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([2600:1700:6476:1430:fbb1:1a9c:e8af:d8ed]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-64e91c29074sm2734401d50.20.2026.03.18.20.01.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 20:01:50 -0700 (PDT) Message-ID: <43be87e694ed6fe291990226624559e7f01820d9.camel@dubeyko.com> Subject: Re: [PATCH v7 2/2] hfsplus: validate b-tree node 0 bitmap at mount time From: Viacheslav Dubeyko To: Shardul Bankar , glaubitz@physik.fu-berlin.de, frank.li@vivo.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: janak@mpiricsoftware.com, janak@mpiric.us, shardulsb08@gmail.com, syzbot+1c8ff72d0cd8a50dfeaa@syzkaller.appspotmail.com Date: Wed, 18 Mar 2026 20:01:48 -0700 In-Reply-To: <20260318073823.3933718-3-shardul.b@mpiricsoftware.com> References: <20260318073823.3933718-1-shardul.b@mpiricsoftware.com> <20260318073823.3933718-3-shardul.b@mpiricsoftware.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 3.58.3 (by Flathub.org) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-03-18 at 13:08 +0530, Shardul Bankar wrote: > Syzkaller reported an issue with corrupted HFS+ images where the b- > tree > allocation bitmap indicates that the header node (Node 0) is free. > Node 0 > must always be allocated as it contains the b-tree header record and > the > allocation bitmap itself. Violating this invariant leads to allocator > corruption, which cascades into kernel panics or undefined behavior > when > the filesystem attempts to allocate blocks. >=20 > Prevent trusting a corrupted allocator state by adding a validation > check > during hfs_btree_open(). Introduce the hfs_bmap_test_bit() helper > (utilizing the newly added map-access API) to safely verify that the > MSB > of the first bitmap byte (representing Node 0) is marked as > allocated. > The helper returns a boolean, allowing the caller to safely catch > both > structural IO errors and illegally cleared bits in a single check. >=20 > If corruption is detected, print a warning identifying the specific > corrupted tree and force the filesystem to mount read-only > (SB_RDONLY). > This prevents kernel panics from corrupted images while enabling data > recovery. >=20 > As a minor cleanup to support the warning logs, replace the verbose > CNID > logic with cleaner macro definitions (using official structural names > like > "Extents Overflow File") and a dedicated string lookup helper. >=20 > Reported-by: syzbot+1c8ff72d0cd8a50dfeaa@syzkaller.appspotmail.com > Link: https://syzkaller.appspot.com/bug?extid=3D1c8ff72d0cd8a50dfeaa > Link: > https://lore.kernel.org/all/20260315172005.2066677-1-shardul.b@mpiricsoft= ware.com/ > Signed-off-by: Shardul Bankar > --- > =C2=A0fs/hfsplus/btree.c | 60 > ++++++++++++++++++++++++++++++++++++++++++++++ > =C2=A01 file changed, 60 insertions(+) >=20 > diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c > index 64d168347b4b..04304f952f6b 100644 > --- a/fs/hfsplus/btree.c > +++ b/fs/hfsplus/btree.c > @@ -185,6 +185,32 @@ static struct page *hfs_bmap_get_map_page(struct > hfs_bnode *node, struct hfs_bma > =C2=A0 return node->page[ctx->page_idx]; > =C2=A0} > =C2=A0 > +/** > + * hfs_bmap_test_bit - test a bit in the b-tree map > + * @node: the b-tree node containing the map record > + * @node_bit_idx: the relative bit index within the node's map > record > + * > + * Returns true if set, false if clear or on failure. > + */ > +static bool hfs_bmap_test_bit(struct hfs_bnode *node, u32 > node_bit_idx) > +{ > + struct hfs_bmap_ctx ctx; > + struct page *page; > + u8 *bmap, byte, mask; > + > + page =3D hfs_bmap_get_map_page(node, &ctx, node_bit_idx / > BITS_PER_BYTE); > + if (IS_ERR(page)) > + return false; > + > + bmap =3D kmap_local_page(page); > + byte =3D bmap[ctx.off]; > + kunmap_local(bmap); > + > + mask =3D 1 << (7 - (node_bit_idx % BITS_PER_BYTE)); > + return (byte & mask) !=3D 0; > +} > + > + > =C2=A0/** > =C2=A0 * hfs_bmap_clear_bit - clear a bit in the b-tree map > =C2=A0 * @node: the b-tree node containing the map record > @@ -218,12 +244,32 @@ static int hfs_bmap_clear_bit(struct hfs_bnode > *node, u32 node_bit_idx) > =C2=A0 return 0; > =C2=A0} > =C2=A0 > +#define HFS_EXTENT_TREE_NAME=C2=A0 "Extents Overflow File" > +#define HFS_CATALOG_TREE_NAME "Catalog File" > +#define HFS_ATTR_TREE_NAME=C2=A0=C2=A0=C2=A0 "Attributes File" > +#define HFS_UNKNOWN_TREE_NAME "Unknown B-tree" > + > +static const char *hfs_btree_name(u32 cnid) > +{ > + switch (cnid) { > + case HFSPLUS_EXT_CNID: > + return HFS_EXTENT_TREE_NAME; > + case HFSPLUS_CAT_CNID: > + return HFS_CATALOG_TREE_NAME; > + case HFSPLUS_ATTR_CNID: > + return HFS_ATTR_TREE_NAME; > + default: > + return HFS_UNKNOWN_TREE_NAME; > + } > +} > + > =C2=A0/* Get a reference to a B*Tree and do some initial checks */ > =C2=A0struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id) > =C2=A0{ > =C2=A0 struct hfs_btree *tree; > =C2=A0 struct hfs_btree_header_rec *head; > =C2=A0 struct address_space *mapping; > + struct hfs_bnode *node; > =C2=A0 struct inode *inode; > =C2=A0 struct page *page; > =C2=A0 unsigned int size; > @@ -331,6 +377,20 @@ struct hfs_btree *hfs_btree_open(struct > super_block *sb, u32 id) > =C2=A0 > =C2=A0 kunmap_local(head); > =C2=A0 put_page(page); > + > + node =3D hfs_bnode_find(tree, HFSPLUS_TREE_HEAD); > + if (IS_ERR(node)) > + goto free_inode; > + > + 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; > + } > + > + hfs_bnode_put(node); > + > =C2=A0 return tree; > =C2=A0 > =C2=A0 fail_page: Looks good. Reviewed-by: Viacheslav Dubeyko The xfstests run hasn't revealed any new issues. Tested-by: Viacheslav Dubeyko Thanks, Slava.