[PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Du Cheng]

add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
due to internal use of per_cpu variables, which requires preemption
disabling/enabling.

reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller

Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
Signed-off-by: Du Cheng <ducheng2@gmail.com>
---
changelog
v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
v2: revert to GFP_ATOMIC but add preemption disable/enable protection

 net/qrtr/qrtr.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
index edb6ac17ceca..6361f169490e 100644
--- a/net/qrtr/qrtr.c
+++ b/net/qrtr/qrtr.c
@@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
 	mutex_lock(&qrtr_port_lock);
 	if (!*port) {
 		min_port = QRTR_MIN_EPH_SOCKET;
+		idr_preload(GFP_ATOMIC);
 		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
+		idr_preload_end();
 		if (!rc)
 			*port = min_port;
 	} else if (*port < QRTR_MIN_EPH_SOCKET && !capable(CAP_NET_ADMIN)) {
 		rc = -EACCES;
 	} else if (*port == QRTR_PORT_CTRL) {
 		min_port = 0;
+		idr_preload(GFP_ATOMIC);
 		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, 0, GFP_ATOMIC);
+		idr_preload_end();
 	} else {
 		min_port = *port;
+		idr_preload(GFP_ATOMIC);
 		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, *port, GFP_ATOMIC);
+		idr_preload_end();
 		if (!rc)
 			*port = min_port;
 	}
-- 
2.27.0

Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Greg Kroah-Hartman]

Adding the xarray maintainer...

On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> due to internal use of per_cpu variables, which requires preemption
> disabling/enabling.
> 
> reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> 
> Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> Signed-off-by: Du Cheng <ducheng2@gmail.com>
> ---
> changelog
> v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> 
>  net/qrtr/qrtr.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> index edb6ac17ceca..6361f169490e 100644
> --- a/net/qrtr/qrtr.c
> +++ b/net/qrtr/qrtr.c
> @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
>  	mutex_lock(&qrtr_port_lock);
>  	if (!*port) {
>  		min_port = QRTR_MIN_EPH_SOCKET;
> +		idr_preload(GFP_ATOMIC);
>  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> +		idr_preload_end();

This seems "odd" to me.  We are asking idr_alloc_u32() to abide by
GFP_ATOMIC, so why do we need to "preload" it with the same type of
allocation?

Is there something in the idr/radix/xarray code that can't really handle
GFP_ATOMIC during a "normal" idr allocation that is causing this warning
to be hit?  Why is this change the "correct" one?

thanks,

greg k-h

Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Du Cheng]

On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote:
> Adding the xarray maintainer...
> 
> On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> > due to internal use of per_cpu variables, which requires preemption
> > disabling/enabling.
> > 
> > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> > 
> > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> > Signed-off-by: Du Cheng <ducheng2@gmail.com>
> > ---
> > changelog
> > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> > v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> > 
> >  net/qrtr/qrtr.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> > index edb6ac17ceca..6361f169490e 100644
> > --- a/net/qrtr/qrtr.c
> > +++ b/net/qrtr/qrtr.c
> > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> >  	mutex_lock(&qrtr_port_lock);
> >  	if (!*port) {
> >  		min_port = QRTR_MIN_EPH_SOCKET;
> > +		idr_preload(GFP_ATOMIC);
> >  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> > +		idr_preload_end();
> 
> This seems "odd" to me.  We are asking idr_alloc_u32() to abide by
> GFP_ATOMIC, so why do we need to "preload" it with the same type of
> allocation?
> 
> Is there something in the idr/radix/xarray code that can't really handle
> GFP_ATOMIC during a "normal" idr allocation that is causing this warning
> to be hit?  Why is this change the "correct" one?
> 
> thanks,
> 
> greg k-h


From the comment above idr_preload() in lib/radix-tree.c:1460
/**
 * idr_preload - preload for idr_alloc()
 * @gfp_mask: allocation mask to use for preloading
 *
 * Preallocate memory to use for the next call to idr_alloc().  This function
 * returns with preemption disabled.  It will be enabled by idr_preload_end().
 */

idr_alloc is a very simple wrapper around idr_alloc_u32().

