CVE-2021-47282: 
Linux Debian vulnerability analysis and mitigation

In the Linux kernel, a vulnerability has been identified in the bcm2835 SPI driver where an out-of-bounds access could occur when using more than 4 slaves. The issue was introduced by commit 571e31fa60b3 which limited the number of slaves to 3 at compile-time through a statically-sized array prepare_cs[] in the driver private data (Kernel Commit).

The vulnerability stems from the driver's attempt to enforce a limitation on the number of chipselects by setting the controller's num_chipselect to 3. However, when GPIO chipselects are specified in the device tree for more than 3 slaves, num_chipselect is silently raised by of_spi_get_gpio_numbers(), resulting in out-of-bounds accesses to the statically-sized array prepare_cs[] (Kernel Commit).

The vulnerability could lead to out-of-bounds memory access when using more than 4 SPI slaves with the bcm2835 SPI driver, potentially causing system instability or crashes (Kernel Commit).

The issue has been fixed by raising the number of allowed slaves to 24 as a temporary solution, enforcing the limitation on slave setup, and reverting num_chipselect to 3 (which is the number of native chipselects supported by the controller). Users are advised to update to patched kernel versions that include this fix (Kernel Commit).