* [PATCH] nbd: override creds to kernel when calling sock_{send,recv}msg()
@ 2025-10-09 13:45 Ondrej Mosnacek
2025-10-09 14:34 ` Stephen Smalley
2025-10-10 1:56 ` Ming Lei
0 siblings, 2 replies; 4+ messages in thread
From: Ondrej Mosnacek @ 2025-10-09 13:45 UTC (permalink / raw)
To: Josef Bacik, Jens Axboe
Cc: linux-block, nbd, linux-security-module, selinux, Ming Lei
sock_{send,recv}msg() internally calls security_socket_{send,recv}msg(),
which does security checks (e.g. SELinux) for socket access against the
current task. However, _sock_xmit() in drivers/block/nbd.c may be called
indirectly from a userspace syscall, where the NBD socket access would
be incorrectly checked against the calling userspace task (which simply
tries to read/write a file that happens to reside on an NBD device).
To fix this, temporarily override creds to kernel ones before calling
the sock_*() functions. This allows the security modules to recognize
this as internal access by the kernel, which will normally be allowed.
A way to trigger the issue is to do the following (on a system with
SELinux set to enforcing):
### Create nbd device:
truncate -s 256M /tmp/testfile
nbd-server localhost:10809 /tmp/testfile
### Connect to the nbd server:
nbd-client localhost
### Create mdraid array
mdadm --create -l 1 -n 2 /dev/md/testarray /dev/nbd0 missing
### Stop the array
mdadm --stop /dev/md/testarray
### Disconnect the nbd device
nbd-client -d /dev/nbd0
### Reconnect to nbd devices:
nbd-client localhost
After these steps, assuming the SELinux policy doesn't allow the
unexpected access pattern, errors will be visible on the kernel console:
[ 93.997980] nbd2: detected capacity change from 0 to 524288
[ 100.314271] md/raid1:md126: active with 1 out of 2 mirrors
[ 100.314301] md126: detected capacity change from 0 to 522240
[ 100.317288] block nbd2: Send control failed (result -13) <-----
[ 100.317306] block nbd2: Request send failed, requeueing <-----
[ 100.318765] block nbd2: Receive control failed (result -32) <-----
[ 100.318783] block nbd2: Dead connection, failed to find a fallback
[ 100.318794] block nbd2: shutting down sockets
[ 100.318802] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.318817] Buffer I/O error on dev md126, logical block 0, async page read
[ 100.322000] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.322016] Buffer I/O error on dev md126, logical block 0, async page read
[ 100.323244] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.323253] Buffer I/O error on dev md126, logical block 0, async page read
[ 100.324436] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.324444] Buffer I/O error on dev md126, logical block 0, async page read
[ 100.325621] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.325630] Buffer I/O error on dev md126, logical block 0, async page read
[ 100.326813] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.326822] Buffer I/O error on dev md126, logical block 0, async page read
[ 100.326834] md126: unable to read partition table
[ 100.329872] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.329889] Buffer I/O error on dev nbd2, logical block 0, async page read
[ 100.331186] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.331195] Buffer I/O error on dev nbd2, logical block 0, async page read
[ 100.332371] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.332379] Buffer I/O error on dev nbd2, logical block 0, async page read
[ 100.333550] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 100.333559] Buffer I/O error on dev nbd2, logical block 0, async page read
[ 100.334721] nbd2: unable to read partition table
[ 100.350993] nbd2: unable to read partition table
The corresponding SELinux denial on Fedora/RHEL will look like this
(assuming it's not silenced):
type=AVC msg=audit(1758104872.510:116): avc: denied { write } for pid=1908 comm="mdadm" laddr=::1 lport=32772 faddr=::1 fport=10809 scontext=system_u:system_r:mdadm_t:s0-s0:c0.c1023 tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tclass=tcp_socket permissive=0
Cc: Ming Lei <ming.lei@redhat.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2348878
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
---
drivers/block/nbd.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 6463d0e8d0cef..d50055c974a6b 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -52,6 +52,7 @@
