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b=JCOnoye0iRgKQ2/Hkv1xCXmCs2iJwfAE1Iz4Pqv08JDL6zWTRDdATiNeJxSkbuLkm W6VhgwYWT7ONxhf84Ljf0iLwP7DW1oQlpPb/jApYhZnkWrc5Fzbi/HNFm+nG6l94QS whi9KTK2GaDC+9dWJbW8oAkDX0oKwUylyZ+4kAkhxhMbToBfPqBKqY2pfjzLTT9+lX qLJnwF9xzMLjTvtYQQa6/bly0eDxYL4BN/oayNeNYxAUfjBwI/t3mnbEJ447sJAmig 2oTUoFUJtYXtcEEipxpCK8my4F2x5LBZpqF+aWz57JsAPhc2tP6+K77IJL+ceD2das GqeDo9nQG9e5g== From: SeongJae Park To: SeongJae Park Cc: Josh Law , Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: (sashiko review) [PATCH] mm/damon/core: validate goal nid before accessing node data Date: Wed, 25 Mar 2026 08:04:10 -0700 Message-ID: <20260325150411.88357-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260325143740.87690-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 5BFE6120011 X-Stat-Signature: 4y6zbwztxne3fpyjaoqgeh64mp44f3an X-Rspam-User: X-HE-Tag: 1774451059-186457 X-HE-Meta: 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 dxWtnmkh DsU5tVwUeRIFyjPIh13lHSWwvKo11ej1NG7KuEzhYLDLZx5F18sRvcVDSye4LrnvCSg6Slp1NRkoNPseIlyUjiS0VI1t/9/uf+PRQ8M09W/bL0Oh2AnI6UqSLWfhZebX95oI/IoLI2tgdfBwzH+4BhW40ciUlSHGdNoSYatnxaiGQNKy94fXBBpcfuC+2tepNSS4xiRnS6/5xvuZmNDD+p/FIHO7Ma4osSX6wAo/ffMzpOTwaCiq0sUZXPU9xxjpap87tNnvCSGO01xUG6swvJXAvE8ma/zmy4MJT3Gwc4vLcILk/AAi8FDrDHXBH4g58EXt/VUNo3ZAwSwxjKTxPErY6RwmHh/XJiqpP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 25 Mar 2026 07:37:39 -0700 SeongJae Park wrote: > Forwarding Sashiko review for doing discussions via mails. > > # review url: https://sashiko.dev/#/patchset/20260325073034.140353-1-objecting@objecting.org > # start of sashiko.dev inline review > commit 7e17cbe1dc95a0cd1a1410be38ab6964f78fb15c > Author: Josh Law > > mm/damon/core: validate goal nid before accessing node data > > This commit adds bounds checking and node_online() validation for the > goal->nid in the DAMON quota metrics. It prevents out-of-bounds accesses > to NODE_DATA() when an invalid or offline NUMA node is provided by userspace. > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > index db6c67e52d2b..81ce27baa1a1 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_online(goal->nid)) > > + return 0; > > + > > 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); > > Could this cause a division by zero if the node is online but memoryless? > > For CPU-only compute nodes or nodes where all memory has been hot-removed, > node_online(goal->nid) will evaluate to true. When si_meminfo_node() is > called for these memoryless nodes, it populates the sysinfo struct with > i.totalram = 0. > > The mult_frac() macro unconditionally performs integer division and modulo > by the third argument, which could trigger a kernel panic when dividing by > zero. > > Would it be safer to check if i.totalram is zero before returning, or use > node_state(goal->nid, N_MEMORY) instead of node_online()? > > [ ... ] > > > @@ -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_online(goal->nid)) > > + return 0; > > + > > memcg = mem_cgroup_get_from_id(goal->memcg_id); > > The same division by zero risk exists here when mult_frac() is called at the > end of this function. I think sashiko's comments make sense. I also suggested using node_state(N_MEMORY). What do you think, Josh? Thanks, SJ [...]