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net: bpfilter: disallow to remove bpfilter module while being used
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The bpfilter.ko module can be removed while functions of the bpfilter.ko
are executing. so panic can occurred. in order to protect that, locks can
be used. a bpfilter_lock protects routines in the
__bpfilter_process_sockopt() but it's not enough because __exit routine
can be executed concurrently.

Now, the bpfilter_umh can not run in parallel.
So, the module do not removed while it's being used and it do not
double-create UMH process.
The members of the umh_info and the bpfilter_umh_ops are protected by
the bpfilter_umh_ops.lock.

test commands:
   while :
   do
	iptables -I FORWARD -m string --string ap --algo kmp &
	modprobe -rv bpfilter &
   done

splat looks like:
[  298.623435] BUG: unable to handle kernel paging request at fffffbfff807440b
[  298.628512] #PF error: [normal kernel read fault]
[  298.633018] PGD 124327067 P4D 124327067 PUD 11c1a3067 PMD 119eb2067 PTE 0
[  298.638859] Oops: 0000 [lunn#1] SMP DEBUG_PAGEALLOC KASAN PTI
[  298.638859] CPU: 0 PID: 2997 Comm: iptables Not tainted 4.20.0+ torvalds#154
[  298.638859] RIP: 0010:__mutex_lock+0x6b9/0x16a0
[  298.638859] Code: c0 00 00 e8 89 82 ff ff 80 bd 8f fc ff ff 00 0f 85 d9 05 00 00 48 8b 85 80 fc ff ff 48 bf 00 00 00 00 00 fc ff df 48 c1 e8 03 <80> 3c 38 00 0f 85 1d 0e 00 00 48 8b 85 c8 fc ff ff 49 39 47 58 c6
[  298.638859] RSP: 0018:ffff88810e7777a0 EFLAGS: 00010202
[  298.638859] RAX: 1ffffffff807440b RBX: ffff888111bd4d80 RCX: 0000000000000000
[  298.638859] RDX: 1ffff110235ff806 RSI: ffff888111bd5538 RDI: dffffc0000000000
[  298.638859] RBP: ffff88810e777b30 R08: 0000000080000002 R09: 0000000000000000
[  298.638859] R10: 0000000000000000 R11: 0000000000000000 R12: fffffbfff168a42c
[  298.638859] R13: ffff888111bd4d80 R14: ffff8881040e9a05 R15: ffffffffc03a2000
[  298.638859] FS:  00007f39e3758700(0000) GS:ffff88811ae00000(0000) knlGS:0000000000000000
[  298.638859] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  298.638859] CR2: fffffbfff807440b CR3: 000000011243e000 CR4: 00000000001006f0
[  298.638859] Call Trace:
[  298.638859]  ? mutex_lock_io_nested+0x1560/0x1560
[  298.638859]  ? kasan_kmalloc+0xa0/0xd0
[  298.638859]  ? kmem_cache_alloc+0x1c2/0x260
[  298.638859]  ? __alloc_file+0x92/0x3c0
[  298.638859]  ? alloc_empty_file+0x43/0x120
[  298.638859]  ? alloc_file_pseudo+0x220/0x330
[  298.638859]  ? sock_alloc_file+0x39/0x160
[  298.638859]  ? __sys_socket+0x113/0x1d0
[  298.638859]  ? __x64_sys_socket+0x6f/0xb0
[  298.638859]  ? do_syscall_64+0x138/0x560
[  298.638859]  ? entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  298.638859]  ? __alloc_file+0x92/0x3c0
[  298.638859]  ? init_object+0x6b/0x80
[  298.638859]  ? cyc2ns_read_end+0x10/0x10
[  298.638859]  ? cyc2ns_read_end+0x10/0x10
[  298.638859]  ? hlock_class+0x140/0x140
[  298.638859]  ? sched_clock_local+0xd4/0x140
[  298.638859]  ? sched_clock_local+0xd4/0x140
[  298.638859]  ? check_flags.part.37+0x440/0x440
[  298.638859]  ? __lock_acquire+0x4f90/0x4f90
[  298.638859]  ? set_rq_offline.part.89+0x140/0x140
[ ... ]

Fixes: d2ba09c ("net: add skeleton of bpfilter kernel module")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@TaeheeYoo @ndreys
TaeheeYoo authored and ndreys committed Mar 1, 2019
1 parent 6ed23cd commit cbcda5c
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Showing 3 changed files with 29 additions and 23 deletions.
2 changes: 2 additions & 0 deletions include/linux/bpfilter.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,8 @@ int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval,
int __user *optlen);
struct bpfilter_umh_ops {
struct umh_info info;
/* since ip_getsockopt() can run in parallel, serialize access to umh */
struct mutex lock;
int (*sockopt)(struct sock *sk, int optname,
char __user *optval,
unsigned int optlen, bool is_set);
Expand Down
28 changes: 11 additions & 17 deletions net/bpfilter/bpfilter_kern.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,6 @@
extern char bpfilter_umh_start;
extern char bpfilter_umh_end;

