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([2600:1700:6476:1430:7c1e:d951:252e:7fc3]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-66c7934afe7sm323119d50.15.2026.08.13.21.19.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Aug 2026 21:19:27 -0700 (PDT) Message-ID: <6d076dc1b4f0925f1beaeca7cebcf3752a19aa0f.camel@dubeyko.com> Subject: Re: [PATCH 2/2] hfs/hfsplus: stop btree allocators from reusing node 0 From: Viacheslav Dubeyko To: Tao Yu , linux-fsdevel@vger.kernel.org Cc: glaubitz@physik.fu-berlin.de, frank.li@vivo.com, linux-kernel@vger.kernel.org, syzbot+2bf21610eea63cb2ce93@syzkaller.appspotmail.com Date: Thu, 13 Aug 2026 21:19:22 -0700 In-Reply-To: <20260814023150.3482810-3-tao1.yu@intel.com> References: <20260814023150.3482810-1-tao1.yu@intel.com> <20260814023150.3482810-3-tao1.yu@intel.com> Autocrypt: addr=slava@dubeyko.com; prefer-encrypt=mutual; keydata=mQINBGgaTLYBEADaJc/WqWTeunGetXyyGJ5Za7b23M/ozuDCWCp+yWUa2GqQKH40dxRIR zshgOmAue7t9RQJU9lxZ4ZHWbi1Hzz85+0omefEdAKFmxTO6+CYV0g/sapU0wPJws3sC2Pbda9/eJ ZcvScAX2n/PlhpTnzJKf3JkHh3nM1ACO3jzSe2/muSQJvqMLG2D71ccekr1RyUh8V+OZdrPtfkDam V6GOT6IvyE+d+55fzmo20nJKecvbyvdikWwZvjjCENsG9qOf3TcCJ9DDYwjyYe1To8b+mQM9nHcxp jUsUuH074BhISFwt99/htZdSgp4csiGeXr8f9BEotRB6+kjMBHaiJ6B7BIlDmlffyR4f3oR/5hxgy dvIxMocqyc03xVyM6tA4ZrshKkwDgZIFEKkx37ec22ZJczNwGywKQW2TGXUTZVbdooiG4tXbRBLxe ga/NTZ52ZdEkSxAUGw/l0y0InTtdDIWvfUT+WXtQcEPRBE6HHhoeFehLzWL/o7w5Hog+0hXhNjqte fzKpI2fWmYzoIb6ueNmE/8sP9fWXo6Av9m8B5hRvF/hVWfEysr/2LSqN+xjt9NEbg8WNRMLy/Y0MS p5fgf9pmGF78waFiBvgZIQNuQnHrM+0BmYOhR0JKoHjt7r5wLyNiKFc8b7xXndyCDYfniO3ljbr0j tXWRGxx4to6FwARAQABtCZWaWFjaGVzbGF2IER1YmV5a28gPHNsYXZhQGR1YmV5a28uY29tPokCVw QTAQoAQQIbAQUJA8JnAAULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBFXDC2tnzsoLQtrbBDlc2cL fhEB1BQJoGl5PAhkBAAoJEDlc2cLfhEB17DsP/jy/Dx19MtxWOniPqpQf2s65enkDZuMIQ94jSg7B F2qTKIbNR9SmsczjyjC+/J7m7WZRmcqnwFYMOyNfh12aF2WhjT7p5xEAbvfGVYwUpUrg/lcacdT0D Yk61GGc5ZB89OAWHLr0FJjI54bd7kn7E/JRQF4dqNsxU8qcPXQ0wLHxTHUPZu/w5Zu/cO+lQ3H0Pj pSEGaTAh+tBYGSvQ4YPYBcV8+qjTxzeNwkw4ARza8EjTwWKP2jWAfA/ay4VobRfqNQ2zLoo84qDtN Uxe0zPE2wobIXELWkbuW/6hoQFPpMlJWz+mbvVms57NAA1HO8F5c1SLFaJ6dN0AQbxrHi45/cQXla 9hSEOJjxcEnJG/ZmcomYHFneM9K1p1K6HcGajiY2BFWkVet9vuHygkLWXVYZ0lr1paLFR52S7T+cf 6dkxOqu1ZiRegvFoyzBUzlLh/elgp3tWUfG2VmJD3lGpB3m5ZhwQ3rFpK8A7cKzgKjwPp61Me0o9z HX53THoG+QG+o0nnIKK7M8+coToTSyznYoq9C3eKeM/J97x9+h9tbizaeUQvWzQOgG8myUJ5u5Dr4 6tv9KXrOJy0iy/dcyreMYV5lwODaFfOeA4Lbnn5vRn9OjuMg1PFhCi3yMI4lA4umXFw0V2/OI5rgW BQELhfvW6mxkihkl6KLZX8m1zcHitCpWaWFjaGVzbGF2IER1YmV5a28gPFNsYXZhLkR1YmV5a29Aa