From: David Lechner dlechner@baylibre.com
[ Upstream commit 5a2f15c5a8e017d0951e6dc62aa7b5b634f56881 ]
Fix overallocating the size of the scan buffer by converting bits to bytes. The size is meant to be in bytes, so scanbits needs to be divided by 8.
Signed-off-by: David Lechner dlechner@baylibre.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Reviewed-by: Nuno Sá nuno.sa@analog.com Link: https://patch.msgid.link/20250701-iio-adc-ad7173-add-spi-offload-support-v3-... Signed-off-by: Jonathan Cameron Jonathan.Cameron@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
**Backport Status: YES**
This commit fixes a clear memory overallocation bug in the ad_sigma_delta ADC driver that has been present since kernel v5.19. The analysis shows:
1. **Bug Description**: The code incorrectly calculates buffer size by treating `storagebits` (which is in bits) as if it were in bytes. The `storagebits` field in `struct iio_scan_type` represents the number of bits needed to store a sample, typically 8, 16, 24, or 32 bits.
2. **Impact**: The bug causes the driver to allocate 8x more memory than needed. For example: - If `storagebits = 16` (2 bytes per sample) and `slot = 4` - Buggy calculation: `ALIGN(4 * 16, 8) = 64 bytes` - Correct calculation: `ALIGN(4 * 16 / 8, 8) = 8 bytes`
This wastes kernel memory and could potentially lead to memory exhaustion in systems with many IIO devices.
3. **Fix Quality**: The fix is minimal and correct - simply dividing by 8 to convert bits to bytes. This is consistent with how `storagebits` is used throughout the IIO subsystem, as evidenced by the grep results showing `sizeof(u32) * 8` assignments.
4. **Affected Versions**: The bug was introduced in commit 8bea9af887de4 ("iio: adc: ad_sigma_delta: Add sequencer support") which first appeared in v5.19 and is present in all releases since then (v5.19, v6.0, v6.1, v6.10, v6.11).
5. **Stable Criteria Met**: - ✓ Fixes a real bug (memory overallocation) - ✓ Small, contained fix (single line change) - ✓ No architectural changes - ✓ Low risk of regression - ✓ Bug affects users (wastes memory) - ✓ Clear and obvious fix
The commit should be backported to all stable kernels from v5.19 onwards to fix this memory waste issue in the industrial I/O subsystem.
drivers/iio/adc/ad_sigma_delta.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c index 533667eefe41..71e775a10a91 100644 --- a/drivers/iio/adc/ad_sigma_delta.c +++ b/drivers/iio/adc/ad_sigma_delta.c @@ -378,7 +378,7 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev) return ret; }
- samples_buf_size = ALIGN(slot * indio_dev->channels[0].scan_type.storagebits, 8); + samples_buf_size = ALIGN(slot * indio_dev->channels[0].scan_type.storagebits / 8, 8); samples_buf_size += sizeof(int64_t); samples_buf = devm_krealloc(&sigma_delta->spi->dev, sigma_delta->samples_buf, samples_buf_size, GFP_KERNEL);