isofs: fix Rock Ridge CE extent validation on multisession media

Commit a36d990f5913 ("isofs: validate Rock Ridge CE continuation extent
against volume size") compares the CE extent directly with s_nzones.  The
extent is an absolute block number, while s_nzones is the number of blocks
relative to the selected ISO session.  The comparison is therefore wrong
when a multisession disc starts at a non-zero block.

isofs_get_last_session() selects the last session on multisession
media, and its volume descriptors describe a volume beginning at that
session's LBA.
For example, a session beginning at LBA 45447 with 64 blocks can contain a
valid CE at absolute LBA 45467.  The existing check rejects that CE, so the
ER continuation record is not read, Rock Ridge is disabled, and the mount
falls back to Joliet names.

Save the selected session start in filesystem-block units and validate the
CE extent against the half-open interval [session_start, session_end).
Scale the session length to the same block units and retain a separate
block-device limit.  The lower bound is intentional: accepting arbitrary
blocks before the selected session could make a CE read data from a
previous session or another filesystem on the device.

Only apply the bounds check when cont_extent is non-zero.  A zero extent is
the in-memory sentinel indicating that no CE continuation was found, rather
than a request to read block zero.

For a single-session image, session_start is zero and the effective volume
boundary remains unchanged.

Build-tested with:

    make CONFIG_RUST= CONFIG_RUST_DRIVERS= fs/isofs/

Fixes: a36d990f5913 ("isofs: validate Rock Ridge CE continuation extent against volume size")
Cc: stable@vger.kernel.org
Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
Link: https://patch.msgid.link/20260907082602.3777551-1-liubaolin12138@163.com
Signed-off-by: Jan Kara <jack@suse.cz>

0 files changed, 0 insertions, 0 deletions