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[PATCH v3] scsi: scsi_debug: fix REPORT ZONES alloc_len underflow OOB write

Ibrahim Hashimov posted 1 patch 2 weeks, 1 day ago
There is a newer version of this series
drivers/scsi/scsi_debug.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
[PATCH v3] scsi: scsi_debug: fix REPORT ZONES alloc_len underflow OOB write
Posted by Ibrahim Hashimov 2 weeks, 1 day ago 
resp_report_zones() derives the number of zone descriptors that fit in
the reply buffer from the command allocation length:

	rep_max_zones = (alloc_len - 64) >> ilog2(RZONES_DESC_HD);

	arr = kzalloc(alloc_len, GFP_ATOMIC | __GFP_NOWARN);

alloc_len is taken directly from the CDB and is fully controlled by the
initiator. When alloc_len is smaller than the 64-byte report header
(RZONES_DESC_HD), the subtraction underflows and rep_max_zones becomes a
huge value. The buffer is then allocated with only alloc_len bytes, which
is smaller than the 64-byte header the code unconditionally writes, and
the descriptor loop is bounded by the bogus rep_max_zones. Both the header
store and the following zone descriptors are then written past the end of
the undersized allocation, corrupting adjacent slab memory.

Fix it by sizing the buffer to a whole number of 64-byte blocks that
cover the requested allocation length:

	rep_max_zones =
		(ALIGN((u64)alloc_len, RZONES_DESC_HD) - RZONES_DESC_HD)
		>> ilog2(RZONES_DESC_HD);
	arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1);

	arr = kzalloc(arr_len, GFP_ATOMIC | __GFP_NOWARN);

RZONES_DESC_HD is a power of two, so ALIGN() rounds alloc_len up to the
next multiple of 64 and rep_max_zones can no longer underflow: for any
alloc_len of 1 to 64 it is 0, so only the header is built. arr_len is
always RZONES_DESC_HD * (rep_max_zones + 1), which is exactly large enough
for the header plus every descriptor the loop may write, so the report is
always assembled within bounds, including a possibly partial trailing
zone descriptor. The existing copy-out still transfers only what the host
asked for:

	fill_from_dev_buffer(scp, arr, min_t(u32, alloc_len, rep_len));

so an allocation length that ends in the middle of a zone descriptor
returns the correctly truncated partial descriptor, as permitted by the
SCSI/ZBC specifications, while never reading past arr_len.

The aligned length and the buffer size are computed in 64-bit (alloc_len
is cast to u64 before ALIGN and the size product uses a u64 block size) so
a crafted allocation length near U32_MAX cannot wrap them to a small value;
such a request simply fails the large allocation and returns a check
condition instead of overflowing the buffer.

This was found by static analysis. A KASAN slab-out-of-bounds runtime
reproduction of the original underflow is being re-run against the ALIGN
based fix and will be reported separately.

Fixes: 7db0e0c8190a ("scsi: scsi_debug: Fix buffer size of REPORT ZONES command")
Suggested-by: Damien Le Moal <dlemoal@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
Assisted-by: AuditCode-AI:2026.07
---
v3: adopt Damien Le Moal's ALIGN-based buffer sizing (Suggested-by) so a
partial trailing zone descriptor is filled and returned per the SCSI/ZBC
specs; v2 emitted only the report header for allocation lengths of 65..127
bytes. The buffer is sized to a whole number of 64-byte blocks covering
alloc_len; the existing min(alloc_len, rep_len) copy-out still truncates the
transfer to the requested length.
Computed in 64-bit to avoid a u32 wrap of the aligned length/size for
allocation lengths near U32_MAX (which would otherwise reintroduce the
overflow).
v2: https://lore.kernel.org/linux-scsi/20260709194824.50777-1-security@auditcode.ai/
 drivers/scsi/scsi_debug.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 9d1c9c41d0f9..12e5a8624511 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -5890,6 +5890,7 @@ static int resp_report_zones(struct scsi_cmnd *scp,
 	u32 alloc_len, rep_opts, rep_len;
 	bool partial;
 	u64 lba, zs_lba;
+	u64 arr_len;
 	u8 *arr = NULL, *desc;
 	u8 *cmd = scp->cmnd;
 	struct sdeb_zone_state *zsp = NULL;
@@ -5911,9 +5912,11 @@ static int resp_report_zones(struct scsi_cmnd *scp,
 		return check_condition_result;
 	}
 
-	rep_max_zones = (alloc_len - 64) >> ilog2(RZONES_DESC_HD);
+	rep_max_zones = (ALIGN((u64)alloc_len, RZONES_DESC_HD) - RZONES_DESC_HD) >>
+			ilog2(RZONES_DESC_HD);
+	arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1);
 
