Re: [PATCH 1/2] dma-mapping: benchmark: fix up kthread creation error handling

From: Robin Murphy
Date: Fri May 03 2024 - 08:30:11 EST


On 2024-05-02 5:18 pm, Fedor Pchelkin wrote:
If a kthread creation fails for some reason then uninitialized members of
the tasks array will be accessed on the error path since it is allocated
by kmalloc_array().

Limit the bound in such case.

I don't think this is right... The put_task_struct() calls on the error path are supposed to balance the get_task_struct() calls which only happen *after* all the threads are successfully created - see commit d17405d52bac ("dma-mapping: benchmark: fix kernel crash when dma_map_single fails") - although I now wonder whether that might have been better done by replacing kthread_stop() with kthread_stop_put(). It doesn't look like we've ever actually tried to free any previous threads from the point of allocation failure.

Thanks,
Robin.

Found by Linux Verification Center (linuxtesting.org).

Fixes: 65789daa8087 ("dma-mapping: add benchmark support for streaming DMA APIs")
Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
---
kernel/dma/map_benchmark.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/dma/map_benchmark.c b/kernel/dma/map_benchmark.c
index 02205ab53b7e..ea938bc6c7e3 100644
--- a/kernel/dma/map_benchmark.c
+++ b/kernel/dma/map_benchmark.c
@@ -118,6 +118,7 @@ static int do_map_benchmark(struct map_benchmark_data *map)
if (IS_ERR(tsk[i])) {
pr_err("create dma_map thread failed\n");
ret = PTR_ERR(tsk[i]);
+ threads = i;
goto out;
}