WJtLmNvbT6JAlQEEwEKAD4WIQRVwwtrZ87KC0La2wQ5XNnC34RAdQUCaBpd7AIbAQUJA8JnAAULCQ gHAgYVCgkICwIEFgIDAQIeAQIXgAAKCRA5XNnC34RAdYjFEACiWBEybMt1xjRbEgaZ3UP5i2bSway DwYDvgWW5EbRP7JcqOcZ2vkJwrK3gsqC3FKpjOPh7ecE0I4vrabH1Qobe2N8B2Y396z24mGnkTBbb 16Uz3PC93nFN1BA0wuOjlr1/oOTy5gBY563vybhnXPfSEUcXRd28jI7z8tRyzXh2tL8ZLdv1u4vQ8 E0O7lVJ55p9yGxbwgb5vXU4T2irqRKLxRvU80rZIXoEM7zLf5r7RaRxgwjTKdu6rYMUOfoyEQQZTD 4Xg9YE/X8pZzcbYFs4IlscyK6cXU0pjwr2ssjearOLLDJ7ygvfOiOuCZL+6zHRunLwq2JH/RmwuLV mWWSbgosZD6c5+wu6DxV15y7zZaR3NFPOR5ErpCFUorKzBO1nA4dwOAbNym9OGkhRgLAyxwpea0V0 ZlStfp0kfVaSZYo7PXd8Bbtyjali0niBjPpEVZdgtVUpBlPr97jBYZ+L5GF3hd6WJFbEYgj+5Af7C UjbX9DHweGQ/tdXWRnJHRzorxzjOS3003ddRnPtQDDN3Z/XzdAZwQAs0RqqXrTeeJrLppFUbAP+HZ TyOLVJcAAlVQROoq8PbM3ZKIaOygjj6Yw0emJi1D9OsN2UKjoe4W185vamFWX4Ba41jmCPrYJWAWH fAMjjkInIPg7RLGs8FiwxfcpkILP0YbVWHiNAabQoVmlhY2hlc2xhdiBEdWJleWtvIDx2ZHViZXlr b0BrZXJuZWwub3JnPokCVAQTAQoAPhYhBFXDC2tnzsoLQtrbBDlc2cLfhEB1BQJoVemuAhsBBQkDw mcABQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEDlc2cLfhEB1GRwP/1scX5HO9Sk7dRicLD/fxo ipwEs+UbeA0/TM8OQfdRI4C/tFBYbQCR7lD05dfq8VsYLEyrgeLqP/iRhabLky8LTaEdwoAqPDc/O 9HRffx/faJZqkKc1dZryjqS6b8NExhKOVWmDqN357+Cl/H4hT9wnvjCj1YEqXIxSd/2Pc8+yw/KRC AP7jtRzXHcc/49Lpz/NU5irScusxy2GLKa5o/13jFK3F1fWX1wsOJF8NlTx3rLtBy4GWHITwkBmu8 zI4qcJGp7eudI0l4xmIKKQWanEhVdzBm5UnfyLIa7gQ2T48UbxJlWnMhLxMPrxgtC4Kos1G3zovEy Ep+fJN7D1pwN9aR36jVKvRsX7V4leIDWGzCdfw1FGWkMUfrRwgIl6i3wgqcCP6r9YSWVQYXdmwdMu 1RFLC44iF9340S0hw9+30yGP8TWwd1mm8V/+zsdDAFAoAwisi5QLLkQnEsJSgLzJ9daAsE8KjMthv hUWHdpiUSjyCpigT+KPl9YunZhyrC1jZXERCDPCQVYgaPt+Xbhdjcem/ykv8UVIDAGVXjuk4OW8la nf8SP+uxkTTDKcPHOa5rYRaeNj7T/NClRSd4z6aV3F6pKEJnEGvv/DFMXtSHlbylhyiGKN2Amd0b4 9jg+DW85oNN7q2UYzYuPwkHsFFq5iyF1QggiwYYTpoVXsw Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (by Flathub.org) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-08-14 at 10:31 +0800, Tao Yu wrote: > The btree header node is permanently reserved as node 0. If the on- > disk > bitmap ever presents node 0 as free, the filesystem is already > corrupted and the allocator must not try to instantiate it again. >=20 > Both HFS and HFS+ currently keep scanning the bitmap, set the bit, > and > hand node 0 to hfs_bnode_create()/hfsplus_bnode_create(). HFS+ then > hits the "new node 0 already hashed?" warning reported by syzbot, > while > HFS risks continuing after the same corruption pattern. >=20 > Teach both allocators to treat attempts to allocate node 0 as btree > map > corruption. Force the filesystem read-only, emit the existing repair > hint, and abort the allocation before the code