Connect and disconnect a nbd device repeatedly, will cause
NULL pointer fault.
It will appear by the steps:
1. Connect the nbd device and disconnect it, but now nbd device
is not disconnected totally.
2. Connect the same nbd device again immediately, it will fail
in nbd_start_device with a EBUSY return value.
3. Wait a second to make sure the last config_refs is reduced
and run nbd_config_put to disconnect the nbd device totally.
4. Start another process to open the nbd_device, config_refs
will increase and at the same time disconnect it.
To fix it, add a NBD_HAS_STARTED flag. Set it in nbd_start_device_ioctl
and nbd_genl_connect if nbd device is started successfully.
Clear it in nbd_config_put. Test it in nbd_genl_disconnect and
nbd_genl_reconfigure.
Signed-off-by: Sun Ke <[email protected]>
---
drivers/block/nbd.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index b4607dd96185..ddd364e208ab 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -83,6 +83,7 @@ struct link_dead_args {
#define NBD_DESTROY_ON_DISCONNECT 0
#define NBD_DISCONNECT_REQUESTED 1
+#define NBD_HAS_STARTED 2
struct nbd_config {
u32 flags;
@@ -1215,6 +1216,7 @@ static void nbd_config_put(struct nbd_device *nbd)
nbd->disk->queue->limits.discard_alignment = 0;
blk_queue_max_discard_sectors(nbd->disk->queue, UINT_MAX);
blk_queue_flag_clear(QUEUE_FLAG_DISCARD, nbd->disk->queue);
+ clear_bit(NBD_HAS_STARTED, &nbd->flags);
mutex_unlock(&nbd->config_lock);
nbd_put(nbd);
@@ -1290,6 +1292,8 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *b
ret = nbd_start_device(nbd);
if (ret)
return ret;
+ else
+ set_bit(NBD_HAS_STARTED, &nbd->flags);
if (max_part)
bdev->bd_invalidated = 1;
@@ -1961,6 +1965,7 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
mutex_unlock(&nbd->config_lock);
if (!ret) {
set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
+ set_bit(NBD_HAS_STARTED, &nbd->flags);
refcount_inc(&nbd->config_refs);
nbd_connect_reply(info, nbd->index);
}
@@ -2008,6 +2013,14 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
index);
return -EINVAL;
}
+
+ if (!test_bit(NBD_HAS_STARTED, &nbd->flags)) {
+ mutex_unlock(&nbd_index_mutex);
+ printk(KERN_ERR "nbd: device at index %d failed to start\n",
+ index);
+ return -EBUSY;
+ }
+
if (!refcount_inc_not_zero(&nbd->refs)) {
mutex_unlock(&nbd_index_mutex);
printk(KERN_ERR "nbd: device at index %d is going down\n",
@@ -2049,6 +2062,14 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
index);
return -EINVAL;
}
+
+ if (!test_bit(NBD_HAS_STARTED, &nbd->flags)) {
+ mutex_unlock(&nbd_index_mutex);
+ printk(KERN_ERR "nbd: device at index %d failed to start\n",
+ index);
+ return -EBUSY;
+ }
+
if (!refcount_inc_not_zero(&nbd->refs)) {
mutex_unlock(&nbd_index_mutex);
printk(KERN_ERR "nbd: device at index %d is going down\n",
--
2.17.2
On 1/17/20 6:50 AM, Sun Ke wrote:
> Connect and disconnect a nbd device repeatedly, will cause
> NULL pointer fault.
>
> It will appear by the steps:
> 1. Connect the nbd device and disconnect it, but now nbd device
> is not disconnected totally.
> 2. Connect the same nbd device again immediately, it will fail
> in nbd_start_device with a EBUSY return value.
> 3. Wait a second to make sure the last config_refs is reduced
> and run nbd_config_put to disconnect the nbd device totally.
> 4. Start another process to open the nbd_device, config_refs
> will increase and at the same time disconnect it.
>
> To fix it, add a NBD_HAS_STARTED flag. Set it in nbd_start_device_ioctl
> and nbd_genl_connect if nbd device is started successfully.
