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s390/dasd: Fix read for ESE with blksize < 4k

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When reading unformatted tracks on ESE devices, the corresponding memory
areas are simply set to zero for each segment. This is done incorrectly
for blocksizes < 4096.

There are two problems. First, the increment of dst is done using the
counter of the loop (off), which is increased by blksize every
iteration. This leads to a much bigger increment for dst as actually
intended. Second, the increment of dst is done before the memory area
is set to 0, skipping a significant amount of bytes of memory.

This leads to illegal overwriting of memory and ultimately to a kernel
panic.

This is not a problem with 4k blocksize because
blk_queue_max_segment_size is set to PAGE_SIZE, always resulting in a
single iteration for the inner segment loop (bv.bv_len == blksize). The
incorrectly used 'off' value to increment dst is 0 and the correct
memory area is used.

In order to fix this for blksize < 4k, increment dst correctly using the
blksize and only do it at the end of the loop.

Fixes: 5e2b17e712 ("s390/dasd: Add dynamic formatting support for ESE volumes")
Cc: stable@vger.kernel.org # v5.3+
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://lore.kernel.org/r/20220505141733.1989450-4-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jan Höppner 2022-05-05 16:17:31 +02:00 committed by Jens Axboe
parent 71f3871657
commit cd68c48ea1
1 changed files with 3 additions and 4 deletions
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7
drivers/s390/block/dasd_eckd.c
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@ -3285,12 +3285,11 @@ static int dasd_eckd_ese_read(struct dasd_ccw_req *cqr, struct irb *irb)
cqr->proc_bytes = blk_count * blksize;
return 0;
}
if (dst && !skip_block) {
dst += off;
if (dst && !skip_block)
memset(dst, 0, blksize);
} else {
else
skip_block--;
}
dst += blksize;
blk_count++;
}
}