reaches the hashed- > node > warning. >=20 > Reported-by: syzbot+2bf21610eea63cb2ce93@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=3D2bf21610eea63cb2ce93 > Signed-off-by: Tao Yu > --- > =C2=A0fs/hfs/btree.c=C2=A0=C2=A0=C2=A0=C2=A0 | 11 +++++++++++ > =C2=A0fs/hfsplus/btree.c | 11 +++++++++++ > =C2=A02 files changed, 22 insertions(+) >=20 > diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c > index 14114318ec724..9b0b7418ddbd5 100644 > --- a/fs/hfs/btree.c > +++ b/fs/hfs/btree.c > @@ -376,6 +376,17 @@ struct hfs_bnode *hfs_bmap_alloc(struct > hfs_btree *tree) > =C2=A0 if (byte !=3D 0xff) { > =C2=A0 for (m =3D 0x80, i =3D 0; i < 8; m >>=3D > 1, i++) { > =C2=A0 if (!(byte & m)) { > + if (unlikely(!(idx + > i))) { > + pr_warn("(%s > ): %s (cnid 0x%x) map record invalid or bitmap corruption detected, > forcing read-only.\n", > + tree > ->sb->s_id, > + hfs_ > btree_name(tree->cnid), > + tree > ->cnid); > + pr_warn("Run > fsck.hfs to repair.\n"); > + tree->sb- > >s_flags |=3D SB_RDONLY; > + kunmap_local > (data); > + hfs_bnode_pu > t(node); > + return > ERR_PTR(-EIO); > + } > =C2=A0 idx +=3D i; > =C2=A0 data[off] |=3D m; > =C2=A0 set_page_dirty(*page > p); > diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c > index 394542a47e600..3ee92248b2409 100644 > --- a/fs/hfsplus/btree.c > +++ b/fs/hfsplus/btree.c > @@ -561,6 +561,17 @@ struct hfs_bnode *hfs_bmap_alloc(struct > hfs_btree *tree) > =C2=A0 if (byte !=3D 0xff) { > =C2=A0 for (m =3D 0x80, i =3D 0; i < 8; m >>=3D > 1, i++) { > =C2=A0 if (!(byte & m)) { > + if (unlikely(!(idx + > i))) { > + pr_warn("(%s > ): %s (cnid 0x%x) map record invalid or bitmap corruption detected, > forcing read-only.\n", > + tree > ->sb->s_id, > + hfs_ > btree_name(tree->cnid), > + tree > ->cnid); > + pr_warn("Run > fsck.hfsplus to repair.\n"); > + tree->sb- > >s_flags |=3D SB_RDONLY; > + kunmap_local > (data); > + hfs_bnode_pu > t(node); > + return > ERR_PTR(-EIO); > + } > =C2=A0 idx +=3D i; > =C2=A0 data[ctx.off] |=3D m; > =C2=A0 set_page_dirty(page) > ; We already have check [1] in hfs_btree_open(): if (!hfs_bmap_test_bit(node, 0)) { pr_warn("(%s): %s (cnid 0x%x) map record invalid or bitmap corruption detected, forcing read-only.\n", sb->s_id, hfs_btree_name(id), id); pr_warn("Run fsck.hfsplus to repair.\n"); sb->s_flags |=3D SB_RDONLY; } The likewise check has been implemented by patch [2] for HFS. Thanks, Slava. [1] https://elixir.bootlin.com/linux/v7.2-rc6/source/fs/hfsplus/btree.c#L388 [2] https://lore.kernel.org/r/20260716074150.1660-1-aditya.ansh182@gmail.com