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0898a81762
The cdrom core never calls set_disk_ro() for a registered device, so
BLKROGET on a CD-ROM device always returns 0 (writable), even when the
drive has no write capabilities and writes will inevitably fail. This
causes problems for userspace that relies on BLKROGET to determine
whether a block device is read-only. For example, systemd's loop device
setup uses BLKROGET to decide whether to create a loop device with
LO_FLAGS_READ_ONLY. Without the read-only flag, writes pass through the
loop device to the CD-ROM and fail with I/O errors. systemd-fsck
similarly checks BLKROGET to decide whether to run fsck in no-repair
mode (-n).
The write-capability bits in cdi->mask come from two different sources:
CDC_DVD_RAM and CDC_CD_RW are populated by the driver from the MODE
SENSE capabilities page (page 0x2A) before register_cdrom() is called,
while CDC_MRW_W and CDC_RAM require the MMC GET CONFIGURATION command
and were only probed by cdrom_open_write() at device open time. This
meant that any attempt to compute the writable state from the full
mask at probe time was incorrect, because the GET CONFIGURATION bits
were still unset (and cdi->mask is initialized such that capabilities
are assumed present).
Fix this by factoring the GET CONFIGURATION probing out of
cdrom_open_write() into a new exported helper,
cdrom_probe_write_features(), and having sr call it from sr_probe()
right after get_capabilities() has populated the MODE SENSE bits.
register_cdrom() then calls set_disk_ro() based on the full
write-capability mask (CDC_DVD_RAM | CDC_MRW_W | CDC_RAM | CDC_CD_RW)
so the block layer reflects the drive's actual write support. The
feature queries used (CDF_MRW and CDF_RWRT via GET CONFIGURATION with
RT=00) report drive-level capabilities that are persistent across
media, so a single probe before register_cdrom() is sufficient and the
redundant probe at open time is dropped.
With set_disk_ro() now accurate, the long-vestigial cd->writeable flag
in sr can go: get_capabilities() used to set cd->writeable based on
the same four mask bits, but because CDC_MRW_W and CDC_RAM default to
"capability present" in cdi->mask and aren't touched by MODE SENSE,
the condition that gated cd->writeable was always true, making it
unconditionally 1. Replace the corresponding gate in sr_init_command()
with get_disk_ro(cd->disk), which turns a previously no-op check into
a real one and also catches kernel-internal bio writers that bypass
blkdev_write_iter()'s bdev_read_only() check.
The sd driver (SCSI disks) does not have this problem because it
checks the MODE SENSE Write Protect bit and calls set_disk_ro()
accordingly. The sr driver cannot use the same approach because the
MMC specification does not define the WP bit in the MODE SENSE
device-specific parameter byte for CD-ROM devices.
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Daan De Meyer <daan@amutable.com>
Reviewed-by: Phillip Potter <phil@philpotter.co.uk>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://patch.msgid.link/20260427210139.1400-2-phil@philpotter.co.uk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
78 lines
2.5 KiB
C
78 lines
2.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* sr.h by David Giller
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* CD-ROM disk driver header file
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*
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* adapted from:
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* sd.h Copyright (C) 1992 Drew Eckhardt
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* SCSI disk driver header file by
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* Drew Eckhardt
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*
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* <drew@colorado.edu>
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*
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* Modified by Eric Youngdale eric@andante.org to
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* add scatter-gather, multiple outstanding request, and other
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* enhancements.
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*/
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#ifndef _SR_H
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#define _SR_H
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#include <linux/mutex.h>
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#define MAX_RETRIES 3
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#define SR_TIMEOUT (30 * HZ)
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struct scsi_device;
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/* The CDROM is fairly slow, so we need a little extra time */
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/* In fact, it is very slow if it has to spin up first */
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#define IOCTL_TIMEOUT 30*HZ
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typedef struct scsi_cd {
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unsigned capacity; /* size in blocks */
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struct scsi_device *device;
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unsigned int vendor; /* vendor code, see sr_vendor.c */
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unsigned long ms_offset; /* for reading multisession-CD's */
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unsigned use:1; /* is this device still supportable */
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unsigned xa_flag:1; /* CD has XA sectors ? */
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unsigned readcd_known:1; /* drive supports READ_CD (0xbe) */
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unsigned readcd_cdda:1; /* reading audio data using READ_CD */
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unsigned media_present:1; /* media is present */
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/* GET_EVENT spurious event handling, blk layer guarantees exclusion */
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int tur_mismatch; /* nr of get_event TUR mismatches */
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bool tur_changed:1; /* changed according to TUR */
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bool get_event_changed:1; /* changed according to GET_EVENT */
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bool ignore_get_event:1; /* GET_EVENT is unreliable, use TUR */
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struct cdrom_device_info cdi;
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struct mutex lock;
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struct gendisk *disk;
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} Scsi_CD;
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#define sr_printk(prefix, cd, fmt, a...) \
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sdev_prefix_printk(prefix, (cd)->device, (cd)->cdi.name, fmt, ##a)
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int sr_do_ioctl(Scsi_CD *, struct packet_command *);
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int sr_lock_door(struct cdrom_device_info *, int);
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int sr_tray_move(struct cdrom_device_info *, int);
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int sr_drive_status(struct cdrom_device_info *, int);
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int sr_disk_status(struct cdrom_device_info *);
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int sr_get_last_session(struct cdrom_device_info *, struct cdrom_multisession *);
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int sr_get_mcn(struct cdrom_device_info *, struct cdrom_mcn *);
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int sr_reset(struct cdrom_device_info *);
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int sr_select_speed(struct cdrom_device_info *cdi, unsigned long speed);
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int sr_audio_ioctl(struct cdrom_device_info *, unsigned int, void *);
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int sr_is_xa(Scsi_CD *);
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/* sr_vendor.c */
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void sr_vendor_init(Scsi_CD *);
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int sr_cd_check(struct cdrom_device_info *);
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int sr_set_blocklength(Scsi_CD *, int blocklength);
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#endif
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