On top of radix_tree_node_alloc() which is called by idr_alloc_u32(), there is
this comment at line 244 in the same radix-tree.c
/*
 * This assumes that the caller has performed appropriate preallocation, and
 * that the caller has pinned this thread of control to the current CPU.
 */

Therefore the preload/preload_end are necessary, or at least should have
preemption disabled

Regards,
Du Cheng

Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Greg Kroah-Hartman]

On Sat, Mar 27, 2021 at 10:25:20PM +0800, Du Cheng wrote:
> On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote:
> > Adding the xarray maintainer...
> > 
> > On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> > > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> > > due to internal use of per_cpu variables, which requires preemption
> > > disabling/enabling.
> > > 
> > > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> > > 
> > > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> > > Signed-off-by: Du Cheng <ducheng2@gmail.com>
> > > ---
> > > changelog
> > > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> > > v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> > > 
> > >  net/qrtr/qrtr.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> > > index edb6ac17ceca..6361f169490e 100644
> > > --- a/net/qrtr/qrtr.c
> > > +++ b/net/qrtr/qrtr.c
> > > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> > >  	mutex_lock(&qrtr_port_lock);
> > >  	if (!*port) {
> > >  		min_port = QRTR_MIN_EPH_SOCKET;
> > > +		idr_preload(GFP_ATOMIC);
> > >  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> > > +		idr_preload_end();
> > 
> > This seems "odd" to me.  We are asking idr_alloc_u32() to abide by
> > GFP_ATOMIC, so why do we need to "preload" it with the same type of
> > allocation?
> > 
> > Is there something in the idr/radix/xarray code that can't really handle
> > GFP_ATOMIC during a "normal" idr allocation that is causing this warning
> > to be hit?  Why is this change the "correct" one?
> > 
> > thanks,
> > 
> > greg k-h
> 
> 
> >From the comment above idr_preload() in lib/radix-tree.c:1460
> /**
>  * idr_preload - preload for idr_alloc()
>  * @gfp_mask: allocation mask to use for preloading
>  *
>  * Preallocate memory to use for the next call to idr_alloc().  This function
>  * returns with preemption disabled.  It will be enabled by idr_preload_end().
>  */
> 
> idr_alloc is a very simple wrapper around idr_alloc_u32().
> 
> On top of radix_tree_node_alloc() which is called by idr_alloc_u32(), there is
> this comment at line 244 in the same radix-tree.c
> /*
>  * This assumes that the caller has performed appropriate preallocation, and
>  * that the caller has pinned this thread of control to the current CPU.
>  */
> 
> Therefore the preload/preload_end are necessary, or at least should have
> preemption disabled

Ah, so it's disabling preemption that is the key here.  Still odd, why
is GFP_ATOMIC not sufficient in a normal idr_alloc() call to keep things
from doing stuff like this?  Feels like a lot of "internal knowledge" is
needed here to use this api properly...

Matthew, is the above change really correct?

thanks,

greg k-h

Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Matthew Wilcox]

