5.4-stable review patch. If anyone has any objections, please let me know.
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From: Simon Tatham anakin@pobox.com
[ 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 anakin@pobox.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 6dae4ca09be5f..199b92f6a9941 100644 --- a/fs/affs/file.c +++ b/fs/affs/file.c @@ -724,7 +724,8 @@ 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;