000400
[3326150.987964] WARN: Call Trace:
[3326150.987975] WARN: [<ffffffffa05cea90>] iscsi_xmitworker+0x2f0/0x360 [libiscsi]
[3326150.987988] WARN: [<ffffffff8108862c>] process_one_work+0x1fc/0x3b0
[3326150.987997] WARN: [<ffffffff81088f95>] worker_thread+0x2a5/0x470
[3326150.988006] WARN: [<ffffffff8159cad8>] ? __schedule+0x648/0x870
[3326150.988015] WARN: [<ffffffff81088cf0>] ? rescuer_thread+0x300/0x300
[3326150.988023] WARN: [<ffffffff8108ddf5>] kthread+0xd5/0xe0
[3326150.988031] WARN: [<ffffffff8108dd20>] ? kthread_stop+0x110/0x110
[3326150.988040] WARN: [<ffffffff815a0bcf>] ret_from_fork+0x3f/0x70
[3326150.988048] WARN: [<ffffffff8108dd20>] ? kthread_stop+0x110/0x110
[3326150.988127] ALERT: RIP [<ffffffffa05ce70d>] iscsi_xmit_task+0x2d/0xc0 [libiscsi]
[3326150.988138] WARN: RSP <ffff8801f545bdb0>
[3326150.988144] WARN: CR2: 0000000000000078
[3326151.020366] WARN: ---[ end trace 1c60974d4678d81b ]---

Commit 6f8830f5bb ("scsi: libiscsi: add lock around task lists to fix
list corruption regression") introduced "taskqueuelock" to fix list
corruption during the race, but this wasn't enough.

Re-setting of conn->task to NULL, could race with iscsi_xmit_task().
iscsi_complete_task()
{
    ....
    if (conn->task == task)
        conn->task = NULL;
}

conn->task in iscsi_xmit_task() could be NULL and so will be task.
__iscsi_get_task(task) will crash (NullPtr de-ref), trying to access
refcount.

iscsi_xmit_task()
{
    struct iscsi_task *task = conn->task;

    __iscsi_get_task(task);
}

This commit will take extra conn->session->back_lock in iscsi_xmit_task()
to ensure iscsi_xmit_task() waits for iscsi_complete_task(), if
iscsi_complete_task() wins the race.  If iscsi_xmit_task() wins the race,
iscsi_xmit_task() increments task->refcount
(__iscsi_get_task) ensuring iscsi_complete_task() will not iscsi_free_task().

Signed-off-by: Anoob Soman <anoob.soman@citrix.com>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Acked-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
2019-02-15 22:05:04 -05:00
arch Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
block for-4.21/block-20190102 2019-01-02 18:49:58 -08:00
certs kbuild: remove redundant target cleaning on failure 2019-01-06 09:46:51 +09:00
crypto Kconfig updates for v4.21 2018-12-29 13:03:29 -08:00
Documentation Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
drivers scsi: libiscsi: Fix race between iscsi_xmit_task and iscsi_complete_task 2019-02-15 22:05:04 -05:00
firmware kbuild: change filechk to surround the given command with { } 2019-01-06 09:46:51 +09:00
fs Add Adiantum support for fscrypt 2019-01-06 12:21:11 -08:00
include Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
init jump_label: move 'asm goto' support test to Kconfig 2019-01-06 09:46:51 +09:00
ipc ipc: IPCMNI limit check for semmni 2018-10-31 08:54:14 -07:00
kernel Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
lib Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
LICENSES This is a fairly typical cycle for documentation. There's some welcome 2018-10-24 18:01:11 +01:00
mm Change mincore() to count "mapped" pages rather than "cached" pages 2019-01-06 13:43:02 -08:00
net jump_label: move 'asm goto' support test to Kconfig 2019-01-06 09:46:51 +09:00
samples Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid 2019-01-05 17:53:40 -08:00
scripts kconfig: rename generated .*conf-cfg to *conf-cfg 2019-01-06 10:47:09 +09:00
security Merge branch 'mount.part1' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-01-05 13:25:58 -08:00
sound Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
tools Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt Merge branch 'akpm' (patches from Andrew) 2019-01-05 09:16:18 -08:00
.clang-format page cache: Convert find_get_pages_contig to XArray 2018-10-21 10:46:34 -04:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support for DT binding schema checks 2018-12-13 09:41:32 -06:00
.mailmap A few early MIPS fixes for 4.21: 2019-01-05 12:48:25 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Add CREDITS entry for Shaohua Li 2019-01-04 14:27:09 -07:00
Kbuild kbuild: use assignment instead of define ... endef for filechk_* rules 2019-01-06 10:22:35 +09:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS chrome platform changes for v4.21 2019-01-06 11:40:06 -08:00
Makefile Linux 5.0-rc1 2019-01-06 17:08:20 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.