[PATCH v2] mm/damon/core: validate goal nid before accessing node data

[PATCH v2] mm/damon/core: validate goal nid before accessing node data

[Josh Law]

damos_get_node_mem_bp() and damos_get_node_memcg_used_bp() pass
goal->nid directly to si_meminfo_node() and NODE_DATA() without
checking that it refers to a valid, online NUMA node.  Since
goal->nid is set from userspace via sysfs with no validation, a
negative or out-of-range value causes an out-of-bounds access in
NODE_DATA(), and a valid but offline node gives undefined results.

Add bounds and node_state(N_MEMORY) checks before using the nid,
consistent with damon_migrate_pages().

Fixes: 0e1c773b501f ("mm/damon/core: introduce damos quota goal metrics for memory node utilization")
Cc: stable@vger.kernel.org
Signed-off-by: Josh Law <objecting@objecting.org>
---
 mm/damon/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 59b709f04975..112125b635d7 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2227,6 +2227,10 @@ static __kernel_ulong_t damos_get_node_mem_bp(
 	struct sysinfo i;
 	__kernel_ulong_t numerator;
 
+	if (goal->nid < 0 || goal->nid >= MAX_NUMNODES ||
+	    !node_state(goal->nid, N_MEMORY))
+		return 0;
+
 	si_meminfo_node(&i, goal->nid);
 	if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP)
 		numerator = i.totalram - i.freeram;
@@ -2243,6 +2247,10 @@ static unsigned long damos_get_node_memcg_used_bp(
 	unsigned long used_pages, numerator;
 	struct sysinfo i;
 
+	if (goal->nid < 0 || goal->nid >= MAX_NUMNODES ||
+	    !node_state(goal->nid, N_MEMORY))
+		return 0;
+
 	memcg = mem_cgroup_get_from_id(goal->memcg_id);
 	if (!memcg) {
 		if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP)
-- 
2.34.1

Re: (sashiko review) [PATCH v2] mm/damon/core: validate goal nid before accessing node data

[SeongJae Park]

Forwarding Sashiko review for doing discussions via mails.

# review url: https://sashiko.dev/#/patchset/20260325155221.202700-1-objecting@objecting.org
# start of sashiko.dev inline review
commit 24e25058b8f508495d0b3db33bed16564df7fed4
Author: Josh Law <objecting@objecting.org>
Subject: mm/damon/core: validate goal nid before accessing node data

This patch adds bounds and node_state(N_MEMORY) checks before using
goal->nid from userspace to prevent out-of-bounds access in NODE_DATA().

Cc: stable@vger.kernel.org

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index db6c67e52d2b..ed45a7443abe 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2245,6 +2245,10 @@ static __kernel_ulong_t damos_get_node_mem_bp(
>  	struct sysinfo i;
>  	__kernel_ulong_t numerator;
>  
> +	if (goal->nid < 0 || goal->nid >= MAX_NUMNODES ||
> +	    !node_state(goal->nid, N_MEMORY))
> +		return 0;
> +

When goal->nid is invalid or offline, this unconditionally returns 0.
For the DAMOS_QUOTA_NODE_MEM_FREE_BP metric, wouldn't returning 0 imply
0% free memory?

Could this cause the DAMON feedback loop to interpret the goal as
severely under-achieved and drastically increase the scheme's
aggressiveness?

Should this fallback logic check the metric type and return 10000
(100% free) for FREE_BP metrics to fail gracefully, mirroring the
existing fallback logic used when a memory cgroup lookup fails?

>  	si_meminfo_node(&i, goal->nid);
>  	if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP)
>  		numerator = i.totalram - i.freeram;
>  	else	/* DAMOS_QUOTA_NODE_MEM_FREE_BP */
>  		numerator = i.freeram;
>  	return mult_frac(numerator, 10000, i.totalram);

While not introduced by this patch, since this function is being
modified to handle node edge cases, is it possible for a node to have
N_MEMORY set, but have 0 managed pages? For example, if all of its
memory is reserved for hugetlb or unmanaged ZONE_DEVICE memory.

If so, si_meminfo_node() would set i.totalram to 0. Would the call
to mult_frac() then cause a divide-by-zero panic when it evaluates
x_ / d_ ?

> @@ -2261,6 +2265,10 @@ static unsigned long damos_get_node_memcg_used_bp(
>  	unsigned long used_pages, numerator;
>  	struct sysinfo i;
>  
> +	if (goal->nid < 0 || goal->nid >= MAX_NUMNODES ||
> +	    !node_state(goal->nid, N_MEMORY))
> +		return 0;
> +

Similar to the function above, returning 0 unconditionally here for
DAMOS_QUOTA_NODE_MEMCG_FREE_BP might artificially trigger maximum
reclaim aggressiveness.


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Re: [PATCH v2] mm/damon/core: validate goal nid before accessing node data

[SeongJae Park]

On Wed, 25 Mar 2026 15:52:21 +0000 Josh Law <objecting@objecting.org> wrote:

No rush, Josh.  As I mentioned before, please give about a day after the last
comment on the previous version of the patch, before posting a new version.
That could help giving enough time for others to add their important findings.

> damos_get_node_mem_bp() and damos_get_node_memcg_used_bp() pass
> goal->nid directly to si_meminfo_node() and NODE_DATA() without
> checking that it refers to a valid, online NUMA node.  Since

s/online/memory/ ?

