In shiftfs, a non-upstream patch to the Linux kernel included in the Ubuntu 5.0 and 5.3 kernel series, shiftfs_btrfs_ioctl_fd_replace() installs an fd referencing a file from the lower filesystem without taking an additional reference to that file. After the btrfs ioctl completes this fd is closed, which then puts a reference to that file, leading to a refcount underflow.
The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Linux_kernel | Linux | 5.0 (including) | 5.0 (including) |
| Linux_kernel | Linux | 5.3 (including) | 5.3 (including) |