qlcnic: prevent ->dcb use-after-free on qlcnic_dcb_enable() failure

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: qlcnic: prevent ->dcb use-after-free on qlcnic_dcb_enable() failure adapter->dcb would get silently freed inside qlcnic_dcb_enable() in case qlcnic_dcb_attach() would return an error, which always happens under OOM conditions. This would lead to use-after-free because both of the existing callers invoke qlcnic_dcb_get_info() on the obtained pointer, which is potentially freed at that point. Propagate errors from qlcnic_dcb_enable(), and instead free the dcb pointer at callsite using qlcnic_dcb_free(). This also removes the now unused qlcnic_clear_dcb_ops() helper, which was a simple wrapper around kfree() also causing memory leaks for partially initialized dcb. Found by Linux Verification Center (linuxtesting.org) with the SVACE static analysis tool.

References

• https://git.kernel.org/stable/c/36999236f0b12d5de21a6f40e93b570727b9ceb2
• https://git.kernel.org/stable/c/d12a7510293d3370b234b0b7c5eda33e58786768
• https://git.kernel.org/stable/c/8f97eeb02a553cdc78c83a0596448a370e1518c4
• https://git.kernel.org/stable/c/513787ff9a331b461115e8a145a983d650a84fcb
• https://git.kernel.org/stable/c/95df720e64a6409d8152827a776c43f615e3321a
• https://git.kernel.org/stable/c/8df1dc04ce0e4c03b51a756749c250a9cb17d707
• https://git.kernel.org/stable/c/a2a694e6edbdb3efb34e1613a31fdcf6cf444a55
• https://git.kernel.org/stable/c/13a7c8964afcd8ca43c0b6001ebb0127baa95362