On Sat, Mar 27, 2021 at 03:31:18PM +0100, Greg Kroah-Hartman wrote:
> On Sat, Mar 27, 2021 at 10:25:20PM +0800, Du Cheng wrote:
> > On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote:
> > > Adding the xarray maintainer...
> > > 
> > > On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> > > > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> > > > due to internal use of per_cpu variables, which requires preemption
> > > > disabling/enabling.
> > > > 
> > > > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> > > > 
> > > > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> > > > Signed-off-by: Du Cheng <ducheng2@gmail.com>
> > > > ---
> > > > changelog
> > > > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> > > > v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> > > > 
> > > >  net/qrtr/qrtr.c | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > > 
> > > > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> > > > index edb6ac17ceca..6361f169490e 100644
> > > > --- a/net/qrtr/qrtr.c
> > > > +++ b/net/qrtr/qrtr.c
> > > > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> > > >  	mutex_lock(&qrtr_port_lock);
> > > >  	if (!*port) {
> > > >  		min_port = QRTR_MIN_EPH_SOCKET;
> > > > +		idr_preload(GFP_ATOMIC);
> > > >  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> > > > +		idr_preload_end();
> > > 
> > > This seems "odd" to me.  We are asking idr_alloc_u32() to abide by
> > > GFP_ATOMIC, so why do we need to "preload" it with the same type of
> > > allocation?
> > > 
> > > Is there something in the idr/radix/xarray code that can't really handle
> > > GFP_ATOMIC during a "normal" idr allocation that is causing this warning
> > > to be hit?  Why is this change the "correct" one?
> > > 
> > > thanks,
> > > 
> > > greg k-h
> > 
> > 
> > >From the comment above idr_preload() in lib/radix-tree.c:1460
> > /**
> >  * idr_preload - preload for idr_alloc()
> >  * @gfp_mask: allocation mask to use for preloading
> >  *
> >  * Preallocate memory to use for the next call to idr_alloc().  This function
> >  * returns with preemption disabled.  It will be enabled by idr_preload_end().
> >  */
> > 
> > idr_alloc is a very simple wrapper around idr_alloc_u32().
> > 
> > On top of radix_tree_node_alloc() which is called by idr_alloc_u32(), there is
> > this comment at line 244 in the same radix-tree.c
> > /*
> >  * This assumes that the caller has performed appropriate preallocation, and
> >  * that the caller has pinned this thread of control to the current CPU.
> >  */
> > 
> > Therefore the preload/preload_end are necessary, or at least should have
> > preemption disabled
> 
> Ah, so it's disabling preemption that is the key here.  Still odd, why
> is GFP_ATOMIC not sufficient in a normal idr_alloc() call to keep things
> from doing stuff like this?  Feels like a lot of "internal knowledge" is
> needed here to use this api properly...
> 
> Matthew, is the above change really correct?

No.

https://lore.kernel.org/netdev/20200605112922.GB19604@bombadil.infradead.org/
https://lore.kernel.org/netdev/20200605120037.17427-1-willy@infradead.org/
https://lore.kernel.org/netdev/20200914192655.GW6583@casper.infradead.org/

Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Greg Kroah-Hartman]

On Sat, Mar 27, 2021 at 03:51:10PM +0000, Matthew Wilcox wrote:
> On Sat, Mar 27, 2021 at 03:31:18PM +0100, Greg Kroah-Hartman wrote:
> > On Sat, Mar 27, 2021 at 10:25:20PM +0800, Du Cheng wrote:
> > > On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote:
> > > > Adding the xarray maintainer...
> > > > 
> > > > On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> > > > > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> > > > > due to internal use of per_cpu variables, which requires preemption
> > > > > disabling/enabling.
> > > > > 
> > > > > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> > > > > 
> > > > > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> > > > > Signed-off-by: Du Cheng <ducheng2@gmail.com>
> > > > > ---
> > > > > changelog
> > > > > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> > > > > v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> > > > > 
> > > > >  net/qrtr/qrtr.c | 6 ++++++
> > > > >  1 file changed, 6 insertions(+)
> > > > > 
> > > > > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> > > > > index edb6ac17ceca..6361f169490e 100644
> > > > > --- a/net/qrtr/qrtr.c
> > > > > +++ b/net/qrtr/qrtr.c
> > > > > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> > > > >  	mutex_lock(&qrtr_port_lock);
> > > > >  	if (!*port) {
> > > > >  		min_port = QRTR_MIN_EPH_SOCKET;
> > > > > +		idr_preload(GFP_ATOMIC);
> > > > >  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> > > > > +		idr_preload_end();
> > > > 
> > > > This seems "odd" to me.  We are asking idr_alloc_u32() to abide by
> > > > GFP_ATOMIC, so why do we need to "preload" it with the same type of
> > > > allocation?
> > > > 
> > > > Is there something in the idr/radix/xarray code that can't really handle
> > > > GFP_ATOMIC during a "normal" idr allocation that is causing this warning
> > > > to be hit?  Why is this change the "correct" one?
> > > > 
> > > > thanks,
> > > > 
> > > > greg k-h
> > > 
> > > 
> > > >From the comment above idr_preload() in lib/radix-tree.c:1460
> > > /**
> > >  * idr_preload - preload for idr_alloc()
> > >  * @gfp_mask: allocation mask to use for preloading
> > >  *
> > >  * Preallocate memory to use for the next call to idr_alloc().  This function
> > >  * returns with preemption disabled.  It will be enabled by idr_preload_end().
> > >  */
> > > 
> > > idr_alloc is a very simple wrapper around idr_alloc_u32().
> > > 
> > > On top of radix_tree_node_alloc() which is called by idr_alloc_u32(), there is
> > > this comment at line 244 in the same radix-tree.c
> > > /*
> > >  * This assumes that the caller has performed appropriate preallocation, and
> > >  * that the caller has pinned this thread of control to the current CPU.
> > >  */
> > > 
> > > Therefore the preload/preload_end are necessary, or at least should have
> > > preemption disabled
> > 
> > Ah, so it's disabling preemption that is the key here.  Still odd, why
> > is GFP_ATOMIC not sufficient in a normal idr_alloc() call to keep things
> > from doing stuff like this?  Feels like a lot of "internal knowledge" is
> > needed here to use this api properly...
> > 
> > Matthew, is the above change really correct?
> 
> No.
> 
> https://lore.kernel.org/netdev/20200605112922.GB19604@bombadil.infradead.org/
> https://lore.kernel.org/netdev/20200605120037.17427-1-willy@infradead.org/
> https://lore.kernel.org/netdev/20200914192655.GW6583@casper.infradead.org/
> 