> Clear it in nbd_config_put. Test it in nbd_genl_disconnect and
> nbd_genl_reconfigure.
I don't doubt what you are seeing, but what exactly are we NULL pointer
dereferencing? I can't quite figure it out from the steps.
>
> Signed-off-by: Sun Ke <[email protected]>
> ---
> drivers/block/nbd.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index b4607dd96185..ddd364e208ab 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -83,6 +83,7 @@ struct link_dead_args {
>
> #define NBD_DESTROY_ON_DISCONNECT 0
> #define NBD_DISCONNECT_REQUESTED 1
> +#define NBD_HAS_STARTED 2
>
> struct nbd_config {
> u32 flags;
> @@ -1215,6 +1216,7 @@ static void nbd_config_put(struct nbd_device *nbd)
> nbd->disk->queue->limits.discard_alignment = 0;
> blk_queue_max_discard_sectors(nbd->disk->queue, UINT_MAX);
> blk_queue_flag_clear(QUEUE_FLAG_DISCARD, nbd->disk->queue);
> + clear_bit(NBD_HAS_STARTED, &nbd->flags);
>
> mutex_unlock(&nbd->config_lock);
> nbd_put(nbd);
> @@ -1290,6 +1292,8 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *b
> ret = nbd_start_device(nbd);
> if (ret)
> return ret;
> + else
> + set_bit(NBD_HAS_STARTED, &nbd->flags);
The else is superfluous here. Thanks,
Josef
On 01/17/2020 05:50 AM, Sun Ke wrote:
> Connect and disconnect a nbd device repeatedly, will cause
> NULL pointer fault.
>
> It will appear by the steps:
> 1. Connect the nbd device and disconnect it, but now nbd device
> is not disconnected totally.
> 2. Connect the same nbd device again immediately, it will fail
> in nbd_start_device with a EBUSY return value.
> 3. Wait a second to make sure the last config_refs is reduced
> and run nbd_config_put to disconnect the nbd device totally.
> 4. Start another process to open the nbd_device, config_refs
> will increase and at the same time disconnect it.
Just to make sure I understood this, for step 4 the process is doing:
open(/dev/nbdX);
ioctl(NBD_DISCONNECT, /dev/nbdX) or nbd_genl_disconnect(for /dev/nbdX)
?
There is no successful NBD_DO_IT / nbd_genl_connect between the open and
disconnect calls at step #4, because it would normally be done at #2 and
that failed. nbd_disconnect_and_put could then reference a null
recv_workq. If we are also racing with a close() then that could free
the device/config from under nbd_disconnect_and_put.
>
> To fix it, add a NBD_HAS_STARTED flag. Set it in nbd_start_device_ioctl
I'm not sure if we need the new bit. We could just add a check for a non
null task_recv in nbd_genl_disconnect like how nbd_start_device and
nbd_genl_disconnect do.
The new bit might be more clear which is nice. If we got this route,
should the new bit be a runtime_flag like other device state bits?
> and nbd_genl_connect if nbd device is started successfully.
> Clear it in nbd_config_put. Test it in nbd_genl_disconnect and
> nbd_genl_reconfigure.
