From: Ye Bin yebin10@huawei.com
[ Upstream commit 0c98057be9efa32de78dbc4685fc73da9d71faa1 ]
I got issue as follows: [ 263.886511] BUG: KASAN: use-after-free in pid_show+0x11f/0x13f [ 263.888359] Read of size 4 at addr ffff8880bf0648c0 by task cat/746 [ 263.890479] CPU: 0 PID: 746 Comm: cat Not tainted 4.19.90-dirty #140 [ 263.893162] Call Trace: [ 263.893509] dump_stack+0x108/0x15f [ 263.893999] print_address_description+0xa5/0x372 [ 263.894641] kasan_report.cold+0x236/0x2a8 [ 263.895696] __asan_report_load4_noabort+0x25/0x30 [ 263.896365] pid_show+0x11f/0x13f [ 263.897422] dev_attr_show+0x48/0x90 [ 263.898361] sysfs_kf_seq_show+0x24d/0x4b0 [ 263.899479] kernfs_seq_show+0x14e/0x1b0 [ 263.900029] seq_read+0x43f/0x1150 [ 263.900499] kernfs_fop_read+0xc7/0x5a0 [ 263.903764] vfs_read+0x113/0x350 [ 263.904231] ksys_read+0x103/0x270 [ 263.905230] __x64_sys_read+0x77/0xc0 [ 263.906284] do_syscall_64+0x106/0x360 [ 263.906797] entry_SYSCALL_64_after_hwframe+0x44/0xa9
Reproduce this issue as follows: 1. nbd-server 8000 /tmp/disk 2. nbd-client localhost 8000 /dev/nbd1 3. cat /sys/block/nbd1/pid Then trigger use-after-free in pid_show.
Reason is after do step '2', nbd-client progress is already exit. So it's task_struct already freed. To solve this issue, revert part of 6521d39a64b3's modify and remove useless 'recv_task' member of nbd_device.
Fixes: 6521d39a64b3 ("nbd: Remove variable 'pid'") Signed-off-by: Ye Bin yebin10@huawei.com Reviewed-by: Josef Bacik josef@toxicpanda.com Link: https://lore.kernel.org/r/20211020073959.2679255-1-yebin10@huawei.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/nbd.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 99ab58b877f8c..6d7e181d3ed1f 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -122,11 +122,11 @@ struct nbd_device { struct work_struct remove_work;
struct list_head list; - struct task_struct *task_recv; struct task_struct *task_setup;
struct completion *destroy_complete; unsigned long flags; + pid_t pid; /* pid of nbd-client, if attached */
char *backend; }; @@ -218,7 +218,7 @@ static ssize_t pid_show(struct device *dev, struct gendisk *disk = dev_to_disk(dev); struct nbd_device *nbd = (struct nbd_device *)disk->private_data;
- return sprintf(buf, "%d\n", task_pid_nr(nbd->task_recv)); + return sprintf(buf, "%d\n", nbd->pid); }
static const struct device_attribute pid_attr = { @@ -362,7 +362,7 @@ static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, nbd->config->bytesize = bytesize; nbd->config->blksize_bits = __ffs(blksize);
- if (!nbd->task_recv) + if (!nbd->pid) return 0;
if (nbd->config->flags & NBD_FLAG_SEND_TRIM) { @@ -1274,7 +1274,7 @@ static void nbd_config_put(struct nbd_device *nbd) if (test_and_clear_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags)) device_remove_file(disk_to_dev(nbd->disk), &pid_attr); - nbd->task_recv = NULL; + nbd->pid = 0; if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags)) { device_remove_file(disk_to_dev(nbd->disk), &backend_attr); @@ -1315,7 +1315,7 @@ static int nbd_start_device(struct nbd_device *nbd) int num_connections = config->num_connections; int error = 0, i;
- if (nbd->task_recv) + if (nbd->pid) return -EBUSY; if (!config->socks) return -EINVAL; @@ -1334,7 +1334,7 @@ static int nbd_start_device(struct nbd_device *nbd) }
blk_mq_update_nr_hw_queues(&nbd->tag_set, config->num_connections); - nbd->task_recv = current; + nbd->pid = task_pid_nr(current);
nbd_parse_flags(nbd);
@@ -1590,8 +1590,8 @@ static int nbd_dbg_tasks_show(struct seq_file *s, void *unused) { struct nbd_device *nbd = s->private;
- if (nbd->task_recv) - seq_printf(s, "recv: %d\n", task_pid_nr(nbd->task_recv)); + if (nbd->pid) + seq_printf(s, "recv: %d\n", nbd->pid);
return 0; } @@ -2177,7 +2177,7 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info) mutex_lock(&nbd->config_lock); config = nbd->config; if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) || - !nbd->task_recv) { + !nbd->pid) { dev_err(nbd_to_dev(nbd), "not configured, cannot reconfigure\n"); ret = -EINVAL;