From 397e6aa03f9abf3018b23fdc39a5a75d5bead854 Mon Sep 17 00:00:00 2001 From: Simon Tatham Date: Thu, 20 Feb 2025 08:14:44 +0000 Subject: [PATCH] affs: don't write overlarge OFS data block size fields [ Upstream commit 011ea742a25a77bac3d995f457886a67d178c6f0 ] If a data sector on an OFS floppy contains a value > 0x1e8 (the largest amount of data that fits in the sector after its header), then an Amiga reading the file can return corrupt data, by taking the overlarge size at its word and reading past the end of the buffer it read the disk sector into! The cause: when affs_write_end_ofs() writes data to an OFS filesystem, the new size field for a data block was computed by adding the amount of data currently being written (into the block) to the existing value of the size field. This is correct if you're extending the file at the end, but if you seek backwards in the file and overwrite _existing_ data, it can lead to the size field being larger than the maximum legal value. This commit changes the calculation so that it sets the size field to the max of its previous size and the position within the block that we just wrote up to. Signed-off-by: Simon Tatham Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/affs/file.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/affs/file.c b/fs/affs/file.c index 88d4e6263df9..2000241431d5 100644 --- a/fs/affs/file.c +++ b/fs/affs/file.c @@ -726,7 +726,8 @@ static int affs_write_end_ofs(struct file *file, struct address_space *mapping, tmp = min(bsize - boff, to - from); BUG_ON(boff + tmp > bsize || tmp > bsize); memcpy(AFFS_DATA(bh) + boff, data + from, tmp); - be32_add_cpu(&AFFS_DATA_HEAD(bh)->size, tmp); + AFFS_DATA_HEAD(bh)->size = cpu_to_be32( + max(boff + tmp, be32_to_cpu(AFFS_DATA_HEAD(bh)->size))); affs_fix_checksum(sb, bh); mark_buffer_dirty_inode(bh, inode); written += tmp;