>
> Signed-off-by: Sun Ke <[email protected]>
> ---
> drivers/block/nbd.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index b4607dd96185..ddd364e208ab 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -83,6 +83,7 @@ struct link_dead_args {
>
> #define NBD_DESTROY_ON_DISCONNECT 0
> #define NBD_DISCONNECT_REQUESTED 1
> +#define NBD_HAS_STARTED 2
>
> struct nbd_config {
> u32 flags;
> @@ -1215,6 +1216,7 @@ static void nbd_config_put(struct nbd_device *nbd)
> nbd->disk->queue->limits.discard_alignment = 0;
> blk_queue_max_discard_sectors(nbd->disk->queue, UINT_MAX);
> blk_queue_flag_clear(QUEUE_FLAG_DISCARD, nbd->disk->queue);
> + clear_bit(NBD_HAS_STARTED, &nbd->flags);
>
> mutex_unlock(&nbd->config_lock);
> nbd_put(nbd);
> @@ -1290,6 +1292,8 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *b
> ret = nbd_start_device(nbd);
> if (ret)
> return ret;
> + else
> + set_bit(NBD_HAS_STARTED, &nbd->flags);
>
> if (max_part)
> bdev->bd_invalidated = 1;
> @@ -1961,6 +1965,7 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
> mutex_unlock(&nbd->config_lock);
> if (!ret) {
> set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
> + set_bit(NBD_HAS_STARTED, &nbd->flags);
> refcount_inc(&nbd->config_refs);
> nbd_connect_reply(info, nbd->index);
> }
> @@ -2008,6 +2013,14 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
> index);
> return -EINVAL;
> }
> +
> + if (!test_bit(NBD_HAS_STARTED, &nbd->flags)) {
> + mutex_unlock(&nbd_index_mutex);
> + printk(KERN_ERR "nbd: device at index %d failed to start\n",
> + index);
> + return -EBUSY;
> + }
> +
> if (!refcount_inc_not_zero(&nbd->refs)) {
> mutex_unlock(&nbd_index_mutex);
> printk(KERN_ERR "nbd: device at index %d is going down\n",
> @@ -2049,6 +2062,14 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
> index);
> return -EINVAL;
> }
> +
> + if (!test_bit(NBD_HAS_STARTED, &nbd->flags)) {
> + mutex_unlock(&nbd_index_mutex);
> + printk(KERN_ERR "nbd: device at index %d failed to start\n",
> + index);
> + return -EBUSY;
> + }
> +
> if (!refcount_inc_not_zero(&nbd->refs)) {
> mutex_unlock(&nbd_index_mutex);
> printk(KERN_ERR "nbd: device at index %d is going down\n",
>
在 2020/1/17 22:18, Josef Bacik 写道:
> On 1/17/20 6:50 AM, Sun Ke wrote:
>> Connect and disconnect a nbd device repeatedly, will cause
>> NULL pointer fault.
>>
>> It will appear by the steps:
>> 1. Connect the nbd device and disconnect it, but now nbd device
>> is not disconnected totally.
>> 2. Connect the same nbd device again immediately, it will fail
>> in nbd_start_device with a EBUSY return value.
>> 3. Wait a second to make sure the last config_refs is reduced
>> and run nbd_config_put to disconnect the nbd device totally.
>> 4. Start another process to open the nbd_device, config_refs
>> will increase and at the same time disconnect it.
>>
>> To fix it, add a NBD_HAS_STARTED flag. Set it in nbd_start_device_ioctl
>> and nbd_genl_connect if nbd device is started successfully.
>> Clear it in nbd_config_put. Test it in nbd_genl_disconnect and
>> nbd_genl_reconfigure.
>
> I don't doubt what you are seeing, but what exactly are we NULL pointer
> dereferencing? I can't quite figure it out from the steps.
The root case is when do disconnect, pointers in structure nbd_device
will not be free immeditily, it should wait for the last config_refs to
be decreased.
