Messages in this thread |  | | Date | Tue, 7 Apr 2026 12:23:57 +0300 | | From | Dmitry Bogdanov <> | | Subject | Re: [PATCH] scsi: target: iscsi: reject zero-length Extended CDB AHS |
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On Fri, Apr 03, 2026 at 06:44:29PM -0700, carlos.bilbao@kernel.org wrote: > 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. > > 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 | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c > index e80449f6ce15..8db24d35c762 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 +1110,19 @@ 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); > + } > +
For a complete solution please add a check that AHS fits in the buffer. ahslength must be less or equal than ((hdr->hlength * 4) - 3).
> + cdb = kmalloc(ahslength + 15, GFP_KERNEL);
It took some time to recall what did 15 mean. May be make it clear for everyone too?
u16 cdb_length = ahslength - 1 + ISCSI_CDB_SIZE; cdb = kmalloc(cdb_length, GFP_KERNEL); memcpy(cdb, hdr->cdb, ISCSI_CDB_SIZE); memcpy(cdb + ISCSI_CDB_SIZE, ecdb_ahdr->ecdb, cdb_length - ISCSI_CDB_SIZE);
> 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, ahslength - 1); > } > > data_direction = (hdr->flags & ISCSI_FLAG_CMD_WRITE) ? DMA_TO_DEVICE : > -- > 2.43.0 >
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