Ok, it looks like this code is just abandonded, should we remove it
entirely as no one wants to maintain it?

thanks,

greg k-h

Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Matthew Wilcox]

On Sun, Mar 28, 2021 at 08:56:17AM +0200, Greg Kroah-Hartman wrote:
> On Sat, Mar 27, 2021 at 03:51:10PM +0000, Matthew Wilcox wrote:
> > On Sat, Mar 27, 2021 at 03:31:18PM +0100, Greg Kroah-Hartman wrote:
> > > On Sat, Mar 27, 2021 at 10:25:20PM +0800, Du Cheng wrote:
> > > > On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote:
> > > > > Adding the xarray maintainer...
> > > > > 
> > > > > On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> > > > > > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> > > > > > due to internal use of per_cpu variables, which requires preemption
> > > > > > disabling/enabling.
> > > > > > 
> > > > > > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> > > > > > 
> > > > > > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> > > > > > Signed-off-by: Du Cheng <ducheng2@gmail.com>
> > > > > > ---
> > > > > > changelog
> > > > > > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> > > > > > v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> > > > > > 
> > > > > >  net/qrtr/qrtr.c | 6 ++++++
> > > > > >  1 file changed, 6 insertions(+)
> > > > > > 
> > > > > > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> > > > > > index edb6ac17ceca..6361f169490e 100644
> > > > > > --- a/net/qrtr/qrtr.c
> > > > > > +++ b/net/qrtr/qrtr.c
> > > > > > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> > > > > >  	mutex_lock(&qrtr_port_lock);
> > > > > >  	if (!*port) {
> > > > > >  		min_port = QRTR_MIN_EPH_SOCKET;
> > > > > > +		idr_preload(GFP_ATOMIC);
> > > > > >  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> > > > > > +		idr_preload_end();
> > > > > 
> > > > > This seems "odd" to me.  We are asking idr_alloc_u32() to abide by
> > > > > GFP_ATOMIC, so why do we need to "preload" it with the same type of
> > > > > allocation?
> > > > > 
> > > > > Is there something in the idr/radix/xarray code that can't really handle
> > > > > GFP_ATOMIC during a "normal" idr allocation that is causing this warning
> > > > > to be hit?  Why is this change the "correct" one?
> > > > > 
> > > > > thanks,
> > > > > 
> > > > > greg k-h
> > > > 
> > > > 
> > > > >From the comment above idr_preload() in lib/radix-tree.c:1460
> > > > /**
> > > >  * idr_preload - preload for idr_alloc()
> > > >  * @gfp_mask: allocation mask to use for preloading
> > > >  *
> > > >  * Preallocate memory to use for the next call to idr_alloc().  This function
> > > >  * returns with preemption disabled.  It will be enabled by idr_preload_end().
> > > >  */
> > > > 
> > > > idr_alloc is a very simple wrapper around idr_alloc_u32().
> > > > 
> > > > On top of radix_tree_node_alloc() which is called by idr_alloc_u32(), there is
> > > > this comment at line 244 in the same radix-tree.c
> > > > /*
> > > >  * This assumes that the caller has performed appropriate preallocation, and
> > > >  * that the caller has pinned this thread of control to the current CPU.
> > > >  */
> > > > 
> > > > Therefore the preload/preload_end are necessary, or at least should have
> > > > preemption disabled
> > > 
> > > Ah, so it's disabling preemption that is the key here.  Still odd, why
> > > is GFP_ATOMIC not sufficient in a normal idr_alloc() call to keep things
> > > from doing stuff like this?  Feels like a lot of "internal knowledge" is
> > > needed here to use this api properly...
> > > 
> > > Matthew, is the above change really correct?
> > 
> > No.
> > 
> > https://lore.kernel.org/netdev/20200605112922.GB19604@bombadil.infradead.org/
> > https://lore.kernel.org/netdev/20200605120037.17427-1-willy@infradead.org/
> > https://lore.kernel.org/netdev/20200914192655.GW6583@casper.infradead.org/
> > 
> 
> Ok, it looks like this code is just abandonded, should we remove it
> entirely as no one wants to maintain it?