I got this kernel NULL pointer dereference report:
[ 256.454582] Dev nbd0: unable to read RDB block 0
[ 256.455611] Dev nbd0: unable to read RDB block 0
[ 256.457528] Dev nbd0: unable to read RDB block 0
[ 256.458742] Dev nbd0: unable to read RDB block 0
[ 256.516375] Dev nbd0: unable to read RDB block 0
[ 257.468970] BUG: kernel NULL pointer dereference, address:
0000000000000020
[ 257.469645] #PF: supervisor write access in kernel mode
[ 257.470445] #PF: error_code(0x0002) - not-present page
[ 257.470888] PGD 12ecb7067 P4D 12ecb7067 PUD 12f3f2067 PMD 0
[ 257.471384] Oops: 0002 [#1] SMP
[ 257.471671] CPU: 1 PID: 1651 Comm: nbd-client Not tainted
5.5.0-rc5-00039-gae6088216ce4 #22
[ 257.472501] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS ?-20180531_142017-buildhw-08.phx2.fedoraproject.org-1.fc28 04/01/2014
[ 257.473776] RIP: 0010:mutex_lock+0x29/0x60
[ 257.474593] Code: 00 0f 1f 44 00 00 53 48 89 fb 48 83 05 cf f8 01 02
01 e8 ea bd ff ff 48 83 05 ca f8 01 02 01 31 c0 65 48 8b 14 25 00 7d 01
00 <f0> 48 0f b1 13 74 f
[ 257.476221] RSP: 0018:ffffc900004cfa10 EFLAGS: 00010246
[ 257.476670] RAX: 0000000000000000 RBX: 0000000000000020 RCX:
0000000000000000
[ 257.477289] RDX: ffff88812f524a00 RSI: ffffffff82e44212 RDI:
0000000000000020
[ 257.477999] RBP: ffffc900004cfab0 R08: ffff88813bc6c110 R09:
0000000000000000
[ 257.478617] R10: 8080808080808080 R11: 0000000000000018 R12:
ffff88813584b000
[ 257.479228] R13: ffffffff838b1f00 R14: ffffc900004cfbb8 R15:
ffffc900004cfa40
[ 257.479871] FS: 00007f0c30d75b40(0000) GS:ffff88813bc40000(0000)
knlGS:0000000000000000
[ 257.480569] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 257.481336] CR2: 0000000000000020 CR3: 000000012f5ea000 CR4:
00000000000006e0
[ 257.481980] Call Trace:
[ 257.482262] flush_workqueue+0x91/0x690
[ 257.482627] ? nbd_size_update+0x180/0x180 [nbd]
[ 257.483063] nbd_disconnect_and_put+0x80/0xd0 [nbd]
[ 257.483497] nbd_genl_disconnect+0x153/0x2d0 [nbd]
[ 257.483969] genl_rcv_msg+0x2ab/0x620
[ 257.484302] ? netlink_unicast+0x3b8/0x5e0
[ 257.484663] ? __nlmsg_put+0x78/0x90
[ 257.485009] ? genl_family_rcv_msg_attrs_parse+0x1a0/0x1a0
[ 257.485488] netlink_rcv_skb+0x5a/0x1a0
[ 257.485849] genl_rcv+0x34/0x60
[ 257.486129] netlink_unicast+0x2a4/0x5e0
[ 257.486468] netlink_sendmsg+0x369/0x6b0
[ 257.486854] ? rw_copy_check_uvector+0x50/0x1d0
[ 257.487257] ____sys_sendmsg+0x1f7/0x370
[ 257.487604] ? copy_msghdr_from_user+0xff/0x1e0
[ 257.488016] ___sys_sendmsg+0x8c/0xe0
[ 257.488335] ? copy_msghdr_from_user+0xff/0x1e0
[ 257.488730] ? ___sys_recvmsg+0xa1/0xe0
[ 257.489091] ? handle_mm_fault+0x199/0x390
[ 257.489454] __sys_sendmsg+0x6b/0xe0
[ 257.489766] __x64_sys_sendmsg+0x23/0x30
[ 257.490149] do_syscall_64+0xab/0x410
[ 257.490474] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 257.490942] RIP: 0033:0x7f0c3047cb87
[ 257.491288] Code: 64 89 02 48 c7 c0 ff ff ff ff eb b9 0f 1f 80 00 00
00 00 8b 05 6a 2b 2c 00 48 63 d2 48 63 ff 85 c0 75 18 b8 2e 00 00 00 0f
05 <48> 3d 00 f0 ff ff 8
[ 257.492940] RSP: 002b:00007ffefb59db28 EFLAGS: 00000246 ORIG_RAX:
000000000000002e
[ 257.493627] RAX: ffffffffffffffda RBX: 00000000023b0120 RCX:
00007f0c3047cb87
[ 257.494497] RDX: 0000000000000000 RSI: 00007ffefb59db60 RDI:
0000000000000003
[ 257.495116] RBP: 00000000023b01f0 R08: 0000000000000014 R09:
0000000000000002
[ 257.495731] R10: 0000000000000006 R11: 0000000000000246 R12:
00000000023b0030
[ 257.496356] R13: 00007ffefb59db60 R14: 0000000000000001 R15:
00000000ffffffff
[ 257.496989] Modules linked in: nbd
