[PATCH] nvmet-tcp: add bounds checks in nvmet_tcp_build_pdu_iovec

[YunJe Shin]

nvmet_tcp_build_pdu_iovec() could walk past cmd->req.sg when a PDU
length or offset exceeds sg_cnt and then use bogus sg->length/offset
values, leading to _copy_to_iter() GPF/KASAN. Guard sg_idx, remaining
entries, and sg->length/offset before building the bvec.

Fixes: 872d26a391da ("nvmet-tcp: add NVMe over TCP target driver")
Signed-off-by: YunJe Shin <ioerts at kookmin.ac.kr>
Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
Reviewed-by: Joonkyo Jung <joonkyoj at yonsei.ac.kr>
---
 drivers/nvme/target/tcp.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c
index 15416ff0eac4..1a62b405d8e6 100644
--- a/drivers/nvme/target/tcp.c
+++ b/drivers/nvme/target/tcp.c
@@ -349,11 +349,14 @@ static void nvmet_tcp_free_cmd_buffers(struct nvmet_tcp_cmd *cmd)
 	cmd->req.sg = NULL;
 }
 
+static void nvmet_tcp_fatal_error(struct nvmet_tcp_queue *queue);
+
 static void nvmet_tcp_build_pdu_iovec(struct nvmet_tcp_cmd *cmd)
 {
 	struct bio_vec *iov = cmd->iov;
 	struct scatterlist *sg;
 	u32 length, offset, sg_offset;
+	unsigned int sg_remaining;
 	int nr_pages;
 
 	length = cmd->pdu_len;
@@ -361,9 +364,22 @@ static void nvmet_tcp_build_pdu_iovec(struct nvmet_tcp_cmd *cmd)
 	offset = cmd->rbytes_done;
 	cmd->sg_idx = offset / PAGE_SIZE;
 	sg_offset = offset % PAGE_SIZE;
+	if (!cmd->req.sg_cnt || cmd->sg_idx >= cmd->req.sg_cnt) {
+		nvmet_tcp_fatal_error(cmd->queue);
+		return;
+	}
 	sg = &cmd->req.sg[cmd->sg_idx];
+	sg_remaining = cmd->req.sg_cnt - cmd->sg_idx;
 
 	while (length) {
+		if (!sg_remaining) {
+			nvmet_tcp_fatal_error(cmd->queue);
+			return;
+		}
+		if (!sg->length || sg->length <= sg_offset) {
+			nvmet_tcp_fatal_error(cmd->queue);
+			return;
+		}
 		u32 iov_len = min_t(u32, length, sg->length - sg_offset);
 
 		bvec_set_page(iov, sg_page(sg), iov_len,
@@ -371,6 +387,7 @@ static void nvmet_tcp_build_pdu_iovec(struct nvmet_tcp_cmd *cmd)
 
 		length -= iov_len;
 		sg = sg_next(sg);
+		sg_remaining--;
 		iov++;
 		sg_offset = 0;
 	}
-- 
2.43.0