of: module: prevent NULL pointer dereference in vsnprintf()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: of: module: prevent NULL pointer dereference in vsnprintf() In of_modalias(), we can get passed the str and len parameters which would cause a kernel oops in vsnprintf() since it only allows passing a NULL ptr when the length is also 0. Also, we need to filter out the negative values of the len parameter as these will result in a really huge buffer since snprintf() takes size_t parameter while ours is ssize_t... Found by Linux Verification Center (linuxtesting.org) with the Svace static analysis tool.

References

• https://git.kernel.org/stable/c/e4a449368a2ce6d57a775d0ead27fc07f5a86e5b
• https://git.kernel.org/stable/c/544561dc56f7e69a053c25e11e6170f48bb97898
• https://git.kernel.org/stable/c/a1aa5390cc912934fee76ce80af5f940452fa987