Fine by me.  I don't use it.  Better to get rid of abandonware than keep
a potential source of security holes.

Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Du Cheng]

On Sun, Mar 28, 2021 at 11:04:17AM +0100, Matthew Wilcox wrote:
> On Sun, Mar 28, 2021 at 08:56:17AM +0200, Greg Kroah-Hartman wrote:
> > On Sat, Mar 27, 2021 at 03:51:10PM +0000, Matthew Wilcox wrote:
> > > On Sat, Mar 27, 2021 at 03:31:18PM +0100, Greg Kroah-Hartman wrote:
> > > > On Sat, Mar 27, 2021 at 10:25:20PM +0800, Du Cheng wrote:
> > > > > On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote:
> > > > > > Adding the xarray maintainer...
> > > > > > 
> > > > > > On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> > > > > > > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> > > > > > > due to internal use of per_cpu variables, which requires preemption
> > > > > > > disabling/enabling.
> > > > > > > 
> > > > > > > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> > > > > > > 
> > > > > > > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> > > > > > > Signed-off-by: Du Cheng <ducheng2@gmail.com>
> > > > > > > ---
> > > > > > > changelog
> > > > > > > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> > > > > > > v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> > > > > > > 
> > > > > > >  net/qrtr/qrtr.c | 6 ++++++
> > > > > > >  1 file changed, 6 insertions(+)
> > > > > > > 
> > > > > > > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> > > > > > > index edb6ac17ceca..6361f169490e 100644
> > > > > > > --- a/net/qrtr/qrtr.c
> > > > > > > +++ b/net/qrtr/qrtr.c
> > > > > > > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> > > > > > >  	mutex_lock(&qrtr_port_lock);
> > > > > > >  	if (!*port) {
> > > > > > >  		min_port = QRTR_MIN_EPH_SOCKET;
> > > > > > > +		idr_preload(GFP_ATOMIC);
> > > > > > >  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> > > > > > > +		idr_preload_end();
> > > > > > 
> > > > > > This seems "odd" to me.  We are asking idr_alloc_u32() to abide by
> > > > > > GFP_ATOMIC, so why do we need to "preload" it with the same type of
> > > > > > allocation?
> > > > > > 
> > > > > > Is there something in the idr/radix/xarray code that can't really handle
> > > > > > GFP_ATOMIC during a "normal" idr allocation that is causing this warning
> > > > > > to be hit?  Why is this change the "correct" one?
> > > > > > 
> > > > > > thanks,
> > > > > > 
> > > > > > greg k-h
> > > > > 
> > > > > 
> > > > > >From the comment above idr_preload() in lib/radix-tree.c:1460
> > > > > /**
> > > > >  * idr_preload - preload for idr_alloc()
> > > > >  * @gfp_mask: allocation mask to use for preloading
> > > > >  *
> > > > >  * Preallocate memory to use for the next call to idr_alloc().  This function
> > > > >  * returns with preemption disabled.  It will be enabled by idr_preload_end().
> > > > >  */
> > > > > 
> > > > > idr_alloc is a very simple wrapper around idr_alloc_u32().
> > > > > 
> > > > > On top of radix_tree_node_alloc() which is called by idr_alloc_u32(), there is
> > > > > this comment at line 244 in the same radix-tree.c
> > > > > /*
> > > > >  * This assumes that the caller has performed appropriate preallocation, and
> > > > >  * that the caller has pinned this thread of control to the current CPU.
> > > > >  */
> > > > > 
> > > > > Therefore the preload/preload_end are necessary, or at least should have
> > > > > preemption disabled
> > > > 
> > > > Ah, so it's disabling preemption that is the key here.  Still odd, why
> > > > is GFP_ATOMIC not sufficient in a normal idr_alloc() call to keep things
> > > > from doing stuff like this?  Feels like a lot of "internal knowledge" is
> > > > needed here to use this api properly...
> > > > 
> > > > Matthew, is the above change really correct?
> > > 
> > > No.
> > > 
> > > https://lore.kernel.org/netdev/20200605112922.GB19604@bombadil.infradead.org/
> > > https://lore.kernel.org/netdev/20200605120037.17427-1-willy@infradead.org/
> > > https://lore.kernel.org/netdev/20200914192655.GW6583@casper.infradead.org/
> > > 
> > 
> > Ok, it looks like this code is just abandonded, should we remove it
> > entirely as no one wants to maintain it?
> 
> Fine by me.  I don't use it.  Better to get rid of abandonware than keep
> a potential source of security holes.

