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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-877a9b18689sm1299910b3a.40.2026.09.19.13.48.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 13:48:11 -0700 (PDT) From: Hui Peng To: OGAWA Hirofumi Cc: Jan Kara , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] fat: avoid freeing clusters on failed directory validation or read-only mounts Date: Sat, 19 Sep 2026 20:48:10 +0000 Message-ID: <20260919204810.2813594-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In fat_fill_inode(), set_nlink(inode, fat_subdirs(inode)) is called before fat_validate_dir(inode). If a directory has zero valid subdirectories (so fat_subdirs(inode) returns 0) and fat_validate_dir() subsequently returns -EIO (due to a missing or malformed '.'/'..' entry), fat_build_inode() calls iput(inode) with inode->i_nlink == 0 and inode->i_start still populated. fat_evict_inode() then checks !inode->i_nlink without checking is_bad_inode(inode) or sb_rdonly(inode->i_sb) and calls fat_truncate_blocks(inode, 0), freeing the cluster chain on disk even on a read-only (MS_RDONLY) mount. Validate the directory before setting i_nlink in fat_fill_inode(), mark the inode bad on error in fat_build_inode(), and guard cluster truncation and metadata writeback in fat_evict_inode() with !is_bad_inode(inode) && !sb_rdonly(inode->i_sb). Fixes: a3082d526f2d ("fat: add simple validation for directory inode") Assisted-by: LLM Signed-off-by: Hui Peng --- diff --git a/fs/fat/inode.c b/fs/fat/inode.c --- a/fs/fat/inode.c +++ b/fs/fat/inode.c @@ -535,11 +535,11 @@ int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de) return error; MSDOS_I(inode)->mmu_private = inode->i_size; - set_nlink(inode, fat_subdirs(inode)); - error = fat_validate_dir(inode); if (error < 0) return error; + + set_nlink(inode, fat_subdirs(inode)); } else { /* not a directory */ inode->i_generation |= 1; inode->i_mode = fat_make_mode(sbi, de->attr, @@ -610,6 +610,7 @@ struct inode *fat_build_inode(struct super_block *sb, inode_set_iversion(inode, 1); err = fat_fill_inode(inode, de); if (err) { + make_bad_inode(inode); iput(inode); inode = ERR_PTR(err); goto out; @@ -688,12 +689,14 @@ static void fat_free_eofblocks(struct inode *inode) static void fat_evict_inode(struct inode *inode) { truncate_inode_pages_final(&inode->i_data); - if (!inode->i_nlink) { - inode->i_size = 0; - fat_truncate_blocks(inode, 0); - } else { - mmb_sync(&MSDOS_I(inode)->i_metadata_bhs); - fat_free_eofblocks(inode); + if (!is_bad_inode(inode) && !sb_rdonly(inode->i_sb)) { + if (!inode->i_nlink) { + inode->i_size = 0; + fat_truncate_blocks(inode, 0); + } else { + mmb_sync(&MSDOS_I(inode)->i_metadata_bhs); + fat_free_eofblocks(inode); + } } mmb_invalidate(&MSDOS_I(inode)->i_metadata_bhs); -- 2.43.0