char: applicom: fix NULL pointer dereference in ac_ioctl

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: char: applicom: fix NULL pointer dereference in ac_ioctl Discovered by Atuin - Automated Vulnerability Discovery Engine. In ac_ioctl, the validation of IndexCard and the check for a valid RamIO pointer are skipped when cmd is 6. However, the function unconditionally executes readb(apbs[IndexCard].RamIO + VERS) at the end. If cmd is 6, IndexCard may reference a board that does not exist (where RamIO is NULL), leading to a NULL pointer dereference. Fix this by skipping the readb access when cmd is 6, as this command is a global information query and does not target a specific board context.

References

• https://git.kernel.org/stable/c/5a6240804fb7bbd4f5f6e706955248a6f4c1abbc
• https://git.kernel.org/stable/c/d1b0452280029d05a98c75631131ee61c0b0d084
• https://git.kernel.org/stable/c/0b8b353e09888bccee405e0dd6feafb60360f478
• https://git.kernel.org/stable/c/d285517429a75423789e6408653e57b6fdfc8e54
• https://git.kernel.org/stable/c/74883565c621eec6cd2e35fe6d27454cf2810c23
• https://git.kernel.org/stable/c/f83e3e9f89181b42f6076a115d767a7552c4a39e
• https://git.kernel.org/stable/c/82d12088c297fa1cef670e1718b3d24f414c23f7