2018-01-03 08:21:25 +01:00
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From a79cb4d4e540c72a601ca0494e914565c16e2893 Mon Sep 17 00:00:00 2001
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Message-Id: <a79cb4d4e540c72a601ca0494e914565c16e2893.1514959852.git.jan.steffens@gmail.com>
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In-Reply-To: <fb89d912d5f7289d3a922c77b671e36e1c740f5e.1514959852.git.jan.steffens@gmail.com>
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References: <fb89d912d5f7289d3a922c77b671e36e1c740f5e.1514959852.git.jan.steffens@gmail.com>
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2017-12-26 01:24:55 +01:00
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From: Tejun Heo <tj@kernel.org>
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Date: Wed, 20 Dec 2017 07:09:19 -0800
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2018-01-03 08:21:25 +01:00
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Subject: [PATCH 6/7] cgroup: fix css_task_iter crash on CSS_TASK_ITER_PROC
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2017-12-26 01:24:55 +01:00
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While teaching css_task_iter to handle skipping over tasks which
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aren't group leaders, bc2fb7ed089f ("cgroup: add @flags to
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css_task_iter_start() and implement CSS_TASK_ITER_PROCS") introduced a
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silly bug.
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CSS_TASK_ITER_PROCS is implemented by repeating
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css_task_iter_advance() while the advanced cursor is pointing to a
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non-leader thread. However, the cursor variable, @l, wasn't updated
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when the iteration has to advance to the next css_set and the
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following repetition would operate on the terminal @l from the
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previous iteration which isn't pointing to a valid task leading to
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oopses like the following or infinite looping.
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BUG: unable to handle kernel NULL pointer dereference at 0000000000000254
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IP: __task_pid_nr_ns+0xc7/0xf0
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PGD 0 P4D 0
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Oops: 0000 [#1] SMP
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...
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CPU: 2 PID: 1 Comm: systemd Not tainted 4.14.4-200.fc26.x86_64 #1
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Hardware name: System manufacturer System Product Name/PRIME B350M-A, BIOS 3203 11/09/2017
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task: ffff88c4baee8000 task.stack: ffff96d5c3158000
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RIP: 0010:__task_pid_nr_ns+0xc7/0xf0
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RSP: 0018:ffff96d5c315bd50 EFLAGS: 00010206
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RAX: 0000000000000000 RBX: ffff88c4b68c6000 RCX: 0000000000000250
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RDX: ffffffffa5e47960 RSI: 0000000000000000 RDI: ffff88c490f6ab00
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RBP: ffff96d5c315bd50 R08: 0000000000001000 R09: 0000000000000005
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R10: ffff88c4be006b80 R11: ffff88c42f1b8004 R12: ffff96d5c315bf18
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R13: ffff88c42d7dd200 R14: ffff88c490f6a510 R15: ffff88c4b68c6000
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FS: 00007f9446f8ea00(0000) GS:ffff88c4be680000(0000) knlGS:0000000000000000
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CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
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CR2: 0000000000000254 CR3: 00000007f956f000 CR4: 00000000003406e0
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Call Trace:
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cgroup_procs_show+0x19/0x30
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cgroup_seqfile_show+0x4c/0xb0
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kernfs_seq_show+0x21/0x30
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seq_read+0x2ec/0x3f0
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kernfs_fop_read+0x134/0x180
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__vfs_read+0x37/0x160
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? security_file_permission+0x9b/0xc0
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vfs_read+0x8e/0x130
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SyS_read+0x55/0xc0
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entry_SYSCALL_64_fastpath+0x1a/0xa5
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RIP: 0033:0x7f94455f942d
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RSP: 002b:00007ffe81ba2d00 EFLAGS: 00000293 ORIG_RAX: 0000000000000000
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RAX: ffffffffffffffda RBX: 00005574e2233f00 RCX: 00007f94455f942d
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RDX: 0000000000001000 RSI: 00005574e2321a90 RDI: 000000000000002b
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RBP: 0000000000000000 R08: 00005574e2321a90 R09: 00005574e231de60
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R10: 00007f94458c8b38 R11: 0000000000000293 R12: 00007f94458c8ae0
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R13: 00007ffe81ba3800 R14: 0000000000000000 R15: 00005574e2116560
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Code: 04 74 0e 89 f6 48 8d 04 76 48 8d 04 c5 f0 05 00 00 48 8b bf b8 05 00 00 48 01 c7 31 c0 48 8b 0f 48 85 c9 74 18 8b b2 30 08 00 00 <3b> 71 04 77 0d 48 c1 e6 05 48 01 f1 48 3b 51 38 74 09 5d c3 8b
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RIP: __task_pid_nr_ns+0xc7/0xf0 RSP: ffff96d5c315bd50
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Fix it by moving the initialization of the cursor below the repeat
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label. While at it, rename it to @next for readability.
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Signed-off-by: Tejun Heo <tj@kernel.org>
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Fixes: bc2fb7ed089f ("cgroup: add @flags to css_task_iter_start() and implement CSS_TASK_ITER_PROCS")
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Cc: stable@vger.kernel.org # v4.14+
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Reported-by: Laura Abbott <labbott@redhat.com>
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Reported-by: Bronek Kozicki <brok@incorrekt.com>
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Reported-by: George Amanakis <gamanakis@gmail.com>
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Signed-off-by: Tejun Heo <tj@kernel.org>
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---
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kernel/cgroup/cgroup.c | 14 ++++++--------
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1 file changed, 6 insertions(+), 8 deletions(-)
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diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
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index 44857278eb8aa6a2..030e4286f14c715e 100644
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--- a/kernel/cgroup/cgroup.c
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+++ b/kernel/cgroup/cgroup.c
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@@ -4059,26 +4059,24 @@ static void css_task_iter_advance_css_set(struct css_task_iter *it)
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static void css_task_iter_advance(struct css_task_iter *it)
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{
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- struct list_head *l = it->task_pos;
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+ struct list_head *next;
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lockdep_assert_held(&css_set_lock);
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- WARN_ON_ONCE(!l);
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-
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repeat:
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/*
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* Advance iterator to find next entry. cset->tasks is consumed
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* first and then ->mg_tasks. After ->mg_tasks, we move onto the
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* next cset.
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*/
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- l = l->next;
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+ next = it->task_pos->next;
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- if (l == it->tasks_head)
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- l = it->mg_tasks_head->next;
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+ if (next == it->tasks_head)
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+ next = it->mg_tasks_head->next;
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- if (l == it->mg_tasks_head)
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+ if (next == it->mg_tasks_head)
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css_task_iter_advance_css_set(it);
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else
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- it->task_pos = l;
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+ it->task_pos = next;
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/* if PROCS, skip over tasks which aren't group leaders */
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if ((it->flags & CSS_TASK_ITER_PROCS) && it->task_pos &&
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--
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2.15.1
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