Hi Manivannan,

For your information.

Regards,
Du Cheng

Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

[Manivannan Sadhasivam]

On Mon, Mar 29, 2021 at 06:55:56PM +0800, Du Cheng wrote:
> On Sun, Mar 28, 2021 at 11:04:17AM +0100, Matthew Wilcox wrote:
> > On Sun, Mar 28, 2021 at 08:56:17AM +0200, Greg Kroah-Hartman wrote:
> > > On Sat, Mar 27, 2021 at 03:51:10PM +0000, Matthew Wilcox wrote:
> > > > On Sat, Mar 27, 2021 at 03:31:18PM +0100, Greg Kroah-Hartman wrote:
> > > > > On Sat, Mar 27, 2021 at 10:25:20PM +0800, Du Cheng wrote:
> > > > > > On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote:
> > > > > > > Adding the xarray maintainer...
> > > > > > > 
> > > > > > > On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> > > > > > > > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> > > > > > > > due to internal use of per_cpu variables, which requires preemption
> > > > > > > > disabling/enabling.
> > > > > > > > 
> > > > > > > > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> > > > > > > > 
> > > > > > > > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> > > > > > > > Signed-off-by: Du Cheng <ducheng2@gmail.com>
> > > > > > > > ---
> > > > > > > > changelog
> > > > > > > > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> > > > > > > > v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> > > > > > > > 
> > > > > > > >  net/qrtr/qrtr.c | 6 ++++++
> > > > > > > >  1 file changed, 6 insertions(+)
> > > > > > > > 
> > > > > > > > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> > > > > > > > index edb6ac17ceca..6361f169490e 100644
> > > > > > > > --- a/net/qrtr/qrtr.c
> > > > > > > > +++ b/net/qrtr/qrtr.c
> > > > > > > > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> > > > > > > >  	mutex_lock(&qrtr_port_lock);
> > > > > > > >  	if (!*port) {
> > > > > > > >  		min_port = QRTR_MIN_EPH_SOCKET;
> > > > > > > > +		idr_preload(GFP_ATOMIC);
> > > > > > > >  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> > > > > > > > +		idr_preload_end();
> > > > > > > 

[...]

> > > Ok, it looks like this code is just abandonded, should we remove it
> > > entirely as no one wants to maintain it?
> > 
> > Fine by me.  I don't use it.  Better to get rid of abandonware than keep
> > a potential source of security holes.
> 
> Hi Manivannan,
> 
> For your information.
> 

Thanks for letting me know. I'll look into it once back to work.

Thanks,
Mani

> Regards,
> Du Cheng