block: initialize integrity buffer to zero before writing it to media

Metadata added by bio_integrity_prep is using plain kmalloc, which leads
to random kernel memory being written media.  For PI metadata this is
limited to the app tag that isn't used by kernel generated metadata,
but for non-PI metadata the entire buffer leaks kernel memory.

Fix this by adding the __GFP_ZERO flag to allocations for writes.

Fixes: 7ba1ba12 ("block: Block layer data integrity support")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20240613084839.1044015-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/bio-integrity.c

@@ -432,6 +432,7 @@ bool bio_integrity_prep(struct bio *bio)
 	unsigned long start, end;
 	unsigned int len, nr_pages;
 	unsigned int bytes, offset, i;
+	gfp_t gfp = GFP_NOIO;
 
 	if (!bi)
 		return true;
@@ -454,11 +455,19 @@ bool bio_integrity_prep(struct bio *bio)
 		if (!bi->profile->generate_fn ||
 		    !(bi->flags & BLK_INTEGRITY_GENERATE))
 			return true;
+
+		/*
+		 * Zero the memory allocated to not leak uninitialized kernel
+		 * memory to disk.  For PI this only affects the app tag, but
+		 * for non-integrity metadata it affects the entire metadata
+		 * buffer.
+		 */
+		gfp |= __GFP_ZERO;
 	}
 
 	/* Allocate kernel buffer for protection data */
 	len = bio_integrity_bytes(bi, bio_sectors(bio));
-	buf = kmalloc(len, GFP_NOIO);
+	buf = kmalloc(len, gfp);
 	if (unlikely(buf == NULL)) {
 		printk(KERN_ERR "could not allocate integrity buffer\n");
 		goto err_end_io;