static DEFINE_IDR(nbd_index_idr);
static DEFINE_MUTEX(nbd_index_mutex);
static struct workqueue_struct *nbd_del_wq;
+static struct cred *nbd_cred;
static int nbd_total_devices = 0;
struct nbd_sock {
@@ -554,6 +555,7 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
int result;
struct msghdr msg = {} ;
unsigned int noreclaim_flag;
+ const struct cred *old_cred;
if (unlikely(!sock)) {
dev_err_ratelimited(disk_to_dev(nbd->disk),
@@ -562,6 +564,8 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
return -EINVAL;
}
+ old_cred = override_creds(nbd_cred);
+
msg.msg_iter = *iter;
noreclaim_flag = memalloc_noreclaim_save();
@@ -586,6 +590,8 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
memalloc_noreclaim_restore(noreclaim_flag);
+ revert_creds(old_cred);
+
return result;
}
@@ -2669,7 +2675,15 @@ static int __init nbd_init(void)
return -ENOMEM;
}
+ nbd_cred = prepare_kernel_cred(&init_task);
+ if (!nbd_cred) {
+ destroy_workqueue(nbd_del_wq);
+ unregister_blkdev(NBD_MAJOR, "nbd");
+ return -ENOMEM;
+ }
+
if (genl_register_family(&nbd_genl_family)) {
+ put_cred(nbd_cred);
destroy_workqueue(nbd_del_wq);
unregister_blkdev(NBD_MAJOR, "nbd");
return -EINVAL;
@@ -2706,6 +2720,8 @@ static void __exit nbd_cleanup(void)
nbd_dbg_close();
+ put_cred(nbd_cred);
+
mutex_lock(&nbd_index_mutex);
idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
mutex_unlock(&nbd_index_mutex);
--
2.51.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] nbd: override creds to kernel when calling sock_{send,recv}msg()
2025-10-09 13:45 [PATCH] nbd: override creds to kernel when calling sock_{send,recv}msg() Ondrej Mosnacek
@ 2025-10-09 14:34 ` Stephen Smalley
2025-10-09 14:59 ` Paul Moore
2025-10-10 1:56 ` Ming Lei
1 sibling, 1 reply; 4+ messages in thread
From: Stephen Smalley @ 2025-10-09 14:34 UTC (permalink / raw)
To: Ondrej Mosnacek
Cc: Josef Bacik, Jens Axboe, linux-block, nbd, linux-security-module,
selinux, Ming Lei
On Thu, Oct 9, 2025 at 9:45 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
>
> sock_{send,recv}msg() internally calls security_socket_{send,recv}msg(),
> which does security checks (e.g. SELinux) for socket access against the
> current task. However, _sock_xmit() in drivers/block/nbd.c may be called
> indirectly from a userspace syscall, where the NBD socket access would
> be incorrectly checked against the calling userspace task (which simply
> tries to read/write a file that happens to reside on an NBD device).
>
> To fix this, temporarily override creds to kernel ones before calling
> the sock_*() functions. This allows the security modules to recognize
> this as internal access by the kernel, which will normally be allowed.
>
> A way to trigger the issue is to do the following (on a system with
> SELinux set to enforcing):
>
> ### Create nbd device:
> truncate -s 256M /tmp/testfile
> nbd-server localhost:10809 /tmp/testfile
>
> ### Connect to the nbd server:
> nbd-client localhost
>
> ### Create mdraid array
> mdadm --create -l 1 -n 2 /dev/md/testarray /dev/nbd0 missing
>
> ### Stop the array
> mdadm --stop /dev/md/testarray
>
> ### Disconnect the nbd device
> nbd-client -d /dev/nbd0
>
> ### Reconnect to nbd devices:
> nbd-client localhost
>
> After these steps, assuming the SELinux policy doesn't allow the
> unexpected access pattern, errors will be visible on the kernel console:
>
> [ 93.997980] nbd2: detected capacity change from 0 to 524288
> [ 100.314271] md/raid1:md126: active with 1 out of 2 mirrors
> [ 100.314301] md126: detected capacity change from 0 to 522240
> [ 100.317288] block nbd2: Send control failed (result -13) <-----
> [ 100.317306] block nbd2: Request send failed, requeueing <-----
> [ 100.318765] block nbd2: Receive control failed (result -32) <-----
> [ 100.318783] block nbd2: Dead connection, failed to find a fallback
> [ 100.318794] block nbd2: shutting down sockets
> [ 100.318802] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.318817] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.322000] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.322016] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.323244] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.323253] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.324436] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.324444] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.325621] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.325630] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.326813] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.326822] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.326834] md126: unable to read partition table
