| Message ID | 20210128074153.1633374-1-sunke32@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | nbd: Fix NULL pointer in flush_workqueue | expand |
hi，Markus 在 2021/1/29 3:42, Markus Elfring 写道: > … >> +++ b/drivers/block/nbd.c >> @@ -2011,12 +2011,20 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info) >> index); >> return -EINVAL; >> } >> + mutex_lock(&nbd->config_lock); >> if (!refcount_inc_not_zero(&nbd->refs)) { >> mutex_unlock(&nbd_index_mutex); >> + mutex_unlock(&nbd->config_lock); > Can an other function call order become relevant for the unlocking of these mutexes? Do you think the nbd->config_lock mutex here is useless? > > >> printk(KERN_ERR "nbd: device at index %d is going down\n", >> index); > May such an error message be moved into the lock scope? Sure. > > >> return -EINVAL; >> } >> + if (!nbd->recv_workq) { >> + mutex_unlock(&nbd->config_lock); >> + mutex_unlock(&nbd_index_mutex); >> + return -EINVAL; >> + } > How do you think about to connect the code from this if branch > with a jump target like “unlock” so that such statements would be shareable > for the desired exception handling? OK, I will improve it in V2 patch. > > >> + mutex_unlock(&nbd->config_lock); >> mutex_unlock(&nbd_index_mutex); >> if (!refcount_inc_not_zero(&nbd->config_refs)) { >> nbd_put(nbd); > > Regards, > Markus > .
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 6727358e147d..4f7885966d32 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -2011,12 +2011,20 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info) index); return -EINVAL; } + mutex_lock(&nbd->config_lock); if (!refcount_inc_not_zero(&nbd->refs)) { mutex_unlock(&nbd_index_mutex); + mutex_unlock(&nbd->config_lock); printk(KERN_ERR "nbd: device at index %d is going down\n", index); return -EINVAL; } + if (!nbd->recv_workq) { + mutex_unlock(&nbd->config_lock); + mutex_unlock(&nbd_index_mutex); + return -EINVAL; + } + mutex_unlock(&nbd->config_lock); mutex_unlock(&nbd_index_mutex); if (!refcount_inc_not_zero(&nbd->config_refs)) { nbd_put(nbd);
Open /dev/nbdX first, the config_refs will be 1 and the pointers in nbd_device are still null. Disconnect /dev/nbdX, then reference a null recv_workq. The protection by config_refs in nbd_genl_disconnect is useless. [ 656.366194] BUG: kernel NULL pointer dereference, address: 0000000000000020 [ 656.368943] #PF: supervisor write access in kernel mode [ 656.369844] #PF: error_code(0x0002) - not-present page [ 656.370717] PGD 10cc87067 P4D 10cc87067 PUD 1074b4067 PMD 0 [ 656.371693] Oops: 0002 [#1] SMP [ 656.372242] CPU: 5 PID: 7977 Comm: nbd-client Not tainted 5.11.0-rc5-00040-g76c057c84d28 #1 [ 656.373661] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014 [ 656.375904] RIP: 0010:mutex_lock+0x29/0x60 [ 656.376627] Code: 00 0f 1f 44 00 00 55 48 89 fd 48 83 05 6f d7 fe 08 01 e8 7a c3 ff ff 48 83 05 6a d7 fe 08 01 31 c0 65 48 8b 14 25 00 6d 01 00 <f0> 48 0f b1 55 d [ 656.378934] RSP: 0018:ffffc900005eb9b0 EFLAGS: 00010246 [ 656.379350] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 656.379915] RDX: ffff888104cf2600 RSI: ffffffffaae8f452 RDI: 0000000000000020 [ 656.380473] RBP: 0000000000000020 R08: 0000000000000000 R09: ffff88813bd6b318 [ 656.381039] R10: 00000000000000c7 R11: fefefefefefefeff R12: ffff888102710b40 [ 656.381599] R13: ffffc900005eb9e0 R14: ffffffffb2930680 R15: ffff88810770ef00 [ 656.382166] FS: 00007fdf117ebb40(0000) GS:ffff88813bd40000(0000) knlGS:0000000000000000 [ 656.382806] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 656.383261] CR2: 0000000000000020 CR3: 0000000100c84000 CR4: 00000000000006e0 [ 656.383819] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 656.384370] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 656.384927] Call Trace: [ 656.385111] flush_workqueue+0x92/0x6c0 [ 656.385395] nbd_disconnect_and_put+0x81/0xd0 [ 656.385716] nbd_genl_disconnect+0x125/0x2a0 [ 656.386034] genl_family_rcv_msg_doit.isra.0+0x102/0x1b0 [ 656.386422] genl_rcv_msg+0xfc/0x2b0 [ 656.386685] ? nbd_ioctl+0x490/0x490 [ 656.386954] ? genl_family_rcv_msg_doit.isra.0+0x1b0/0x1b0 [ 656.387354] netlink_rcv_skb+0x62/0x180 [ 656.387638] genl_rcv+0x34/0x60 [ 656.387874] netlink_unicast+0x26d/0x590 [ 656.388162] netlink_sendmsg+0x398/0x6c0 [ 656.388451] ? netlink_rcv_skb+0x180/0x180 [ 656.388750] ____sys_sendmsg+0x1da/0x320 [ 656.389038] ? ____sys_recvmsg+0x130/0x220 [ 656.389334] ___sys_sendmsg+0x8e/0xf0 [ 656.389605] ? ___sys_recvmsg+0xa2/0xf0 [ 656.389889] ? handle_mm_fault+0x1671/0x21d0 [ 656.390201] __sys_sendmsg+0x6d/0xe0 [ 656.390464] __x64_sys_sendmsg+0x23/0x30 [ 656.390751] do_syscall_64+0x45/0x70 [ 656.391017] entry_SYSCALL_64_after_hwframe+0x44/0xa9 To fix it, just add a check for a non null task_recv in nbd_genl_disconnect. Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs") Signed-off-by: Sun Ke <sunke32@huawei.com> --- drivers/block/nbd.c | 8 ++++++++ 1 file changed, 8 insertions(+)