linux-kernel - [PATCH AUTOSEL 4.14 08/30] scsi: target: tcmu: Fix crash on ARM during cmd completion

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Date:   Fri, 21 Aug 2020 12:18:35 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Bodo Stroesser <bstroesser@...fujitsu.com>,
        JiangYu <lnsyyj@...mail.com>,
        Mike Christie <michael.christie@...cle.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Sasha Levin <sashal@...nel.org>, linux-scsi@...r.kernel.org,
        target-devel@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 08/30] scsi: target: tcmu: Fix crash on ARM during cmd completion

From: Bodo Stroesser <bstroesser@...fujitsu.com>

[ Upstream commit 5a0c256d96f020e4771f6fd5524b80f89a2d3132 ]

If tcmu_handle_completions() has to process a padding shorter than
sizeof(struct tcmu_cmd_entry), the current call to
tcmu_flush_dcache_range() with sizeof(struct tcmu_cmd_entry) as length
param is wrong and causes crashes on e.g. ARM, because
tcmu_flush_dcache_range() in this case calls
flush_dcache_page(vmalloc_to_page(start)); with start being an invalid
address above the end of the vmalloc'ed area.

The fix is to use the minimum of remaining ring space and sizeof(struct
tcmu_cmd_entry) as the length param.

The patch was tested on kernel 4.19.118.

See https://bugzilla.kernel.org/show_bug.cgi?id=208045#c10

Link: https://lore.kernel.org/r/20200629093756.8947-1-bstroesser@ts.fujitsu.com
Tested-by: JiangYu <lnsyyj@...mail.com>
Acked-by: Mike Christie <michael.christie@...cle.com>
Signed-off-by: Bodo Stroesser <bstroesser@...fujitsu.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/target/target_core_user.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index c4a5fb6f038fc..96601fda47b18 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -997,7 +997,14 @@ static unsigned int tcmu_handle_completions(struct tcmu_dev *udev)
 		struct tcmu_cmd_entry *entry = (void *) mb + CMDR_OFF + udev->cmdr_last_cleaned;
 		struct tcmu_cmd *cmd;
 
-		tcmu_flush_dcache_range(entry, sizeof(*entry));
+		/*
+		 * Flush max. up to end of cmd ring since current entry might
+		 * be a padding that is shorter than sizeof(*entry)
+		 */
+		size_t ring_left = head_to_end(udev->cmdr_last_cleaned,
+					       udev->cmdr_size);
+		tcmu_flush_dcache_range(entry, ring_left < sizeof(*entry) ?
+					ring_left : sizeof(*entry));
 
 		if (tcmu_hdr_get_op(entry->hdr.len_op) == TCMU_OP_PAD) {
 			UPDATE_HEAD(udev->cmdr_last_cleaned,
-- 
2.25.1