> [ 100.329872] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.329889] Buffer I/O error on dev nbd2, logical block 0, async page read
> [ 100.331186] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.331195] Buffer I/O error on dev nbd2, logical block 0, async page read
> [ 100.332371] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.332379] Buffer I/O error on dev nbd2, logical block 0, async page read
> [ 100.333550] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.333559] Buffer I/O error on dev nbd2, logical block 0, async page read
> [ 100.334721] nbd2: unable to read partition table
> [ 100.350993] nbd2: unable to read partition table
>
> The corresponding SELinux denial on Fedora/RHEL will look like this
> (assuming it's not silenced):
> type=AVC msg=audit(1758104872.510:116): avc: denied { write } for pid=1908 comm="mdadm" laddr=::1 lport=32772 faddr=::1 fport=10809 scontext=system_u:system_r:mdadm_t:s0-s0:c0.c1023 tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tclass=tcp_socket permissive=0
>
> Cc: Ming Lei <ming.lei@redhat.com>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2348878
> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> ---
> drivers/block/nbd.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 6463d0e8d0cef..d50055c974a6b 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -52,6 +52,7 @@
> static DEFINE_IDR(nbd_index_idr);
> static DEFINE_MUTEX(nbd_index_mutex);
> static struct workqueue_struct *nbd_del_wq;
> +static struct cred *nbd_cred;
> static int nbd_total_devices = 0;
>
> struct nbd_sock {
> @@ -554,6 +555,7 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
> int result;
> struct msghdr msg = {} ;
> unsigned int noreclaim_flag;
> + const struct cred *old_cred;
>
> if (unlikely(!sock)) {
> dev_err_ratelimited(disk_to_dev(nbd->disk),
> @@ -562,6 +564,8 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
> return -EINVAL;
> }
>
> + old_cred = override_creds(nbd_cred);
> +
> msg.msg_iter = *iter;
>
> noreclaim_flag = memalloc_noreclaim_save();
> @@ -586,6 +590,8 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
>
> memalloc_noreclaim_restore(noreclaim_flag);
>
> + revert_creds(old_cred);
> +
> return result;
> }
>
> @@ -2669,7 +2675,15 @@ static int __init nbd_init(void)
> return -ENOMEM;
> }
>
> + nbd_cred = prepare_kernel_cred(&init_task);
> + if (!nbd_cred) {
> + destroy_workqueue(nbd_del_wq);
> + unregister_blkdev(NBD_MAJOR, "nbd");
> + return -ENOMEM;
> + }
> +
> if (genl_register_family(&nbd_genl_family)) {
> + put_cred(nbd_cred);
> destroy_workqueue(nbd_del_wq);
> unregister_blkdev(NBD_MAJOR, "nbd");
> return -EINVAL;
> @@ -2706,6 +2720,8 @@ static void __exit nbd_cleanup(void)
>
> nbd_dbg_close();
>
> + put_cred(nbd_cred);
> +
Should this be done at the end, after the workqueue is destroyed?
> mutex_lock(&nbd_index_mutex);
> idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
> mutex_unlock(&nbd_index_mutex);
> --
> 2.51.0
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] nbd: override creds to kernel when calling sock_{send,recv}msg()
2025-10-09 14:34 ` Stephen Smalley
@ 2025-10-09 14:59 ` Paul Moore
0 siblings, 0 replies; 4+ messages in thread
From: Paul Moore @ 2025-10-09 14:59 UTC (permalink / raw)
To: Stephen Smalley
Cc: Ondrej Mosnacek, Josef Bacik, Jens Axboe, linux-block, nbd,
linux-security-module, selinux, Ming Lei
On Thu, Oct 9, 2025 at 10:34 AM Stephen Smalley
<stephen.smalley.work@gmail.com> wrote:
> On Thu, Oct 9, 2025 at 9:45 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> >
> > sock_{send,recv}msg() internally calls security_socket_{send,recv}msg(),
> > which does security checks (e.g. SELinux) for socket access against the
> > current task. However, _sock_xmit() in drivers/block/nbd.c may be called
> > indirectly from a userspace syscall, where the NBD socket access would
> > be incorrectly checked against the calling userspace task (which simply
> > tries to read/write a file that happens to reside on an NBD device).
