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Fri, 16 Jun 2023 23:18:09 -0700 (PDT) MIME-Version: 1.0 References: <20230617044036.3985524-1-zhiguangni01@gmail.com> <20230616224407.863c74a3dc9d4f1427802f91@linux-foundation.org> In-Reply-To: <20230616224407.863c74a3dc9d4f1427802f91@linux-foundation.org> From: Liam Ni Date: Sat, 17 Jun 2023 14:17:58 +0800 Message-ID: Subject: Re: [PATCH] mm/sparse:avoid null pointer access in memory_present() To: Andrew Morton Cc: dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, rppt@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: xeh5aohuyqmd7e7puon1sasw9a7ioyc7 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 05BF210000E X-HE-Tag: 1686982689-788074 X-HE-Meta: U2FsdGVkX1/LuBY34y+/8b55iU+TCssuSZ+eQH/vPDDc2FeYAZaDyq1F69ad40b/GrK1ln54H34vV8fitr+8d3H/1749Q+ux6qYeQHDTN/AzDw8/ECTIoxmwBB+DTeoJWh7xE3bUj+bHAkTcK88rpNidITlALqvJJwpt0UFD2Z1HZIbyhEfOXFIpJvXYa5gwhSGN4xcPeOwMQvUyWjjw+kdFXZIyq3utalbrxvB0RKuxpLVVB1NTpJdddp/OTWEy4ICNlivMoRT2hmv6T1GPN1J111sWUJz/2Tvb3O+d49MEP6OgbHPTSNTkPnM9uBhfFQ9LpZFJieWlfEs+AhVvk/7mWCRtEqpH+50EIqooWTn4xkW8WKL7pqgTMhFv34iVIA+KgoekoEPVRl1p2CO0GYRIHGKla3ZHE+eWCFEXaSgxSS3oSwH11RGMQNaBEDloWU8JExYwjjJ1XcPBQCz5zwVCTAQyhGyw5RCLHM+Uv2BAEtBLKt0NAYH+qjRx9Rxxx8IryUg3ala26O5REphlk3Hn7Mwy0NL7tvoTf+lvRGhDvdK7f7iNgfgGYn4TAgM3y1CxPZ0yOK83Fd7CrpREZ1frzt1py7dCLYayE3ciUXg2y4gJlq7UD4r/G72NS/rJH54zKlKxtBGJgtrnJ6iBtfQSxCpUmvIF+jWMHS7xpwg1IoMeFRKstRrI84ETem7ka2RoR+LjL1EXYc3WipGVfnRpDmoeizuPigdLVm7zl+BfKM0wdYE+/DAPQQZcdHl0pyhpZlD39+adZ+3lf4Hl7uVNqDjZTzshmPoyZBLdAa+Jv8JHjEjP5fl2E/BlYqj27ThTktGIfVzgLRXDBPDamcaCoy6XffQjMgesswIgGHBAIyDQIBbagAnlI/V2GGsyjm+tdipXZ4T67gV3CeQJteAhAt7Z3r+nVROjIyghPoxoKrtAnDNKadHkINN5vSjqfG7Csv7PZ3zvhusWvmq eDMTLqXT LkfsH/rg+LdtfCLMEEvyI+VtVwh2Q0W5hJ6YANDC8F4uX1YMeOFc9yi3u94oYJHr7TL76nW+1cBRc6mrY5Dcdd8lNByNwzIfWQSqy1CnyyJ3pgyR0ToZ6iGqPwbrXMR3R7qsuzjagOtKCIii2+YVlo+FN0J+ITvCrVVWLyTYwjiOxGRVsYH4zFhdb4fjmYKnOL0bTKo3prlezM0WysIZYiTa+1DEU+NYgBF9Z2BzYuLDlJdfKf2LF5j3CLelDoyZgGOQ+fZfdzRsxhK3SrT1xSloHFo2l1x+7mdqpslBnNjCPkHh465u4fs3W5ZakTpS4/Eeae9heHqVpcP+gQc6u97kjEw+3RoscURJGJ5fLPtmbfGbBuUFbLYu1yF+0v/ZB8Q71lDsK641sSIjxCY1IiU4SI7eVi+k4ztTLc3OYSwaKoxa4EAHeXNxriqgd4c+87mrdgy2xdOPF2kEjeuRnnhy/BD1nnMO8/LvZY8OrGkKAgGY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, 17 Jun 2023 at 13:44, Andrew Morton wro= te: > > On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni wrote= : > > > __nr_to_section() may return a null pointer, > > before accessing the member variable section_mem_map, > > we should first determine whether it is a null pointer. > > > > ... > > > > --- a/mm/sparse.c > > +++ b/mm/sparse.c > > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned= long start, unsigned long en > > set_section_nid(section, nid); > > > > ms =3D __nr_to_section(section); > > - if (!ms->section_mem_map) { > > + if (ms && !ms->section_mem_map) { > > ms->section_mem_map =3D sparse_encode_early_nid(n= id) | > > SECTION_IS_ONLINE= ; > > __section_mark_present(ms, section); > > I'm suspecting that if __nr_to_section() returns NULL here, we should > just panic. But a null-deref gives the same information, so why change > things? Do you mean if ms is a null pointer=EF=BC=8Cms->section_mem_map will cause system panic,so we needn't change? >