[PATCH -next] nbd: Fix use-after-free in pid_show
From: Ye Bin <hidden>
Date: 2021-10-20 07:27:30
Also in:
lkml
Subsystem:
block layer, network block device (nbd), the rest · Maintainers:
Jens Axboe, Josef Bacik, Linus Torvalds
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 <redacted>
---
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 0d064fab6186..0ee104fbb628 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c@@ -122,10 +122,10 @@ struct nbd_device { struct work_struct remove_work; struct list_head list; - struct task_struct *task_recv; struct task_struct *task_setup; unsigned long flags; + pid_t pid; /* pid of nbd-client, if attached */ char *backend; };
@@ -223,7 +223,7 @@ 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 = {
@@ -335,7 +335,7 @@ 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) {
@@ -1300,7 +1300,7 @@ 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);
@@ -1341,7 +1341,7 @@ 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;
@@ -1360,7 +1360,7 @@ 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);
@@ -1616,8 +1616,8 @@ 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; }
@@ -2198,7 +2198,7 @@ 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;
--
2.31.1