[PATCH 4/8] scsi: target: copy a DIF insert tuple across prot sgs

[Jia Jia <physicalmtea@gmail.com>]

sbc_dif_generate() walks each protection sg and stores an 8 byte
t10_pi_tuple while j < sg->length.  The store is not limited to the
bytes that remain in that sg.

vhost-scsi maps a protection buffer with iov_iter_get_pages2() and
keeps each sg inside one page.  Eight PI bytes that start at page
offset 4092 become two sg entries, 4 bytes at offset 4092 and 4 bytes
at offset 0.  The first entry still takes the loop.  For DIF Type 1
the ref_tag store is 4 bytes at paddr + 4, which is the next physical
page.

Software INSERT reaches this function when the fabric does not
advertise DIN_INSERT or DOUT_INSERT.  vhost-scsi advertises only
DIN_PASS and DOUT_PASS.  With fabric_prot_type 1, a READ is
TARGET_PROT_DIN_INSERT and the generated tuple is written into the
guest PI buffer.

Copy the 8 byte tuple across protection sg entries.  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 is left unwritten.  The walk maps each
page with kmap_local_page().

KASAN reports:

  BUG: KASAN: use-after-free in sbc_dif_generate+0x20c/0x640 [target_core_mod]
  Write of size 4

  sbc_dif_generate
  target_complete_ok_work
  process_one_work
  worker_thread
  kthread
  ret_from_fork
  ret_from_fork_asm

Fixes: 66a3d5bc47d2 ("target/sbc: Add sbc_dif_generate software emulation")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/target/target_core_sbc.c | 181 ++++++++++++++++++++++---------
 1 file changed, 132 insertions(+), 49 deletions(-)

diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index adef903652ac..12275ebad95c 100644
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -1250,72 +1250,155 @@ sbc_execute_unmap(struct se_cmd *cmd)
 	return ret;
 }
 
+/*
+ * Copy one 8 byte PI tuple to or from the prot sg.  The data page sits
+ * above the prot map, so a prot sg change drops and restores it.  A
+ * short tail releases both maps and returns false.
+ */
+static bool
+sbc_dif_prot_copy(struct scatterlist **psgp, void **paddrp,
+		  unsigned int *poffp, struct scatterlist **dsgp,
+		  void **daddrp, void *buf, bool to_prot)
+{
+	struct scatterlist *psg = *psgp;
+	struct scatterlist *dsg = *dsgp;
+	void *paddr = *paddrp;
+	void *daddr = *daddrp;
+	unsigned int poff = *poffp;
+	unsigned int len = sizeof(struct t10_pi_tuple);
+	u8 *p = buf;
+
+	while (len) {
+		unsigned int take;
+
+		if (!psg || poff >= psg->length) {
+			if (daddr)
+				kunmap_local(daddr - dsg->offset);
+			if (paddr)
+				kunmap_local(paddr - psg->offset);
+			daddr = NULL;
+			paddr = NULL;
+			psg = psg ? sg_next(psg) : NULL;
+			if (!psg) {
+				*psgp = NULL;
+				*paddrp = NULL;
+				*daddrp = NULL;
+				return false;
+			}
+			poff = 0;
+			if (!psg->length)
+				continue;
+			paddr = kmap_local_page(sg_page(psg)) + psg->offset;
+			daddr = kmap_local_page(sg_page(dsg)) + dsg->offset;
+		}
+
+		take = min_t(unsigned int, len, psg->length - poff);
+		if (to_prot)
+			memcpy(paddr + poff, p, take);
+		else
+			memcpy(p, paddr + poff, take);
+		p += take;
+		poff += take;
+		len -= take;
+	}
+
+	*psgp = psg;
+	*paddrp = paddr;
+	*poffp = poff;
+	*dsgp = dsg;
+	*daddrp = daddr;
+	return true;
+}
+
 void
 sbc_dif_generate(struct se_cmd *cmd)
 {
 	struct se_device *dev = cmd->se_dev;
-	struct t10_pi_tuple *sdt;
-	struct scatterlist *dsg = cmd->t_data_sg, *psg;
+	struct scatterlist *dsg = cmd->t_data_sg;
+	struct scatterlist *psg = cmd->t_prot_sg;
 	sector_t sector = cmd->t_task_lba;
 	void *daddr, *paddr;
-	int i, j, offset = 0;
+	unsigned int poff = 0;
+	int offset = 0;
 	unsigned int block_size = dev->dev_attrib.block_size;
 
-	for_each_sg(cmd->t_prot_sg, psg, cmd->t_prot_nents, i) {
-		paddr = kmap_atomic(sg_page(psg)) + psg->offset;
-		daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
+	if (!psg || !dsg)
+		return;
 
