On 29.06.2021 12:33, Pavel Tikhomirov wrote:
On 25.06.2021 20:12, Andrey Zhadchenko wrote:
ve_ns is not guaranteed to be non-NULL. Fix
is_sb_ve_accessible() and sync_collect_filesystems()
Also add rcu_dereference since ve->ve_ns is rcu-protected
An example of shell commands to crash kernel:
mkdir /sys/fs/cgroup/ve/10001
cat /sys/fs/cgroup/ve/10001/tasks
echo 10001 > /sys/fs/cgroup/ve/10001/ve.veid
echo $$ > /sys/fs/cgroup/ve/10001/tasks
sync
[59390.889322] BUG: unable to handle kernel NULL pointer dereference
at 0000000000000018
[59390.889395] PGD 0 P4D 0
[59390.889442] Oops: 0000 [#1] SMP PTI
[59390.889492] CPU: 1 PID: 8950 Comm: sync ve: 10001 Kdump: loaded Not
tainted 4.18.0-240.1.1.vz8.5.47 #1 5.47
[59390.889554] Hardware name: Virtuozzo KVM, BIOS 1.10.2-3.1.vz7.3
04/01/2014
[59390.889622] RIP: 0010:sync_filesystems_ve+0x34/0x220
[59390.889673] Code: 55 41 54 55 53 48 83 ec 20 65 48 8b 04 25 28 00
00 00 48 89 44 24 18 31 c0 48 8b 87 98 01 00 00 48 8d 6c 24 08 48 89
6c 24 08 <4c> 8b 68 18 48 8b 44 24 08 48 89 6c 24 10 48 39 c5 0f 85 ce
01 00
[59390.889798] RSP: 0018:ffffb1b7810a7ec0 EFLAGS: 00010246
[59390.889849] RAX: 0000000000000000 RBX: ffff92309ab7c418 RCX:
0000000000000000
[59390.889903] RDX: ffff92308bbff180 RSI: 0000000000000000 RDI:
ffff92309ab7c418
[59390.889958] RBP: ffffb1b7810a7ec8 R08: 0000000000000000 R09:
0000000000000000
[59390.890016] R10: 0000000000000000 R11: 0000000000000000 R12:
0000000000000000
[59390.890071] R13: 0000000000000000 R14: 0000000000000000 R15:
0000000000000000
[59390.890126] FS: 00007fd7880b6540(0000) GS:ffff9230bbb00000(0000)
knlGS:0000000000000000
[59390.890184] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[59390.890235] CR2: 0000000000000018 CR3: 000000010b22e000 CR4:
00000000000006e0
[59390.890293] Call Trace:
[59390.890351] ? __do_page_fault+0x23a/0x4f0
[59390.890407] ksys_sync+0x10d/0x130
[59390.890456] __ia32_sys_sync+0xa/0x10
[59390.890509] do_syscall_64+0x5b/0x1a0
[59390.890562] entry_SYSCALL_64_after_hwframe+0x65/0xca
[59390.890620] RIP: 0033:0x7fd787fe4ffb
[59390.890667] Code: c3 48 8b 0d a7 8e 0c 00 f7 d8 64 89 01 b8 ff ff
ff ff eb c2 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 a2 00 00
00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 75 8e 0c 00 f7 d8 64 89
01 48
[59390.890791] RSP: 002b:00007ffd853dd328 EFLAGS: 00000246 ORIG_RAX:
00000000000000a2
[59390.890848] RAX: ffffffffffffffda RBX: 00007ffd853dd468 RCX:
00007fd787fe4ffb
[59390.890903] RDX: 00007fd7880b2001 RSI: 0000000000000000 RDI:
00007fd788079b5e
[59390.890957] RBP: 0000000000000001 R08: 0000000000000000 R09:
0000000000000000
[59390.891012] R10: 0000000000000000 R11: 0000000000000246 R12:
0000000000000000
[59390.891067] R13: 0000000000000000 R14: 0000000000000000 R15:
00007fd7880ae1b4
[59390.896038] CR2: 0000000000000018
https://jira.sw.ru/browse/PSBM-130894
Signed-off-by: Andrey Zhadchenko <[email protected]>
---
fs/sync.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/fs/sync.c b/fs/sync.c
index ef4b1d1..2a7c96b 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -127,10 +127,20 @@ static int sync_filesystem_collected(struct
list_head *sync_list, struct super_b
static int sync_collect_filesystems(struct ve_struct *ve, struct
list_head *sync_list)
{
struct mount *mnt;
- struct mnt_namespace *mnt_ns = ve->ve_ns->mnt_ns;
+ struct mnt_namespace *mnt_ns;
+ struct nsproxy *ve_ns;
struct sync_sb *ss;
int ret = 0;
+ rcu_read_lock();
+ ve_ns = rcu_dereference(ve->ve_ns);
Above you read ve->ve_ns to ve_ns variable but never use it. You
probably designed it to use in the below code, because ve->ve_ns can
change to NULL after the check below and we still get crash.
+ if (!ve->ve_ns) {
+ rcu_read_unlock();
+ return 0;
+ }
+ mnt_ns = ve->ve_ns->mnt_ns;
One more thing, should not we get some refference on mnt_ns? Can not it
be released/freed by put_nsproxy() on ve_ns?
+ rcu_read_unlock();
+
BUG_ON(!list_empty(sync_list));
down_read(&namespace_sem);
@@ -185,9 +195,19 @@ static void sync_filesystems_ve(struct ve_struct
*ve, int wait)
static int is_sb_ve_accessible(struct ve_struct *ve, struct
super_block *sb)
{
struct mount *mnt;
- struct mnt_namespace *mnt_ns = ve->ve_ns->mnt_ns;
+ struct mnt_namespace *mnt_ns;
+ struct nsproxy *ve_ns;
int ret = 0;
+ rcu_read_lock();
+ ve_ns = rcu_dereference(ve->ve_ns);
Same thing here.
+ if (!ve->ve_ns) {
+ rcu_read_unlock();
+ return 0;
+ }
+ mnt_ns = ve->ve_ns->mnt_ns;
+ rcu_read_unlock();
+
down_read(&namespace_sem);
list_for_each_entry(mnt, &mnt_ns->list, mnt_list) {
if (mnt->mnt.mnt_sb == sb) {
--
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.
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