> >
> > To fix this, temporarily override creds to kernel ones before calling
> > the sock_*() functions. This allows the security modules to recognize
> > this as internal access by the kernel, which will normally be allowed.
...
> > @@ -2706,6 +2720,8 @@ static void __exit nbd_cleanup(void)
> >
> > nbd_dbg_close();
> >
> > + put_cred(nbd_cred);
> > +
>
> Should this be done at the end, after the workqueue is destroyed?
I didn't trace the send side, but it does look like the receive side
could end up calling into __sock_xmit() while the workqueue is still
alive.
> > mutex_lock(&nbd_index_mutex);
> > idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
> > mutex_unlock(&nbd_index_mutex);
> > --
> > 2.51.0
--
paul-moore.com
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] nbd: override creds to kernel when calling sock_{send,recv}msg()
2025-10-09 13:45 [PATCH] nbd: override creds to kernel when calling sock_{send,recv}msg() Ondrej Mosnacek
2025-10-09 14:34 ` Stephen Smalley
@ 2025-10-10 1:56 ` Ming Lei
1 sibling, 0 replies; 4+ messages in thread
From: Ming Lei @ 2025-10-10 1:56 UTC (permalink / raw)
To: Ondrej Mosnacek
Cc: Josef Bacik, Jens Axboe, linux-block, nbd, linux-security-module,
selinux
On Thu, Oct 09, 2025 at 03:45:42PM +0200, Ondrej Mosnacek wrote:
> sock_{send,recv}msg() internally calls security_socket_{send,recv}msg(),
> which does security checks (e.g. SELinux) for socket access against the
> current task. However, _sock_xmit() in drivers/block/nbd.c may be called
> indirectly from a userspace syscall, where the NBD socket access would
> be incorrectly checked against the calling userspace task (which simply
> tries to read/write a file that happens to reside on an NBD device).
>
> To fix this, temporarily override creds to kernel ones before calling
> the sock_*() functions. This allows the security modules to recognize
> this as internal access by the kernel, which will normally be allowed.
>
> A way to trigger the issue is to do the following (on a system with
> SELinux set to enforcing):
>
> ### Create nbd device:
> truncate -s 256M /tmp/testfile
> nbd-server localhost:10809 /tmp/testfile
>
> ### Connect to the nbd server:
> nbd-client localhost
>
> ### Create mdraid array
> mdadm --create -l 1 -n 2 /dev/md/testarray /dev/nbd0 missing
-EACCESS is triggered when reading data from mdadm process:
@security[mdadm, -13,
handshake_exit+221615650
handshake_exit+221615650
handshake_exit+221616465
security_socket_sendmsg+5
sock_sendmsg+106
handshake_exit+221616150
sock_sendmsg+5
__sock_xmit+162
nbd_send_cmd+597
nbd_handle_cmd+377
nbd_queue_rq+63
blk_mq_dispatch_rq_list+653
__blk_mq_do_dispatch_sched+184
__blk_mq_sched_dispatch_requests+333
blk_mq_sched_dispatch_requests+38
blk_mq_run_hw_queue+239
blk_mq_dispatch_plug_list+382
blk_mq_flush_plug_list.part.0+55
__blk_flush_plug+241
__submit_bio+353
submit_bio_noacct_nocheck+364
submit_bio_wait+84
__blkdev_direct_IO_simple+232
blkdev_read_iter+162
vfs_read+591
ksys_read+95
do_syscall_64+92
entry_SYSCALL_64_after_hwframe+120
]: 1
The issue is started to expose since f1daaaf0c1fa ("block: add plug while submitting IO").
>
> ### Stop the array
> mdadm --stop /dev/md/testarray
>
> ### Disconnect the nbd device
> nbd-client -d /dev/nbd0
>
> ### Reconnect to nbd devices:
> nbd-client localhost
The above steps don't matter actually.