-		for (j = 0; j < psg->length;
-				j += sizeof(*sdt)) {
-			__u16 crc;
-			unsigned int avail;
+	paddr = kmap_local_page(sg_page(psg)) + psg->offset;
+	daddr = kmap_local_page(sg_page(dsg)) + dsg->offset;
 
-			if (offset >= dsg->length) {
-				offset -= dsg->length;
-				kunmap_atomic(daddr - dsg->offset);
-				dsg = sg_next(dsg);
-				if (!dsg) {
-					kunmap_atomic(paddr - psg->offset);
-					return;
-				}
-				daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
-			}
+	for (;;) {
+		struct t10_pi_tuple sdt;
+		struct scatterlist *mark_psg;
+		unsigned int mark_off;
+		__u16 crc;
+		unsigned int avail;
 
-			sdt = paddr + j;
-			avail = min(block_size, dsg->length - offset);
-			crc = crc_t10dif(daddr + offset, avail);
-			if (avail < block_size) {
-				kunmap_atomic(daddr - dsg->offset);
-				dsg = sg_next(dsg);
-				if (!dsg) {
-					kunmap_atomic(paddr - psg->offset);
-					return;
-				}
-				daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
-				offset = block_size - avail;
-				crc = crc_t10dif_update(crc, daddr, offset);
-			} else {
-				offset += block_size;
-			}
+		if (poff >= psg->length && !sg_next(psg))
+			break;
 
-			sdt->guard_tag = cpu_to_be16(crc);
-			if (cmd->prot_type == TARGET_DIF_TYPE1_PROT)
-				sdt->ref_tag = cpu_to_be32(sector & 0xffffffff);
-			sdt->app_tag = 0;
+		mark_psg = psg;
+		mark_off = poff;
+		if (!sbc_dif_prot_copy(&psg, &paddr, &poff, &dsg, &daddr,
+				       &sdt, false))
+			return;
+
+		if (offset >= dsg->length) {
+			offset -= dsg->length;
+			kunmap_local(daddr - dsg->offset);
+			dsg = sg_next(dsg);
+			if (!dsg) {
+				kunmap_local(paddr - psg->offset);
+				return;
+			}
+			daddr = kmap_local_page(sg_page(dsg)) + dsg->offset;
+		}
 
-			pr_debug("DIF %s INSERT sector: %llu guard_tag: 0x%04x"
-				 " app_tag: 0x%04x ref_tag: %u\n",
-				 (cmd->data_direction == DMA_TO_DEVICE) ?
-				 "WRITE" : "READ", (unsigned long long)sector,
-				 sdt->guard_tag, sdt->app_tag,
-				 be32_to_cpu(sdt->ref_tag));
+		avail = min(block_size, dsg->length - offset);
+		crc = crc_t10dif(daddr + offset, avail);
+		if (avail < block_size) {
+			kunmap_local(daddr - dsg->offset);
+			dsg = sg_next(dsg);
+			if (!dsg) {
+				kunmap_local(paddr - psg->offset);
+				return;
+			}
+			daddr = kmap_local_page(sg_page(dsg)) + dsg->offset;
+			offset = block_size - avail;
+			crc = crc_t10dif_update(crc, daddr, offset);
+		} else {
+			offset += block_size;
+		}
 
-			sector++;
+		sdt.guard_tag = cpu_to_be16(crc);
+		if (cmd->prot_type == TARGET_DIF_TYPE1_PROT)
+			sdt.ref_tag = cpu_to_be32(sector & 0xffffffff);
+		sdt.app_tag = 0;
+
+		pr_debug("DIF %s INSERT sector: %llu guard_tag: 0x%04x app_tag: 0x%04x ref_tag: %u\n",
+			 (cmd->data_direction == DMA_TO_DEVICE) ?
+			 "WRITE" : "READ", (unsigned long long)sector,
+			 sdt.guard_tag, sdt.app_tag,
+			 be32_to_cpu(sdt.ref_tag));
+
+		if (psg != mark_psg) {
+			kunmap_local(daddr - dsg->offset);
+			kunmap_local(paddr - psg->offset);
+			psg = mark_psg;
+			paddr = kmap_local_page(sg_page(psg)) + psg->offset;
+			daddr = kmap_local_page(sg_page(dsg)) + dsg->offset;
 		}
+		poff = mark_off;
+		if (!sbc_dif_prot_copy(&psg, &paddr, &poff, &dsg, &daddr,
+				       &sdt, true))
+			return;
 
-		kunmap_atomic(daddr - dsg->offset);
-		kunmap_atomic(paddr - psg->offset);
+		sector++;
 	}
+
+	kunmap_local(daddr - dsg->offset);
+	kunmap_local(paddr - psg->offset);
 }
 
 static sense_reason_t
-- 
2.34.1