> goal->nid is set from userspace via sysfs with no validation, a
> negative or out-of-range value causes an out-of-bounds access in
> NODE_DATA(), and a valid but offline node gives undefined results.
> 
> Add bounds and node_state(N_MEMORY) checks before using the nid,
> consistent with damon_migrate_pages().
> 
> Fixes: 0e1c773b501f ("mm/damon/core: introduce damos quota goal metrics for memory node utilization")
> Cc: stable@vger.kernel.org
> Signed-off-by: Josh Law <objecting@objecting.org>
> ---

As I also previously mentioned, please add changelog here.

>  mm/damon/core.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 59b709f04975..112125b635d7 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2227,6 +2227,10 @@ static __kernel_ulong_t damos_get_node_mem_bp(
>  	struct sysinfo i;
>  	__kernel_ulong_t numerator;
>  
> +	if (goal->nid < 0 || goal->nid >= MAX_NUMNODES ||
> +	    !node_state(goal->nid, N_MEMORY))
> +		return 0;
> +
>  	si_meminfo_node(&i, goal->nid);
>  	if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP)
>  		numerator = i.totalram - i.freeram;
> @@ -2243,6 +2247,10 @@ static unsigned long damos_get_node_memcg_used_bp(
>  	unsigned long used_pages, numerator;
>  	struct sysinfo i;
>  
> +	if (goal->nid < 0 || goal->nid >= MAX_NUMNODES ||
> +	    !node_state(goal->nid, N_MEMORY))
> +		return 0;
> +
>  	memcg = mem_cgroup_get_from_id(goal->memcg_id);
>  	if (!memcg) {
>  		if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP)
> -- 
> 2.34.1

I will add more comments as a reply to sashiko comment.


Thanks,
SJ

[...]

Re: (sashiko review) [PATCH v2] mm/damon/core: validate goal nid before accessing node data

[SeongJae Park]

On Wed, 25 Mar 2026 17:10:50 -0700 SeongJae Park <sj@kernel.org> wrote:

> Forwarding Sashiko review for doing discussions via mails.
> 
> # review url: https://sashiko.dev/#/patchset/20260325155221.202700-1-objecting@objecting.org
> # start of sashiko.dev inline review
> commit 24e25058b8f508495d0b3db33bed16564df7fed4
> Author: Josh Law <objecting@objecting.org>
> Subject: mm/damon/core: validate goal nid before accessing node data
> 
> This patch adds bounds and node_state(N_MEMORY) checks before using
> goal->nid from userspace to prevent out-of-bounds access in NODE_DATA().
> 
> Cc: stable@vger.kernel.org
> 
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index db6c67e52d2b..ed45a7443abe 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -2245,6 +2245,10 @@ static __kernel_ulong_t damos_get_node_mem_bp(
> >  	struct sysinfo i;
> >  	__kernel_ulong_t numerator;
> >  
> > +	if (goal->nid < 0 || goal->nid >= MAX_NUMNODES ||
> > +	    !node_state(goal->nid, N_MEMORY))
> > +		return 0;
> > +
> 
> When goal->nid is invalid or offline, this unconditionally returns 0.
> For the DAMOS_QUOTA_NODE_MEM_FREE_BP metric, wouldn't returning 0 imply
> 0% free memory?
> 
> Could this cause the DAMON feedback loop to interpret the goal as
> severely under-achieved and drastically increase the scheme's
> aggressiveness?
> 
> Should this fallback logic check the metric type and return 10000
> (100% free) for FREE_BP metrics to fail gracefully, mirroring the
> existing fallback logic used when a memory cgroup lookup fails?

I am also thinking similar to sashiko.  Could you please make the change?

> 
> >  	si_meminfo_node(&i, goal->nid);
> >  	if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP)
> >  		numerator = i.totalram - i.freeram;
> >  	else	/* DAMOS_QUOTA_NODE_MEM_FREE_BP */
> >  		numerator = i.freeram;
> >  	return mult_frac(numerator, 10000, i.totalram);
> 
> While not introduced by this patch, since this function is being
> modified to handle node edge cases, is it possible for a node to have
> N_MEMORY set, but have 0 managed pages? For example, if all of its
> memory is reserved for hugetlb or unmanaged ZONE_DEVICE memory.

I'm not very sure if this is really possible.  Josh, do you know?

> 
> If so, si_meminfo_node() would set i.totalram to 0. Would the call
> to mult_frac() then cause a divide-by-zero panic when it evaluates
> x_ / d_ ?

If sashiko's theory is true, I think we should add a zero value check here?

> 
> > @@ -2261,6 +2265,10 @@ static unsigned long damos_get_node_memcg_used_bp(
> >  	unsigned long used_pages, numerator;
> >  	struct sysinfo i;
> >  
> > +	if (goal->nid < 0 || goal->nid >= MAX_NUMNODES ||
> > +	    !node_state(goal->nid, N_MEMORY))
> > +		return 0;
> > +
> 
> Similar to the function above, returning 0 unconditionally here for
> DAMOS_QUOTA_NODE_MEMCG_FREE_BP might artificially trigger maximum
> reclaim aggressiveness.

Similar to my above comment, I agree to sashiko.


Thanks,
SJ

[...]