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A crafted image can set drVBMSt so that the bitmap byte range resolves to the same buffer_head as the MDB. When writeback later calls lock_buffer() for that bitmap block, the task tries to lock mdb_bh again and self-deadlocks in __lock_buffer(). Reject the image during mount if the bitmap byte range maps to mdb_bh. This checks the aliasing condition that can deadlock writeback without trying to validate unrelated HFS layout fields. Reported-by: Yue Sun Closes: https://lore.kernel.org/all/CAEkJfYMB47v1yOWHB8q2dc8kf=3Duj-rLO=3D+= yMyudwPguJ8Kd3jA@mail.gmail.com/ Signed-off-by: Yue Sun --- fs/hfs/mdb.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/fs/hfs/mdb.c b/fs/hfs/mdb.c index a97cea35ca2e..abaa636db938 100644 --- a/fs/hfs/mdb.c +++ b/fs/hfs/mdb.c @@ -99,8 +99,10 @@ int hfs_mdb_get(struct super_block *sb) char *ptr; int off2, len, size, sect; sector_t part_start, part_size; - loff_t off; + sector_t mdb_block, vbm_first, vbm_last; + loff_t off, vbm_off; __be16 attrib; + u32 bitmap_size; =20 /* set the device driver to 512-byte blocks */ size =3D sb_min_blocksize(sb, HFS_SECTOR_SIZE); @@ -185,6 +187,25 @@ int hfs_mdb_get(struct super_block *sb) sb->s_flags |=3D SB_RDONLY; } =20 + /* + * hfs_mdb_commit() writes the bitmap while holding mdb_bh. Reject + * images whose bitmap range can resolve to the MDB buffer_head. + */ + bitmap_size =3D DIV_ROUND_UP(HFS_SB(sb)->fs_ablocks, BITS_PER_BYTE); + if (!bitmap_size) { + pr_err("bad volume bitmap size\n"); + return -EIO; + } + vbm_off =3D (loff_t)(part_start + be16_to_cpu(mdb->drVBMSt)) << + HFS_SECTOR_SIZE_BITS; + vbm_first =3D vbm_off >> sb->s_blocksize_bits; + vbm_last =3D (vbm_off + bitmap_size - 1) >> sb->s_blocksize_bits; + mdb_block =3D HFS_SB(sb)->mdb_bh->b_blocknr; + if (vbm_first <=3D mdb_block && mdb_block <=3D vbm_last) { + pr_err("volume bitmap overlaps MDB\n"); + return -EIO; + } + /* TRY to get the alternate (backup) MDB. */ sect =3D part_start + part_size - 2; bh =3D sb_bread512(sb, sect, mdb2); --=20 2.34.1