-	arr = kzalloc(alloc_len, GFP_ATOMIC | __GFP_NOWARN);
+	arr = kzalloc(arr_len, GFP_ATOMIC | __GFP_NOWARN);
 	if (!arr) {
 		mk_sense_buffer(scp, ILLEGAL_REQUEST, INSUFF_RES_ASC,
 				INSUFF_RES_ASCQ);
-- 
2.50.1 (Apple Git-155)
Re: [PATCH v3] scsi: scsi_debug: fix REPORT ZONES alloc_len underflow OOB write
Posted by Damien Le Moal 2 weeks, 1 day ago 
On 7/10/26 14:57, Ibrahim Hashimov wrote:
> resp_report_zones() derives the number of zone descriptors that fit in
> the reply buffer from the command allocation length:
> 
> 	rep_max_zones = (alloc_len - 64) >> ilog2(RZONES_DESC_HD);
> 
> 	arr = kzalloc(alloc_len, GFP_ATOMIC | __GFP_NOWARN);
> 
> alloc_len is taken directly from the CDB and is fully controlled by the
> initiator. When alloc_len is smaller than the 64-byte report header
> (RZONES_DESC_HD), the subtraction underflows and rep_max_zones becomes a
> huge value. The buffer is then allocated with only alloc_len bytes, which
> is smaller than the 64-byte header the code unconditionally writes, and
> the descriptor loop is bounded by the bogus rep_max_zones. Both the header
> store and the following zone descriptors are then written past the end of
> the undersized allocation, corrupting adjacent slab memory.
> 
> Fix it by sizing the buffer to a whole number of 64-byte blocks that
> cover the requested allocation length:
> 
> 	rep_max_zones =
> 		(ALIGN((u64)alloc_len, RZONES_DESC_HD) - RZONES_DESC_HD)
> 		>> ilog2(RZONES_DESC_HD);
> 	arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1);
> 
> 	arr = kzalloc(arr_len, GFP_ATOMIC | __GFP_NOWARN);
> 
> RZONES_DESC_HD is a power of two, so ALIGN() rounds alloc_len up to the
> next multiple of 64 and rep_max_zones can no longer underflow: for any
> alloc_len of 1 to 64 it is 0, so only the header is built. arr_len is
> always RZONES_DESC_HD * (rep_max_zones + 1), which is exactly large enough
> for the header plus every descriptor the loop may write, so the report is
> always assembled within bounds, including a possibly partial trailing
> zone descriptor. The existing copy-out still transfers only what the host
> asked for:
> 
> 	fill_from_dev_buffer(scp, arr, min_t(u32, alloc_len, rep_len));
> 
> so an allocation length that ends in the middle of a zone descriptor
> returns the correctly truncated partial descriptor, as permitted by the
> SCSI/ZBC specifications, while never reading past arr_len.
> 
> The aligned length and the buffer size are computed in 64-bit (alloc_len
> is cast to u64 before ALIGN and the size product uses a u64 block size) so
> a crafted allocation length near U32_MAX cannot wrap them to a small value;
> such a request simply fails the large allocation and returns a check
> condition instead of overflowing the buffer.
> 
> This was found by static analysis. A KASAN slab-out-of-bounds runtime
> reproduction of the original underflow is being re-run against the ALIGN
> based fix and will be reported separately.
> 
> Fixes: 7db0e0c8190a ("scsi: scsi_debug: Fix buffer size of REPORT ZONES command")
> Suggested-by: Damien Le Moal <dlemoal@kernel.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
> Assisted-by: AuditCode-AI:2026.07

Looks OK to me.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research
[PATCH v4] scsi: scsi_debug: fix REPORT ZONES alloc_len underflow OOB write
Posted by Ibrahim Hashimov 1 week, 6 days ago 
resp_report_zones() sizes the reply buffer from the CDB allocation
length. The v3 fix rounds alloc_len up with ALIGN() before deriving the
descriptor count:

	rep_max_zones = (ALIGN((u64)alloc_len, RZONES_DESC_HD) -
			 RZONES_DESC_HD) >> ilog2(RZONES_DESC_HD);
	arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1);

For alloc_len in 0xFFFFFFC1..0xFFFFFFFF, ALIGN() rounds up to
0x100000000, so arr_len is 4 GB. On 32-bit, kzalloc()'s size_t is
32-bit and truncates 0x100000000 to 0; kzalloc(0) returns
ZERO_SIZE_PTR, which passes the !arr check, and desc = arr + 64 is then
dereferenced in the loop -> out-of-bounds write / panic.

Clamp rep_max_zones to devip->nr_zones. The loop already stops at
sdebug_capacity (after nr_zones zones), so a report can never hold more
than nr_zones descriptors; the clamp does not change the report, it
only bounds arr_len to (nr_zones + 1) * RZONES_DESC_HD, a real device
property that can never reach 0x100000000.