[ 257.497580] CR2: 0000000000000020
Thanks,
Ke
>
>>
>> Signed-off-by: Sun Ke <[email protected]>
>> ---
>> drivers/block/nbd.c | 21 +++++++++++++++++++++
>> 1 file changed, 21 insertions(+)
>>
>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>> index b4607dd96185..ddd364e208ab 100644
>> --- a/drivers/block/nbd.c
>> +++ b/drivers/block/nbd.c
>> @@ -83,6 +83,7 @@ struct link_dead_args {
>> #define NBD_DESTROY_ON_DISCONNECT 0
>> #define NBD_DISCONNECT_REQUESTED 1
>> +#define NBD_HAS_STARTED 2
>> struct nbd_config {
>> u32 flags;
>> @@ -1215,6 +1216,7 @@ static void nbd_config_put(struct nbd_device *nbd)
>> nbd->disk->queue->limits.discard_alignment = 0;
>> blk_queue_max_discard_sectors(nbd->disk->queue, UINT_MAX);
>> blk_queue_flag_clear(QUEUE_FLAG_DISCARD, nbd->disk->queue);
>> + clear_bit(NBD_HAS_STARTED, &nbd->flags);
>> mutex_unlock(&nbd->config_lock);
>> nbd_put(nbd);
>> @@ -1290,6 +1292,8 @@ static int nbd_start_device_ioctl(struct
>> nbd_device *nbd, struct block_device *b
>> ret = nbd_start_device(nbd);
>> if (ret)
>> return ret;
>> + else
>> + set_bit(NBD_HAS_STARTED, &nbd->flags);
>
> The else is superfluous here. Thanks,
>
> Josef
>
> .
Thanks for your detailed suggestions.
在 2020/1/18 1:32, Mike Christie 写道:
> On 01/17/2020 05:50 AM, Sun Ke wrote:
>> Connect and disconnect a nbd device repeatedly, will cause
>> NULL pointer fault.
>>
>> It will appear by the steps:
>> 1. Connect the nbd device and disconnect it, but now nbd device
>> is not disconnected totally.
>> 2. Connect the same nbd device again immediately, it will fail
>> in nbd_start_device with a EBUSY return value.
>> 3. Wait a second to make sure the last config_refs is reduced
>> and run nbd_config_put to disconnect the nbd device totally.
>> 4. Start another process to open the nbd_device, config_refs
>> will increase and at the same time disconnect it.
>
> Just to make sure I understood this, for step 4 the process is doing:
>
> open(/dev/nbdX);
> ioctl(NBD_DISCONNECT, /dev/nbdX) or nbd_genl_disconnect(for /dev/nbdX)
>
> ?
>
do nbd_genl_disconnect(for /dev/nbdX)；
I tested it. Connect /dev/nbdX
through ioctl interface by nbd-client -L -N export localhost /dev/nbdX and
through netlink interface by nbd-client localhost XXXX /dev/nbdX,
disconnect /dev/nbdX by nbd-client -d /dev/nbdX.
Both call nbd_genl_disconnect(for /dev/nbdX) and both contain the same
null pointer dereference.
> There is no successful NBD_DO_IT / nbd_genl_connect between the open and
> disconnect calls at step #4, because it would normally be done at #2 and
> that failed. nbd_disconnect_and_put could then reference a null
> recv_workq. If we are also racing with a close() then that could free
> the device/config from under nbd_disconnect_and_put.
>
Yes, nbd_disconnect_and_put could then reference a null recv_workq.
>>
>> To fix it, add a NBD_HAS_STARTED flag. Set it in nbd_start_device_ioctl
>
> I'm not sure if we need the new bit. We could just add a check for a non
> null task_recv in nbd_genl_disconnect like how nbd_start_device and
> nbd_genl_disconnect do.
>
I am also not very sure which is better.
because in nbd_config_put, not only recv_workq is null,
nbd->task_recv and nbd->config the same.
so I doubt that if step 4 do something else will also reference a null
pointer.
> The new bit might be more clear which is nice. If we got this route,
> should the new bit be a runtime_flag like other device state bits?
>
>
Yes, I realize it. Just add a check for a non null task_recv in
nbd_genl_disconnect is better, right?
