From: Benjamin Marzinski <bmarz...@redhat.com>
[ Upstream commit 8ca719b81987be690f197e82fdb030580c0a07f3 ]
Due to the semantics of iterate_devices(), the current code allows a
request-based dm table as long as it includes one request-stackable
device. It is supposed to only allow tables where there are no
non-request-stackable devices.
Signed-off-by: Benjamin Marzinski <bmarz...@redhat.com>
Reviewed-by: Mike Snitzer <snit...@kernel.org>
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
LLM Generated explanations, may be completely bogus:
Based on my analysis of the commit and the code context, here's my
assessment:
**Backport Status: YES**
This commit fixes a clear logic bug in the device mapper table
validation code that could lead to incorrect device stacking
configurations. Here's the detailed analysis:
**1. The Bug:**
The original code had inverted logic when checking if devices are
request-stackable:
- The function `device_is_rq_stackable()` returned `true` (non-zero) for
stackable devices
- But `iterate_devices()` stops iteration on non-zero returns and
returns that non-zero value
- The check `!ti->type->iterate_devices(ti, device_is_rq_stackable,
NULL)` would pass if ANY device returned true (stackable), not if ALL
devices were stackable
**2. The Fix:**
- Renamed function to `device_is_not_rq_stackable()` to clarify its
purpose
- Inverted the return values: returns `true` for non-stackable devices
- Changed the logic check to `ti->type->iterate_devices(ti,
device_is_not_rq_stackable, NULL)` without negation
- Now correctly fails if ANY device is not stackable
**3. Why This Should Be Backported:**
a) **Fixes a real bug**: The current code allows invalid device stacking
configurations where request-based DM tables could include non-request-
stackable devices, potentially leading to:
- Data corruption
- System crashes
- I/O failures
b) **Small and contained fix**: The change is minimal (4 lines changed)
and only affects the validation logic without changing any core
functionality
c) **Clear semantics**: The fix makes the code's intent clearer by
renaming the function to match what it actually checks
d) **No architectural changes**: This is purely a bug fix that corrects
validation logic
e) **Critical subsystem**: Device mapper is a critical component used in
production environments for LVM, encryption, and other storage features
f) **Follows stable rules**: This is exactly the type of fix stable
kernels want - important bug fixes with minimal risk
The commit message clearly explains the bug: "the current code allows a
request-based dm table as long as it includes one request-stackable
device. It is supposed to only allow tables where there are no non-
request-stackable devices." This could lead to serious issues in
production systems using device mapper.
drivers/md/dm-table.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 24a857ff6d0b..79ba4bacd0f9 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -899,17 +899,17 @@ static bool dm_table_supports_dax(struct dm_table *t,
return true;
}
-static int device_is_rq_stackable(struct dm_target *ti, struct dm_dev *dev,
- sector_t start, sector_t len, void *data)
+static int device_is_not_rq_stackable(struct dm_target *ti, struct dm_dev *dev,
+ sector_t start, sector_t len, void *data)
{
struct block_device *bdev = dev->bdev;
struct request_queue *q = bdev_get_queue(bdev);
/* request-based cannot stack on partitions! */
if (bdev_is_partition(bdev))
- return false;
+ return true;
- return queue_is_mq(q);
+ return !queue_is_mq(q);
}
static int dm_table_determine_type(struct dm_table *t)
@@ -1005,7 +1005,7 @@ static int dm_table_determine_type(struct dm_table *t)
/* Non-request-stackable devices can't be used for request-based dm */
if (!ti->type->iterate_devices ||
- !ti->type->iterate_devices(ti, device_is_rq_stackable, NULL)) {
+ ti->type->iterate_devices(ti, device_is_not_rq_stackable, NULL)) {
DMERR("table load rejected: including non-request-stackable
devices");
return -EINVAL;
}
--
2.39.5
