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[34.76.69.250]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4923fd15535sm497130755e9.3.2026.06.24.06.54.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jun 2026 06:54:29 -0700 (PDT) From: David Maximiliano Hermitte To: Viacheslav Dubeyko , Jori Koolstra Cc: John Paul Adrian Glaubitz , Yangtao Li , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+97e301b4b82ae803d21b@syzkaller.appspotmail.com, David Maximiliano Hermitte Subject: Re: [PATCH v2] hfs: validate corrupt catalog and btree metadata before hfs_write_inode() Date: Wed, 24 Jun 2026 13:54:12 +0000 Message-ID: <20260624135412.7208-1-davemadmaxxx@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hello Slava, Jori, all, I am following up with a refined test patch for the same HFS syzbot reproducer. This variant does not change hfs_write_inode(), hfs_test_inode(), or the BUG() site. It rejects corrupted catalog/B-tree metadata earlier: - hfs_brec_read(): rejects invalid entry offset/length, caches node_size locally, and uses overflow-safe bounds arithmetic. - hfs_read_inode(): rejects invalid file/directory CNIDs before writeback. Local validation on commit 840ef6c78e6a: - git diff --check: pass - checkpatch.pl --strict: 0 errors, 0 warnings - make -j2 fs/hfs/: pass - bzImage built - QEMU/TCG with the same public syzbot ReproC: - BEFORE: repro_started=true, kernel_bug_seen=true - AFTER: repro_started=true, repro_done=true, kernel_bug_seen=false, hfs_write_inode_seen=false, kasan_seen=false, oops_seen=false - verdict=REPRO_RAN_NO_BUG_SEEN I have prepared this refined variant because the hfs_brec_read() bounds check now validates entryoffset before computing node_size - entryoffset, caches node_size locally, and rejects entryoffset >= node_size explicitly. I am including it inline because it avoids potential integer overflow in the bounds check while preserving the same QEMU validation result. I am sending it as a test patch / direction check, not as a final maintainer-ready fix. The point is that validating corrupt catalog/B-tree metadata before hfs_write_inode() prevents this reproducer from reaching the BUG() endpoint. I would appreciate your opinion on whether this placement/direction is closer to the expected HFS fix. Best regards, David Patch follows: diff --git a/fs/hfs/bfind.c b/fs/hfs/bfind.c index d56e47bdc517..e48a7110e342 100644 --- a/fs/hfs/bfind.c +++ b/fs/hfs/bfind.c @@ -170,12 +170,20 @@ int hfs_brec_find(struct hfs_find_data *fd) int hfs_brec_read(struct hfs_find_data *fd, void *rec, u32 rec_len) { int res; + u32 node_size; res = hfs_brec_find(fd); if (res) return res; + node_size = fd->bnode->tree->node_size; + if (fd->entryoffset < 0 || fd->entrylength <= 0) + return -EFSCORRUPTED; + if (fd->entryoffset >= node_size) + return -EFSCORRUPTED; + if (fd->entrylength > node_size - fd->entryoffset) + return -EFSCORRUPTED; if (fd->entrylength > rec_len) - return -EINVAL; + return -EFSCORRUPTED; hfs_bnode_read(fd->bnode, rec, fd->entryoffset, fd->entrylength); return 0; } diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c index ac4a9055c5c0..7283b9541064 100644 --- a/fs/hfs/inode.c +++ b/fs/hfs/inode.c @@ -367,6 +367,9 @@ static int hfs_read_inode(struct inode *inode, void *data) rec = idata->rec; switch (rec->type) { case HFS_CDR_FIL: + /* Reject corrupted user file CNIDs before writeback. */ + if (be32_to_cpu(rec->file.FlNum) < HFS_FIRSTUSER_CNID) + return -EFSCORRUPTED; if (!HFS_IS_RSRC(inode)) { hfs_inode_read_fork(inode, rec->file.ExtRec, rec->file.LgLen, rec->file.PyLen, be16_to_cpu(rec->file.ClpSize)); @@ -390,6 +393,10 @@ static int hfs_read_inode(struct inode *inode, void *data) inode->i_mapping->a_ops = &hfs_aops; break; case HFS_CDR_DIR: + /* Only the root directory may use a reserved CNID here. */ + if (be32_to_cpu(rec->dir.DirID) < HFS_FIRSTUSER_CNID && + be32_to_cpu(rec->dir.DirID) != HFS_ROOT_CNID) + return -EFSCORRUPTED; inode->i_ino = be32_to_cpu(rec->dir.DirID); inode->i_size = be16_to_cpu(rec->dir.Val) + 2; HFS_I(inode)->fs_blocks = 0;