>> and nbd_genl_connect if nbd device is started successfully.
>> Clear it in nbd_config_put. Test it in nbd_genl_disconnect and
>> nbd_genl_reconfigure.
>>
>> Signed-off-by: Sun Ke <[email protected]>
>> ---
>> drivers/block/nbd.c | 21 +++++++++++++++++++++
>> 1 file changed, 21 insertions(+)
>>
>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>> index b4607dd96185..ddd364e208ab 100644
>> --- a/drivers/block/nbd.c
>> +++ b/drivers/block/nbd.c
>> @@ -83,6 +83,7 @@ struct link_dead_args {
>>
>> #define NBD_DESTROY_ON_DISCONNECT 0
>> #define NBD_DISCONNECT_REQUESTED 1
>> +#define NBD_HAS_STARTED 2
>>
>> struct nbd_config {
>> u32 flags;
>> @@ -1215,6 +1216,7 @@ static void nbd_config_put(struct nbd_device *nbd)
>> nbd->disk->queue->limits.discard_alignment = 0;
>> blk_queue_max_discard_sectors(nbd->disk->queue, UINT_MAX);
>> blk_queue_flag_clear(QUEUE_FLAG_DISCARD, nbd->disk->queue);
>> + clear_bit(NBD_HAS_STARTED, &nbd->flags);
>>
>> mutex_unlock(&nbd->config_lock);
>> nbd_put(nbd);
>> @@ -1290,6 +1292,8 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *b
>> ret = nbd_start_device(nbd);
>> if (ret)
>> return ret;
>> + else
>> + set_bit(NBD_HAS_STARTED, &nbd->flags);
>>
>> if (max_part)
>> bdev->bd_invalidated = 1;
>> @@ -1961,6 +1965,7 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
>> mutex_unlock(&nbd->config_lock);
>> if (!ret) {
>> set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
>> + set_bit(NBD_HAS_STARTED, &nbd->flags);
>> refcount_inc(&nbd->config_refs);
>> nbd_connect_reply(info, nbd->index);
>> }
>> @@ -2008,6 +2013,14 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
>> index);
>> return -EINVAL;
>> }
>> +
>> + if (!test_bit(NBD_HAS_STARTED, &nbd->flags)) {
>> + mutex_unlock(&nbd_index_mutex);
>> + printk(KERN_ERR "nbd: device at index %d failed to start\n",
>> + index);
>> + return -EBUSY;
>> + }
>> +
>> if (!refcount_inc_not_zero(&nbd->refs)) {
>> mutex_unlock(&nbd_index_mutex);
>> printk(KERN_ERR "nbd: device at index %d is going down\n",
>> @@ -2049,6 +2062,14 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
>> index);
>> return -EINVAL;
>> }
>> +
>> + if (!test_bit(NBD_HAS_STARTED, &nbd->flags)) {
>> + mutex_unlock(&nbd_index_mutex);
>> + printk(KERN_ERR "nbd: device at index %d failed to start\n",
>> + index);
>> + return -EBUSY;
>> + }
>> +
>> if (!refcount_inc_not_zero(&nbd->refs)) {
>> mutex_unlock(&nbd_index_mutex);
>> printk(KERN_ERR "nbd: device at index %d is going down\n",
>>
I thought the changes in nbd_genl_reconfigure is necessary althought my
test do not call it. but now I think it is superfluous,
nbd_genl_reconfigure checks for a non null task_recv.
Thanks,
Ke
>
>
> .
>
On 01/19/2020 01:10 AM, sunke (E) wrote:
>
> Thanks for your detailed suggestions.
>
> 在 2020/1/18 1:32, Mike Christie 写道:
>> On 01/17/2020 05:50 AM, Sun Ke wrote:
>>> Connect and disconnect a nbd device repeatedly, will cause
>>> NULL pointer fault.
>>>
>>> It will appear by the steps:
>>> 1. Connect the nbd device and disconnect it, but now nbd device
>>> is not disconnected totally.
>>> 2. Connect the same nbd device again immediately, it will fail
>>> in nbd_start_device with a EBUSY return value.
