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Petersen" Cc: Jan Engelhardt , Hannes Reinecke , Paolo Bonzini , Akinobu Mita , James Bottomley , linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, linux-kernel@vger.kernel.org, Jia Jia Subject: [PATCH 8/8] scsi: target: skip an escaped DIF block inside the data sg Date: Tue, 6 Oct 2026 17:33:38 +0800 Message-Id: <20261006093338.27342-9-physicalmtea@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20261006093338.27342-1-physicalmtea@gmail.com> References: <20261006093338.27342-1-physicalmtea@gmail.com> Precedence: bulk X-Mailing-List: target-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit sbc_dif_verify() treats an application tag of 0xffff as one skipped logical block and adds block_size to the data cursor. The next tuple folds that cursor across a single sg entry. When the block spans more entries, dsg_off remains past dsg->length and the following CRC reads a full block from that offset. A 512 byte block split 256 + 100 + the remainder, with the 100 byte entry ending on a page and the first tuple escaped, reads the next block from the next physical page. Walk every data sg the skipped block covers. Those data pages are mapped with kmap_local_page(), including the page the cursor moves to. KASAN reports: BUG: KASAN: use-after-free in crc_t10dif_update+0x91/0xf0 Read of size 1 crc_t10dif_update sbc_dif_verify target_execute_cmd vhost_scsi_write_pending transport_generic_new_cmd __target_submit target_queued_submit_work process_one_work worker_thread kthread ret_from_fork ret_from_fork_asm Fixes: 18213afbd8ce ("target: handle odd SG mapping for data transfer memory") Signed-off-by: Jia Jia --- drivers/target/target_core_sbc.c | 46 +++++++++++++++++++++++++++++++- 1 file changed, 45 insertions(+), 1 deletion(-) diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c index 76dbc986e887..7c4f66c2607a 100644 --- a/drivers/target/target_core_sbc.c +++ b/drivers/target/target_core_sbc.c @@ -1521,6 +1521,46 @@ void sbc_dif_copy_prot(struct se_cmd *cmd, unsigned int sectors, bool read, } EXPORT_SYMBOL(sbc_dif_copy_prot); +/* + * Drop @len bytes of the data sg. An escaped PI tuple still covers one + * logical block, which may cross more than one sg entry. + */ +static bool +sbc_dif_consume(struct scatterlist **dsgp, void **daddrp, int *offp, + unsigned int len) +{ + struct scatterlist *dsg = *dsgp; + void *daddr = *daddrp; + int off = *offp; + + while (len) { + unsigned int take; + + if (off >= dsg->length) { + kunmap_local(daddr - dsg->offset); + dsg = sg_next(dsg); + if (!dsg) + return false; + + daddr = kmap_local_page(sg_page(dsg)) + dsg->offset; + off = 0; + if (!dsg->length) { + kunmap_local(daddr - dsg->offset); + return false; + } + } + + take = min_t(unsigned int, len, dsg->length - off); + off += take; + len -= take; + } + + *dsgp = dsg; + *daddrp = daddr; + *offp = off; + return true; +} + sense_reason_t sbc_dif_verify(struct se_cmd *cmd, sector_t start, unsigned int sectors, unsigned int ei_lba, struct scatterlist *psg, int psg_off) @@ -1559,7 +1599,11 @@ sbc_dif_verify(struct se_cmd *cmd, sector_t start, unsigned int sectors, sdt.app_tag, be32_to_cpu(sdt.ref_tag)); if (sdt.app_tag == T10_PI_APP_ESCAPE) { - dsg_off += block_size; + if (!sbc_dif_consume(&dsg, &daddr, &dsg_off, + block_size)) { + kunmap_local(paddr - psg->offset); + return 0; + } goto next; } -- 2.34.1