rcu: Fix buffer overflow in print_cpu_stall_info()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: rcu: Fix buffer overflow in print_cpu_stall_info() The rcuc-starvation output from print_cpu_stall_info() might overflow the buffer if there is a huge difference in jiffies difference. The situation might seem improbable, but computers sometimes get very confused about time, which can result in full-sized integers, and, in this case, buffer overflow. Also, the unsigned jiffies difference is printed using %ld, which is normally for signed integers. This is intentional for debugging purposes, but it is not obvious from the code. This commit therefore changes sprintf() to snprintf() and adds a clarifying comment about intention of %ld format. Found by Linux Verification Center (linuxtesting.org) with SVACE.

References

• https://git.kernel.org/stable/c/e2228ed3fe7aa838fba87c79a76fb1ad9ea47138
• https://git.kernel.org/stable/c/afb39909bfb5c08111f99e21bf5be7505f59ff1c
• https://git.kernel.org/stable/c/9351e1338539cb7f319ffc1210fa9b2aa27384b5
• https://git.kernel.org/stable/c/4c3e2ef4d8ddd313c8ce3ac30505940bea8d6257
• https://git.kernel.org/stable/c/3758f7d9917bd7ef0482c4184c0ad673b4c4e069