>>> 3. Wait a second to make sure the last config_refs is reduced
>>> and run nbd_config_put to disconnect the nbd device totally.
>>> 4. Start another process to open the nbd_device, config_refs
>>> will increase and at the same time disconnect it.
>>
>> Just to make sure I understood this, for step 4 the process is doing:
>>
>> open(/dev/nbdX);
>> ioctl(NBD_DISCONNECT, /dev/nbdX) or nbd_genl_disconnect(for /dev/nbdX)
>>
>> ?
>>
> do nbd_genl_disconnect(for /dev/nbdX)；
> I tested it. Connect /dev/nbdX
> through ioctl interface by nbd-client -L -N export localhost /dev/nbdX and
> through netlink interface by nbd-client localhost XXXX /dev/nbdX,
> disconnect /dev/nbdX by nbd-client -d /dev/nbdX.
> Both call nbd_genl_disconnect(for /dev/nbdX) and both contain the same
> null pointer dereference.
>> There is no successful NBD_DO_IT / nbd_genl_connect between the open and
>> disconnect calls at step #4, because it would normally be done at #2 and
>> that failed. nbd_disconnect_and_put could then reference a null
>> recv_workq. If we are also racing with a close() then that could free
>> the device/config from under nbd_disconnect_and_put.
>>
> Yes, nbd_disconnect_and_put could then reference a null recv_workq.
Hey Sunke
How about the attached patch. I am still testing it. The basic idea is
that we need to do a flush whenever we have done a sock_shutdown and are
in the disconnect/connect/clear sock path, so it just adds the flush in
that function. We then do not need to keep adding these flushes everywhere.
Hi Mike
Your idea looks good.
Thanks,
Sun Ke
在 2020/2/10 11:16, Mike Christie 写道:
> On 01/19/2020 01:10 AM, sunke (E) wrote:
>>
>> Thanks for your detailed suggestions.
>>
>> 在 2020/1/18 1:32, Mike Christie 写道:
>>> On 01/17/2020 05:50 AM, Sun Ke wrote:
>>>> Connect and disconnect a nbd device repeatedly, will cause
>>>> NULL pointer fault.
>>>>
>>>> It will appear by the steps:
>>>> 1. Connect the nbd device and disconnect it, but now nbd device
>>>> is not disconnected totally.
>>>> 2. Connect the same nbd device again immediately, it will fail
>>>> in nbd_start_device with a EBUSY return value.
>>>> 3. Wait a second to make sure the last config_refs is reduced
>>>> and run nbd_config_put to disconnect the nbd device totally.
>>>> 4. Start another process to open the nbd_device, config_refs
>>>> will increase and at the same time disconnect it.
>>>
>>> Just to make sure I understood this, for step 4 the process is doing:
>>>
>>> open(/dev/nbdX);
>>> ioctl(NBD_DISCONNECT, /dev/nbdX) or nbd_genl_disconnect(for /dev/nbdX)
>>>
>>> ?
>>>
>> do nbd_genl_disconnect(for /dev/nbdX)；
>> I tested it. Connect /dev/nbdX
>> through ioctl interface by nbd-client -L -N export localhost /dev/nbdX and
>> through netlink interface by nbd-client localhost XXXX /dev/nbdX,
>> disconnect /dev/nbdX by nbd-client -d /dev/nbdX.
>> Both call nbd_genl_disconnect(for /dev/nbdX) and both contain the same
>> null pointer dereference.
>>> There is no successful NBD_DO_IT / nbd_genl_connect between the open and
>>> disconnect calls at step #4, because it would normally be done at #2 and
>>> that failed. nbd_disconnect_and_put could then reference a null
>>> recv_workq. If we are also racing with a close() then that could free
>>> the device/config from under nbd_disconnect_and_put.
>>>
>> Yes, nbd_disconnect_and_put could then reference a null recv_workq.
>
> Hey Sunke
>
> How about the attached patch. I am still testing it. The basic idea is
> that we need to do a flush whenever we have done a sock_shutdown and are
> in the disconnect/connect/clear sock path, so it just adds the flush in
> that function. We then do not need to keep adding these flushes everywhere.
>