[PATCH v2] scsi: target: iscsi: reject invalid size Extended CDB AHS

carlos.bilbao
2026-04-09T02:42:57Z

From: Carlos Bilbao <carlos.bilbao@kernel.org>

If ecdb_ahdr->ahslength is zero, two bugs follow:

kmalloc(be16_to_cpu(ecdb_ahdr->ahslength) + 15, ...)

allocates 15 bytes, but the immediately following memcpy writes
ISCSI_CDB_SIZE (16) bytes into it, a one-byte heap overflow. Also:

memcpy(cdb + ISCSI_CDB_SIZE, ecdb_ahdr->ecdb,
be16_to_cpu(ecdb_ahdr->ahslength) - 1);

(u16)0 - 1 promotes to (int)-1 which converts to SIZE_MAX as size_t,
causing a massive out-of-bounds write.

Reject ahslength == 0 with ISCSI_REASON_PROTOCOL_ERROR before the kmalloc.
Also reject ahslength values that exceed the actual AHS buffer advertised.

Changes in v2:

- Add bounds check: ahslength must not exceed (hdr->hlength * 4) - 3.
- Replace opaque ahslength + 15 with explicit cdb_length variable.

Fixes: 8f1f7d297bce ("scsi: target: iscsi: Add support for extended CDB AHS")
Signed-off-by: Carlos Bilbao (Lambda) <carlos.bilbao@kernel.org>
---
drivers/target/iscsi/iscsi_target.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index e80449f6ce15..1a492965ebdf 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -1100,6 +1100,8 @@ int iscsit_setup_scsi_cmd(struct iscsit_conn *conn, struct iscsit_cmd *cmd,
cdb = hdr->cdb;

if (hdr->hlength) {
+ u16 ahslength;
+
ecdb_ahdr = (struct iscsi_ecdb_ahdr *) (hdr + 1);
if (ecdb_ahdr->ahstype != ISCSI_AHSTYPE_CDB) {
pr_err("Additional Header Segment type %d not supported!\n",
@@ -1108,14 +1110,27 @@ int iscsit_setup_scsi_cmd(struct iscsit_conn *conn, struct iscsit_cmd *cmd,
ISCSI_REASON_CMD_NOT_SUPPORTED, buf);
}

- cdb = kmalloc(be16_to_cpu(ecdb_ahdr->ahslength) + 15,
- GFP_KERNEL);
+ ahslength = be16_to_cpu(ecdb_ahdr->ahslength);
+ if (!ahslength) {
+ pr_err("Extended CDB AHS with zero length, protocol error.\n");
+ return iscsit_add_reject_cmd(cmd,
+ ISCSI_REASON_PROTOCOL_ERROR, buf);
+ }
+ if (ahslength > (hdr->hlength * 4) - 3) {
+ pr_err("Extended CDB AHS length %u exceeds available buffer.\n",
+ ahslength);
+ return iscsit_add_reject_cmd(cmd,
+ ISCSI_REASON_PROTOCOL_ERROR, buf);
+ }
+
+ u16 cdb_length = ahslength - 1 + ISCSI_CDB_SIZE;
+
+ cdb = kmalloc(cdb_length, GFP_KERNEL);
if (cdb == NULL)
return iscsit_add_reject_cmd(cmd,
ISCSI_REASON_BOOKMARK_NO_RESOURCES, buf);
memcpy(cdb, hdr->cdb, ISCSI_CDB_SIZE);
- memcpy(cdb + ISCSI_CDB_SIZE, ecdb_ahdr->ecdb,
- be16_to_cpu(ecdb_ahdr->ahslength) - 1);
+ memcpy(cdb + ISCSI_CDB_SIZE, ecdb_ahdr->ecdb, cdb_length - ISCSI_CDB_SIZE);
}

data_direction = (hdr->flags & ISCSI_FLAG_CMD_WRITE) ? DMA_TO_DEVICE :
--
2.43.0