FAILED: patch "[PATCH] spi: bcm-qspi: reject oversized dummy bytes in mspi exec_mem_op" failed to apply to 5.10-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 9e44f0df3fff215d9033089e85980048c3ac132a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107062402-failed-5.10-9e44f0df3fff@kernel.org' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 9e44f0df3fff215d9033089e85980048c3ac132a Mon Sep 17 00:00:00 2001
From: Weibin Liu <liuwb@xiaopeng.com>
Date: Thu, 15 Oct 2026 10:16:12 +0800
Subject: [PATCH] spi: bcm-qspi: reject oversized dummy bytes in mspi
 exec_mem_op

bcm_qspi_mspi_exec_mem_op() builds a local command buffer cmd[6]
holding one opcode byte, up to four address bytes and one spare
byte, and sets t[0].len = op->addr.nbytes + op->dummy.nbytes + 1.
bcm_qspi_exec_mem_op() only validates op->addr.nbytes <= 4 and never
bounds op->dummy.nbytes, which spi_mem_check_op() also leaves
unrestricted. With addr.nbytes = 4 and dummy.nbytes >= 2 the length
becomes 7 or more, so write_to_hw() reads past cmd[] on the kernel
stack and pushes the leaked bytes into the hardware TXRAM.

Reject operations whose dummy phase does not fit the remaining byte
of cmd[] by requiring op->dummy.nbytes <= 1, so such transfers fall
back to the generic SPI path instead of overrunning the buffer.

Reviewed-by: Guanglei Zhu <zhugl3@xiaopeng.com>
Fixes: 5f195ee7d830c ("spi: bcm-qspi: Implement the spi_mem interface")
Cc: stable@vger.kernel.org # 4.18+
Signed-off-by: Weibin Liu <liuwb@xiaopeng.com>
Link: https://patch.msgid.link/20261015-bcm-qspi-dummy-bytes-v1-1-c319da3c2497@xiaopeng.com
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 drivers/spi/spi-bcm-qspi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-bcm-qspi.c b/drivers/spi/spi-bcm-qspi.c
index 0f96ac59da114..5031b21424795 100644
--- a/drivers/spi/spi-bcm-qspi.c
+++ b/drivers/spi/spi-bcm-qspi.c
@@ -1197,8 +1197,9 @@ static int bcm_qspi_exec_mem_op(struct spi_mem *mem,
 	u32 addr = 0, len;
 	u_char *buf;
 
+	/* cmd[] holds 1 opcode + 4 address + 1 dummy byte at most */
 	if (!op->data.nbytes || !op->addr.nbytes || op->addr.nbytes > 4 ||
-	    op->data.dir != SPI_MEM_DATA_IN)
+	    op->dummy.nbytes > 1 || op->data.dir != SPI_MEM_DATA_IN)
 		return -EOPNOTSUPP;
 
 	buf = op->data.buf.in;
-- 
2.53.0