Fixes: 7db0e0c8190a ("scsi: scsi_debug: Fix buffer size of REPORT ZONES command")
Suggested-by: Damien Le Moal <dlemoal@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
Assisted-by: AuditCode-AI:2026.07
---
v4: clamp rep_max_zones to the device zone count (devip->nr_zones) so arr_len
cannot reach 0x100000000 and be truncated by kzalloc()'s 32-bit size_t on
32-bit platforms (which returns ZERO_SIZE_PTR and bypasses the NULL check),
as reported by sashiko-bot / Bart Van Assche on v3. This restores a bound
that pre-dated the loop refactor: the original REPORT ZONES code already
capped rep_max_zones at the device zone count. The clamp is additive and does
not change any report (the loop already stops at sdebug_capacity), so it only
bounds the allocation. Dropped Damien's v3 Reviewed-by since v4 adds a
functional line he has not reviewed; his ALIGN sizing is otherwise unchanged.
v3: https://lore.kernel.org/linux-scsi/20260710055755.53830-1-security@auditcode.ai/
 drivers/scsi/scsi_debug.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 9d1c9c41d0f9..643051332132 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -5890,6 +5890,7 @@ static int resp_report_zones(struct scsi_cmnd *scp,
 	u32 alloc_len, rep_opts, rep_len;
 	bool partial;
 	u64 lba, zs_lba;
+	u64 arr_len;
 	u8 *arr = NULL, *desc;
 	u8 *cmd = scp->cmnd;
 	struct sdeb_zone_state *zsp = NULL;
@@ -5911,9 +5912,12 @@ static int resp_report_zones(struct scsi_cmnd *scp,
 		return check_condition_result;
 	}
 
-	rep_max_zones = (alloc_len - 64) >> ilog2(RZONES_DESC_HD);
+	rep_max_zones = (ALIGN((u64)alloc_len, RZONES_DESC_HD) - RZONES_DESC_HD) >>
+			ilog2(RZONES_DESC_HD);
+	rep_max_zones = min_t(unsigned int, rep_max_zones, devip->nr_zones);
+	arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1);
 
-	arr = kzalloc(alloc_len, GFP_ATOMIC | __GFP_NOWARN);
+	arr = kzalloc(arr_len, GFP_ATOMIC | __GFP_NOWARN);
 	if (!arr) {
 		mk_sense_buffer(scp, ILLEGAL_REQUEST, INSUFF_RES_ASC,
 				INSUFF_RES_ASCQ);
-- 
2.50.1 (Apple Git-155)
Re: [PATCH v4] scsi: scsi_debug: fix REPORT ZONES alloc_len underflow OOB write
Posted by Bart Van Assche 1 week, 5 days ago 
On 7/12/26 11:37 AM, Ibrahim Hashimov wrote:
> Clamp rep_max_zones to devip->nr_zones. The loop already stops at
> sdebug_capacity (after nr_zones zones), so a report can never hold more
> than nr_zones descriptors; the clamp does not change the report, it
> only bounds arr_len to (nr_zones + 1) * RZONES_DESC_HD, a real device
> property that can never reach 0x100000000.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Re: [PATCH v4] scsi: scsi_debug: fix REPORT ZONES alloc_len underflow OOB write
Posted by Damien Le Moal 1 week, 5 days ago 
On 7/13/26 03:37, Ibrahim Hashimov wrote:
> resp_report_zones() sizes the reply buffer from the CDB allocation
> length. The v3 fix rounds alloc_len up with ALIGN() before deriving the
> descriptor count:
> 
> 	rep_max_zones = (ALIGN((u64)alloc_len, RZONES_DESC_HD) -
> 			 RZONES_DESC_HD) >> ilog2(RZONES_DESC_HD);
> 	arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1);
> 
> For alloc_len in 0xFFFFFFC1..0xFFFFFFFF, ALIGN() rounds up to
> 0x100000000, so arr_len is 4 GB. On 32-bit, kzalloc()'s size_t is
> 32-bit and truncates 0x100000000 to 0; kzalloc(0) returns
> ZERO_SIZE_PTR, which passes the !arr check, and desc = arr + 64 is then
> dereferenced in the loop -> out-of-bounds write / panic.
> 
> Clamp rep_max_zones to devip->nr_zones. The loop already stops at
> sdebug_capacity (after nr_zones zones), so a report can never hold more
> than nr_zones descriptors; the clamp does not change the report, it
> only bounds arr_len to (nr_zones + 1) * RZONES_DESC_HD, a real device
> property that can never reach 0x100000000.
> 
> Fixes: 7db0e0c8190a ("scsi: scsi_debug: Fix buffer size of REPORT ZONES command")
> Suggested-by: Damien Le Moal <dlemoal@kernel.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
> Assisted-by: AuditCode-AI:2026.07

Looks good.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research

Patchew 2.1-devel-ea86937

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