CVE-2024-49987: bpftool: Fix undefined behavior in qsort(NULL, 0, ...)

In the Linux kernel, the following vulnerability has been resolved:

bpftool: Fix undefined behavior in qsort(NULL, 0, ...)

When netfilter has no entry to display, qsort is called with qsort(NULL, 0, ...). This results in undefined behavior, as UBSan reports:

net.c:827:2: runtime error: null pointer passed as argument 1, which is declared to never be null

Although the C standard does not explicitly state whether calling qsort with a NULL pointer when the size is 0 constitutes undefined behavior, Section 7.1.4 of the C standard (Use of library functions) mentions:

"Each of the following statements applies unless explicitly stated otherwise in the detailed descriptions that follow: If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer, or a pointer to non-modifiable storage when the corresponding parameter is not const-qualified) or a type (after promotion) not expected by a function with variable number of arguments, the behavior is undefined."

To avoid this, add an early return when nflinkinfo is NULL to prevent calling qsort with a NULL pointer.

— NVD

This CVE was automatically created from a reference found in an email or other text. If you are reading this, then this CVE entry is probably erroneous, since this text should be replaced by the official CVE description automatically.

— Launchpad