[PATCH 5/8] scsi: target: copy a DIF verify tuple across prot sgs

[Jia Jia <physicalmtea@gmail.com>]

sbc_dif_verify() loads an 8 byte t10_pi_tuple while i < psg->length.
A protection sg shorter than 8 bytes still enters the loop.

vhost-scsi keeps each sg inside one page. Eight PI bytes that start
at page offset 4092 are mapped as 4 bytes at that offset and 4 bytes
on the next guest page. The first sg still satisfies i < length, and
the tuple read continues into the next physical page.

Software verify runs when the fabric does not advertise DOUT_STRIP.
vhost-scsi advertises only DIN_PASS and DOUT_PASS. With
fabric_prot_type 1, a WRITE is TARGET_PROT_DOUT_STRIP and
sbc_dif_verify() reads the guest PI buffer.

Copy the 8 byte tuple across protection sg entries before the check.
Four bytes at the end of one entry and four at the start of the next
stay one tuple.  A tail with no following entry fails the command.

KASAN reports:

  BUG: KASAN: use-after-free in sbc_dif_verify+0x5ab/0x790 [target_core_mod]
  Read of size 4

  sbc_dif_verify
  target_execute_cmd
  vhost_scsi_write_pending
  transport_generic_new_cmd
  __target_submit
  target_queued_submit_work
  process_one_work
  worker_thread
  kthread
  ret_from_fork
  ret_from_fork_asm

Fixes: 18213afbd8ce ("target: handle odd SG mapping for data transfer memory")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/target/target_core_sbc.c | 117 ++++++++++++++++---------------
 1 file changed, 60 insertions(+), 57 deletions(-)

diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index 12275ebad95c..c0aeb8886743 100644
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -1492,81 +1492,84 @@ sbc_dif_verify(struct se_cmd *cmd, sector_t start, unsigned int sectors,
 	       unsigned int ei_lba, struct scatterlist *psg, int psg_off)
 {
 	struct se_device *dev = cmd->se_dev;
-	struct t10_pi_tuple *sdt;
 	struct scatterlist *dsg = cmd->t_data_sg;
 	sector_t sector = start;
 	void *daddr, *paddr;
-	int i;
 	sense_reason_t rc;
+	unsigned int poff = psg_off;
 	int dsg_off = 0;
 	unsigned int block_size = dev->dev_attrib.block_size;
 
-	for (; psg && sector < start + sectors; psg = sg_next(psg)) {
-		paddr = kmap_atomic(sg_page(psg)) + psg->offset;
-		daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
-
-		for (i = psg_off; i < psg->length &&
-				sector < start + sectors;
-				i += sizeof(*sdt)) {
-			__u16 crc;
-			unsigned int avail;
-
-			if (dsg_off >= dsg->length) {
-				dsg_off -= dsg->length;
-				kunmap_atomic(daddr - dsg->offset);
-				dsg = sg_next(dsg);
-				if (!dsg) {
-					kunmap_atomic(paddr - psg->offset);
-					return 0;
-				}
-				daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
-			}
+	if (!psg || !dsg)
+		return 0;
 
-			sdt = paddr + i;
+	paddr = kmap_local_page(sg_page(psg)) + psg->offset;
+	daddr = kmap_local_page(sg_page(dsg)) + dsg->offset;
 
-			pr_debug("DIF READ sector: %llu guard_tag: 0x%04x"
-				 " app_tag: 0x%04x ref_tag: %u\n",
-				 (unsigned long long)sector, sdt->guard_tag,
-				 sdt->app_tag, be32_to_cpu(sdt->ref_tag));
+	while (sector < start + sectors) {
+		struct t10_pi_tuple sdt;
+		__u16 crc;
+		unsigned int avail;
 
-			if (sdt->app_tag == T10_PI_APP_ESCAPE) {
-				dsg_off += block_size;
-				goto next;
-			}
+		if (poff >= psg->length && !sg_next(psg))
+			break;
+
+		if (!sbc_dif_prot_copy(&psg, &paddr, &poff, &dsg, &daddr,
+				       &sdt, false)) {
+			cmd->sense_info = sector;
+			return TCM_LOGICAL_BLOCK_GUARD_CHECK_FAILED;
+		}
 
-			avail = min(block_size, dsg->length - dsg_off);
-			crc = crc_t10dif(daddr + dsg_off, avail);
-			if (avail < block_size) {
-				kunmap_atomic(daddr - dsg->offset);
-				dsg = sg_next(dsg);
-				if (!dsg) {
-					kunmap_atomic(paddr - psg->offset);
-					return 0;
-				}
-				daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
-				dsg_off = block_size - avail;
-				crc = crc_t10dif_update(crc, daddr, dsg_off);
-			} else {
-				dsg_off += block_size;
+		pr_debug("DIF READ sector: %llu guard_tag: 0x%04x app_tag: 0x%04x ref_tag: %u\n",
+			 (unsigned long long)sector, sdt.guard_tag,
+			 sdt.app_tag, be32_to_cpu(sdt.ref_tag));
+
+		if (sdt.app_tag == T10_PI_APP_ESCAPE) {
+			dsg_off += block_size;
+			goto next;
+		}
+
+		if (dsg_off >= dsg->length) {
+			dsg_off -= dsg->length;
+			kunmap_local(daddr - dsg->offset);
+			dsg = sg_next(dsg);
+			if (!dsg) {
+				kunmap_local(paddr - psg->offset);
+				return 0;
 			}
+			daddr = kmap_local_page(sg_page(dsg)) + dsg->offset;
+		}
 
-			rc = sbc_dif_v1_verify(cmd, sdt, crc, sector, ei_lba);
-			if (rc) {
-				kunmap_atomic(daddr - dsg->offset);
-				kunmap_atomic(paddr - psg->offset);
-				cmd->sense_info = sector;
-				return rc;
+		avail = min(block_size, dsg->length - dsg_off);
+		crc = crc_t10dif(daddr + dsg_off, avail);
+		if (avail < block_size) {
+			kunmap_local(daddr - dsg->offset);
+			dsg = sg_next(dsg);
+			if (!dsg) {
+				kunmap_local(paddr - psg->offset);
+				return 0;
 			}
-next:
-			sector++;
-			ei_lba++;
+			daddr = kmap_local_page(sg_page(dsg)) + dsg->offset;
+			dsg_off = block_size - avail;
+			crc = crc_t10dif_update(crc, daddr, dsg_off);
+		} else {
+			dsg_off += block_size;
 		}
 
-		psg_off = 0;
-		kunmap_atomic(daddr - dsg->offset);
-		kunmap_atomic(paddr - psg->offset);
+		rc = sbc_dif_v1_verify(cmd, &sdt, crc, sector, ei_lba);
+		if (rc) {
+			kunmap_local(daddr - dsg->offset);
+			kunmap_local(paddr - psg->offset);
+			cmd->sense_info = sector;
+			return rc;
+		}
+next:
+		sector++;
+		ei_lba++;
 	}
 
+	kunmap_local(daddr - dsg->offset);
+	kunmap_local(paddr - psg->offset);
 	return 0;
 }
 EXPORT_SYMBOL(sbc_dif_verify);
-- 
2.34.1