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b=ZzuHD4GfgdAkX+OUfQZ6s7tIgAQjGqlqG7OhOna8OhvbMDSeHf6VeKfOHVcSh4/tm 8XIBmh7+Vx7lTluK+P8eFyYsACVvqdN4LsDY+JRyF+2WvXMocelVF+MBLGwxj3HUmE tKi+7G74HzQEWKKQQ1Duf93OfrGeAiWU9A2MfKgNPir+AR/wFXQ1mwAF00nZpV7674 2tELmsn+Tn/7ooLIyS4NPUHqZwOaHCptdW68CGWV1EWC50i6yX7sjcech7zZY4Onpm UfjrFl+wjzhmL5Kh261xy7QdpWy10OiAZ708xw1p9jqE5xAJ4nCdpAu9KWJry3mpRZ tCaljRNJprcWg== From: sashiko-bot@kernel.org Subject: Re: [RFC PATCH 4/6] mm/memfd_luo: allow preserving a tmpfs mount Reply-To: sashiko-reviews@lists.linux.dev To: "Baolin Wang" , "Hugh Dickins" , "Mike Rapoport" , "Pratyush Yadav" , "Samiullah Khawaja" , "Alexander Graf" , "David Matlack" , "Pasha Tatashin" , "Andrew Morton" , "David Hildenbrand" , "Lorenzo Stoakes" Cc: kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org In-Reply-To: <20260923224408.3745689-5-pratyush@kernel.org> References: <20260923224408.3745689-1-pratyush@kernel.org> <20260923224408.3745689-5-pratyush@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Wed, 23 Sep 2026 23:06:44 +0000 Message-Id: <20260923230644.E847A1F000FF@smtp.kernel.org> X-Rspamd-Queue-Id: 9032E18000D X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: g71x6sgywcxgkiofdxr55rydm9mfh4tj X-HE-Tag: 1790204806-930884 X-HE-Meta: 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 nO7YzmPP CsFUZdcMvdZ/eL/sVVX3ye4sSZEG9zdnfWrpkf+s0mcib2+YJ5QmHN4SuPZG+ZWjOFXqVBMserta4VF6VrTDbo7L1dQ6jkHjUCDZElRr+s9iXrxTgPOk59D6QBmqoqkYeZvdBCxCeoWME3oVWY8KU4JRsJhO+uHUh01tHBaITa8yI8suVBJ3ck1+GOW2hplZc4GPW/BY2QAPQ4b31fVRMnXM/GRMhySGj9RJNs3kuelMyY1NN0mkeLGSbYLBVYzfpaIsYeMaj6A6yk1KRzeqt3suvknhE2W6pGSpT1zBjrBamJxuDL0tLlQi4MEJbNI8y9AH0BG3H/POJovF+3qMncouko4EOKKdGs79YyV1jbdsoyTRHAex9MwQyfrzpz25Mpw2YgCAR+ic50S4TPNskpZSJQur7SS2h33h7wlsolBY7Qhau27cq8IKrs1SYN2cuO+4Z7O87QaWV2ONugBVyjk8UG9/z6tdqRMJJ7q1sLZjWHP8inxGJ8BVw9fG2eZFw/sBGilTC9IeBk9D/6ht0AGPrFF28R06phQOk+fnxm/VfvN3QX6J/XsTwuqCu1mesTM28G1SVRkkiUPmSQBKnrBzolRJmJqHTQ6IVJgT7km/IqCkew/6KBXXS+4hsSzchprpuxFcfFhLmp88= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Thank you for your contribution! Sashiko AI review found 2 potential issue(= s) to consider: - [Medium] mm: tmpfs LUO drops group quotas due to incomplete USRQUOTA check - [Medium] mm: TOCTOU race allows unsupported ID mappings and quotas to byp= ass LUO validation -- commit 20e62ff0b162f0ffc76cd0d972cc6c760a83d003 Author: Pratyush Yadav (Google) mm/memfd_luo: allow preserving a tmpfs mount This commit adds support for preserving a tmpfs mount across a live update. It preserves the filesystem block limit and root directory mode, while resetting other options to default, identifying the mount via a file pointing to it. > diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c > --- a/mm/memfd_luo.c > +++ b/mm/memfd_luo.c [ ... ] > +static bool tmpfs_luo_mnt_can_preserve(struct liveupdate_file_handler *f= h, > + struct file *file) > +{ [ ... ] > + /* These features are not supported. */ > + if (SHMEM_SB(sb)->mpol || sb_has_quota_active(sb, USRQUOTA) || > + sb_has_encoding(sb) || is_idmapped_mnt(mnt)) > + return false; [Severity: Medium] Does this condition improperly accept tmpfs mounts with group or project quotas active?=20 The check only tests for USRQUOTA, which means mounts with grpquota or=20 prjquota will bypass this rejection and their quota state will be silently lost across kexec.=20 Should this use sb_any_quota_loaded(sb) to properly detect all quota types? [ ... ] > +static int tmpfs_luo_mnt_freeze(struct liveupdate_file_op_args *args) > +{ > + struct super_block *sb =3D args->file->f_path.mnt->mnt_sb; > + struct shmem_sb_info *sbinfo =3D SHMEM_SB(sb); > + struct tmpfs_luo_mnt_ser *ser; > + > + /* > + * A remount can install a memory policy after can_preserve() accepted > + * the mount. > + */ > + if (sbinfo->mpol) > + return -EOPNOTSUPP; [Severity: Medium] Does this leave a TOCTOU window for ID mappings and quotas?=20 While mpol is re-validated here to handle concurrent remounts, checks for is_idmapped_mnt() and quotas are missing. If a user concurrently adds an ID mapping via mount_setattr() or enables quotas via remount after the tmpfs_luo_mnt_can_preserve() check passes, those unsupported properties will bypass validation and be silently dropped across kexec. Should this re-validate the ID mapping and quota state as well? --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260923224408.3745= 689-1-pratyush@kernel.org?part=3D4