floppy: bail out in open() if drive is not responding to block0 read

In case reading of block 0 during open() fails, it is not the right thing
to let open() succeed.

Fix this by introducing FD_OPEN_SHOULD_FAIL_BIT flag, and setting it in
case the bio callback encounters an error while trying to read block 0.

As a bonus, this works around certain broken userspace (blkid), which is
not able to properly handle read()s returning IO errors. Hence be nice to
those, and bail out during open() already; if block 0 is not readable,
read()s are not going to provide any meaningful data anyway.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>

2 files changed, 29 insertions, 10 deletions

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 6b29c4422828..2023043ce7c0 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3691,9 +3691,12 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
         if (!(mode & FMODE_NDELAY)) {
                 if (mode & (FMODE_READ|FMODE_WRITE)) {
                         UDRS->last_checked = 0;
+                        clear_bit(FD_OPEN_SHOULD_FAIL_BIT, &UDRS->flags);
                         check_disk_change(bdev);
                         if (test_bit(FD_DISK_CHANGED_BIT, &UDRS->flags))
                                 goto out;
+                        if (test_bit(FD_OPEN_SHOULD_FAIL_BIT, &UDRS->flags))
+                                goto out;
                 }
                 res = -EROFS;
                 if ((mode & FMODE_WRITE) &&
@@ -3746,17 +3749,29 @@ static unsigned int floppy_check_events(struct gendisk *disk,
  * a disk in the drive, and whether that disk is writable.
  */
 
-static void floppy_rb0_complete(struct bio *bio, int err)
+struct rb0_cbdata {
+        int drive;
+        struct completion complete;
+};
+
+static void floppy_rb0_cb(struct bio *bio, int err)
 {
-        complete((struct completion *)bio->bi_private);
+        struct rb0_cbdata *cbdata = (struct rb0_cbdata *)bio->bi_private;
+        int drive = cbdata->drive;
+
+        if (err) {
+                pr_info("floppy: error %d while reading block 0", err);
+                set_bit(FD_OPEN_SHOULD_FAIL_BIT, &UDRS->flags);
+        }
+        complete(&cbdata->complete);
 }
 
-static int __floppy_read_block_0(struct block_device *bdev)
+static int __floppy_read_block_0(struct block_device *bdev, int drive)
 {
         struct bio bio;
         struct bio_vec bio_vec;
-        struct completion complete;
         struct page *page;
+        struct rb0_cbdata cbdata;
         size_t size;
 
         page = alloc_page(GFP_NOIO);
@@ -3769,6 +3784,8 @@ static int __floppy_read_block_0(struct block_device *bdev)
         if (!size)
                 size = 1024;
 
+        cbdata.drive = drive;
+
         bio_init(&bio);
         bio.bi_io_vec = &bio_vec;
         bio_vec.bv_page = page;
@@ -3779,13 +3796,14 @@ static int __floppy_read_block_0(struct block_device *bdev)
         bio.bi_bdev = bdev;
         bio.bi_iter.bi_sector = 0;
         bio.bi_flags = (1 << BIO_QUIET);
-        init_completion(&complete);
-        bio.bi_private = &complete;
-        bio.bi_end_io = floppy_rb0_complete;
+        bio.bi_private = &cbdata;
+        bio.bi_end_io = floppy_rb0_cb;
 
         submit_bio(READ, &bio);
         process_fd_request();
-        wait_for_completion(&complete);
+
+        init_completion(&cbdata.complete);
+        wait_for_completion(&cbdata.complete);
 
         __free_page(page);
 
@@ -3827,7 +3845,7 @@ static int floppy_revalidate(struct gendisk *disk)
                         UDRS->generation++;
                 if (drive_no_geom(drive)) {
                         /* auto-sensing */
-                        res = __floppy_read_block_0(opened_bdev[drive]);
+                        res = __floppy_read_block_0(opened_bdev[drive], drive);
                 } else {
                         if (cf)
                                 poll_drive(false, FD_RAW_NEED_DISK);
diff --git a/include/uapi/linux/fd.h b/include/uapi/linux/fd.h
index f1f3dd5981b2..84c517cbce90 100644
--- a/include/uapi/linux/fd.h
+++ b/include/uapi/linux/fd.h
@@ -185,7 +185,8 @@ enum {
                                  * to clear media change status */
         FD_UNUSED_BIT,
         FD_DISK_CHANGED_BIT,    /* disk has been changed since last i/o */
-        FD_DISK_WRITABLE_BIT    /* disk is writable */
+        FD_DISK_WRITABLE_BIT,   /* disk is writable */
+        FD_OPEN_SHOULD_FAIL_BIT
 };
 
 #define FDSETDRVPRM _IOW(2, 0x90, struct floppy_drive_params)