>
> After these steps, assuming the SELinux policy doesn't allow the
> unexpected access pattern, errors will be visible on the kernel console:
>
> [ 93.997980] nbd2: detected capacity change from 0 to 524288
> [ 100.314271] md/raid1:md126: active with 1 out of 2 mirrors
> [ 100.314301] md126: detected capacity change from 0 to 522240
> [ 100.317288] block nbd2: Send control failed (result -13) <-----
> [ 100.317306] block nbd2: Request send failed, requeueing <-----
> [ 100.318765] block nbd2: Receive control failed (result -32) <-----
> [ 100.318783] block nbd2: Dead connection, failed to find a fallback
> [ 100.318794] block nbd2: shutting down sockets
> [ 100.318802] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.318817] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.322000] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.322016] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.323244] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.323253] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.324436] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.324444] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.325621] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.325630] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.326813] I/O error, dev nbd2, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.326822] Buffer I/O error on dev md126, logical block 0, async page read
> [ 100.326834] md126: unable to read partition table
> [ 100.329872] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.329889] Buffer I/O error on dev nbd2, logical block 0, async page read
> [ 100.331186] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.331195] Buffer I/O error on dev nbd2, logical block 0, async page read
> [ 100.332371] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.332379] Buffer I/O error on dev nbd2, logical block 0, async page read
> [ 100.333550] I/O error, dev nbd2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> [ 100.333559] Buffer I/O error on dev nbd2, logical block 0, async page read
> [ 100.334721] nbd2: unable to read partition table
> [ 100.350993] nbd2: unable to read partition table
>
> The corresponding SELinux denial on Fedora/RHEL will look like this
> (assuming it's not silenced):
> type=AVC msg=audit(1758104872.510:116): avc: denied { write } for pid=1908 comm="mdadm" laddr=::1 lport=32772 faddr=::1 fport=10809 scontext=system_u:system_r:mdadm_t:s0-s0:c0.c1023 tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tclass=tcp_socket permissive=0
>
> Cc: Ming Lei <ming.lei@redhat.com>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2348878
> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> ---
> drivers/block/nbd.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 6463d0e8d0cef..d50055c974a6b 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -52,6 +52,7 @@
> static DEFINE_IDR(nbd_index_idr);
> static DEFINE_MUTEX(nbd_index_mutex);
> static struct workqueue_struct *nbd_del_wq;
> +static struct cred *nbd_cred;
> static int nbd_total_devices = 0;
>
> struct nbd_sock {
> @@ -554,6 +555,7 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
> int result;
> struct msghdr msg = {} ;
> unsigned int noreclaim_flag;
> + const struct cred *old_cred;
>
> if (unlikely(!sock)) {
> dev_err_ratelimited(disk_to_dev(nbd->disk),
> @@ -562,6 +564,8 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
> return -EINVAL;
> }
>
> + old_cred = override_creds(nbd_cred);
> +
> msg.msg_iter = *iter;
>
> noreclaim_flag = memalloc_noreclaim_save();
> @@ -586,6 +590,8 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
>
> memalloc_noreclaim_restore(noreclaim_flag);
>
> + revert_creds(old_cred);
> +
> return result;
> }
>
> @@ -2669,7 +2675,15 @@ static int __init nbd_init(void)
> return -ENOMEM;
> }
>
> + nbd_cred = prepare_kernel_cred(&init_task);
> + if (!nbd_cred) {
> + destroy_workqueue(nbd_del_wq);
> + unregister_blkdev(NBD_MAJOR, "nbd");
> + return -ENOMEM;
> + }
> +
> if (genl_register_family(&nbd_genl_family)) {
> + put_cred(nbd_cred);
> destroy_workqueue(nbd_del_wq);
> unregister_blkdev(NBD_MAJOR, "nbd");
> return -EINVAL;
> @@ -2706,6 +2720,8 @@ static void __exit nbd_cleanup(void)
>
> nbd_dbg_close();
>
> + put_cred(nbd_cred);
> +
> mutex_lock(&nbd_index_mutex);
> idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
> mutex_unlock(&nbd_index_mutex);
Yeah, as commented by Stephen and Paul, put_cred() need to be moved after
destroy_workqueue(nbd_del_wq) in which wq function nbd disk is removed and
recv wq is destroyed.
Otherwise, this patch looks fine from block layer viewpoint, and I verified
that it does fix the -EACCESS failure for madadm to read from nbd.
Thanks,
Ming
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2025-10-10 1:56 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-10-09 13:45 [PATCH] nbd: override creds to kernel when calling sock_{send,recv}msg() Ondrej Mosnacek
2025-10-09 14:34 ` Stephen Smalley
2025-10-09 14:59 ` Paul Moore
2025-10-10 1:56 ` Ming Lei
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