/* since ip_getsockopt() can run in parallel, serialize access to umh */
static DEFINE_MUTEX(bpfilter_lock);

static void shutdown_umh(void)
{
struct task_struct *tsk;
Expand All @@ -36,13 +33,6 @@ static void __stop_umh(void)
shutdown_umh();
}

static void stop_umh(void)
{
mutex_lock(&bpfilter_lock);
__stop_umh();
mutex_unlock(&bpfilter_lock);
}

static int __bpfilter_process_sockopt(struct sock *sk, int optname,
char __user *optval,
unsigned int optlen, bool is_set)
Expand All @@ -58,7 +48,6 @@ static int __bpfilter_process_sockopt(struct sock *sk, int optname,
req.cmd = optname;
req.addr = (long __force __user)optval;
req.len = optlen;
mutex_lock(&bpfilter_lock);
if (!bpfilter_ops.info.pid)
goto out;
n = __kernel_write(bpfilter_ops.info.pipe_to_umh, &req, sizeof(req),
Expand All @@ -80,7 +69,6 @@ static int __bpfilter_process_sockopt(struct sock *sk, int optname,
}
ret = reply.status;
out:
mutex_unlock(&bpfilter_lock);
return ret;
}

Expand All @@ -99,7 +87,7 @@ static int start_umh(void)

/* health check that usermode process started correctly */
if (__bpfilter_process_sockopt(NULL, 0, NULL, 0, 0) != 0) {
stop_umh();
shutdown_umh();
return -EFAULT;
}

Expand All @@ -110,24 +98,30 @@ static int __init load_umh(void)
{
int err;

if (!bpfilter_ops.stop)
return -EFAULT;
mutex_lock(&bpfilter_ops.lock);
if (!bpfilter_ops.stop) {
err = -EFAULT;
goto out;
}
err = start_umh();
if (!err && IS_ENABLED(CONFIG_INET)) {
bpfilter_ops.sockopt = &__bpfilter_process_sockopt;
bpfilter_ops.start = &start_umh;
}

out:
mutex_unlock(&bpfilter_ops.lock);
return err;
}

static void __exit fini_umh(void)
{
mutex_lock(&bpfilter_ops.lock);
if (IS_ENABLED(CONFIG_INET)) {
shutdown_umh();
bpfilter_ops.start = NULL;
bpfilter_ops.sockopt = NULL;
}
stop_umh();
mutex_unlock(&bpfilter_ops.lock);
}
module_init(load_umh);
module_exit(fini_umh);
Expand Down
22 changes: 16 additions & 6 deletions net/ipv4/bpfilter/sockopt.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -14,32 +14,41 @@ EXPORT_SYMBOL_GPL(bpfilter_ops);

static void bpfilter_umh_cleanup(struct umh_info *info)
{
mutex_lock(&bpfilter_ops.lock);
bpfilter_ops.stop = true;
fput(info->pipe_to_umh);
fput(info->pipe_from_umh);
info->pid = 0;
mutex_unlock(&bpfilter_ops.lock);
}

static int bpfilter_mbox_request(struct sock *sk, int optname,
char __user *optval,
unsigned int optlen, bool is_set)
{
int err;

mutex_lock(&bpfilter_ops.lock);
if (!bpfilter_ops.sockopt) {
mutex_unlock(&bpfilter_ops.lock);
err = request_module("bpfilter");
mutex_lock(&bpfilter_ops.lock);

if (err)
return err;
if (!bpfilter_ops.sockopt)
return -ECHILD;
goto out;
if (!bpfilter_ops.sockopt) {
err = -ECHILD;
goto out;
}
}
if (bpfilter_ops.stop) {
err = bpfilter_ops.start();
if (err)
return err;
goto out;
}
return bpfilter_ops.sockopt(sk, optname, optval, optlen, is_set);
err = bpfilter_ops.sockopt(sk, optname, optval, optlen, is_set);
out:
mutex_unlock(&bpfilter_ops.lock);
return err;
}

int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char __user *optval,
Expand All @@ -61,6 +70,7 @@ int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval,

static int __init bpfilter_sockopt_init(void)
{
mutex_init(&bpfilter_ops.lock);
bpfilter_ops.stop = true;
bpfilter_ops.info.cmdline = "bpfilter_umh";
bpfilter_ops.info.cleanup = &bpfilter_umh_cleanup;
Expand Down

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