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SubjectRe: [PATCH] stm class: Fix out of bound access from bitmap allocation
Sai Prakash Ranjan <> writes:

> From: Mulu He <>
> Bitmap allocation works on array of unsigned longs and
> for stm master allocation when the number of software
> channels is 32, 4 bytes are allocated and there is a out of
> bound access at the first 8 bytes access of bitmap region.

Does the below fix the problem for you?

From fb22b9ab109b332e58d72df13563e270befbd0e3 Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <>
Date: Tue, 16 Apr 2019 17:47:02 +0300
Subject: [PATCH] stm class: Fix channel bitmap on 32-bit systems

Commit 7bd1d4093c2f ("stm class: Introduce an abstraction for System Trace
Module devices") naively calculates the channel bitmap size in 64-bit
chunks regardless of the size of underlying unsigned long, making the
bitmap half as big on a 32-bit system. This leads to an out of bounds
access with the upper half of the bitmap.

Fix this by using BITS_TO_LONGS. While at it, convert to using
struct_size() for the total size calculation of the master struct.

Signed-off-by: Alexander Shishkin <>
Fixes: 7bd1d4093c2f ("stm class: Introduce an abstraction for System Trace Module devices")
Reported-by: Mulu He <>
Cc: # v4.4+
drivers/hwtracing/stm/core.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index 5b5807cbcf7c..8c45e79e47db 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -166,11 +166,9 @@ stm_master(struct stm_device *stm, unsigned int idx)
static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
struct stp_master *master;
- size_t size;

- size = ALIGN(stm->data->sw_nchannels, 8) / 8;
- size += sizeof(struct stp_master);
- master = kzalloc(size, GFP_ATOMIC);
+ master = kzalloc(struct_size(master, chan_map, BITS_TO_LONGS(stm->data->sw_nchannels)),
if (!master)
return -ENOMEM;

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