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scsi: libiscsi_tcp: Check the data direction of a Data-In PDU

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The Data-In branch of iscsi_tcp_hdr_dissect() resolves the ITT to a task
and copies the PDU's data segment into that command's scatterlist without
asking whether the command was reading. iscsi_tcp_r2t_rsp() in the same
file does ask, and rejects an R2T for a command that is not DMA_TO_DEVICE.

A target that answers a WRITE command's ITT with a Data-In therefore has
the initiator write target-supplied bytes into the pages that write was
about to send. Those are the caller's own pinned pages for an O_DIRECT
write, and page cache pages for a buffered one.

Observed against a test target that emits one 512-byte Data-In naming a 128
KB write's ITT, after the R2T for that write. With O_DIRECT the caller's
buffer ends up holding 512 bytes of the target's data while pwrite()
returns 131072. Buffered is quieter: pwrite() and fsync() both succeed,
nothing is logged, and reading those blocks back returns the target's bytes
out of the page cache without a command going on the wire.

Check the direction before using the scatterlist, the way the R2T path
already does.

Cc: stable@vger.kernel.org
Signed-off-by: Yehyeong Lee <yhlee@isslab.korea.ac.kr>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Link: https://patch.msgid.link/20260801133635.1986706-1-yhlee@isslab.korea.ac.kr
Fixes: a081c13e39 ("[SCSI] iscsi_tcp: split module into lib and lld")
Signed-off-by: Martin K. Petersen (Oracle) <mkp@kernel.org>
This commit is contained in:
Yehyeong Lee 2026-08-01 22:36:35 +09:00 committed by Martin K. Petersen (Oracle)
parent c9ee651133
commit bce07e2f37
1 changed files with 3 additions and 0 deletions
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3
drivers/scsi/libiscsi_tcp.c
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@ -480,6 +480,9 @@ static int iscsi_tcp_data_in(struct iscsi_conn *conn, struct iscsi_task *task)
int datasn = be32_to_cpu(rhdr->datasn);
unsigned total_in_length = task->sc->sdb.length;
if (task->sc->sc_data_direction != DMA_FROM_DEVICE)
return ISCSI_ERR_PROTO;
/*
* lib iscsi will update this in the completion handling if there
* is status.