Messages in this thread |  | | Date | Wed, 8 Apr 2026 19:23:46 -0700 | | Subject | Re: [PATCH] scsi: target: iscsi: reject zero-length Extended CDB AHS | | From | Carlos Bilbao <> |
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Hello,
On 4/7/26 02:23, Dmitry Bogdanov wrote: > 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).
For sure, I'll send a v2 including that.
> >> + 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); >
Agreed!
>> 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 >>
Thanks,
Carlos
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