CVE-2019-15792

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() calls fdget(oldfd), then without further checks passes the resulting file* into shiftfs_real_fdget(), which casts file->private_data, a void* that points to a filesystem-dependent type, to a struct shiftfs_file_info *. As the private_data is not required to be a pointer, an attacker can use this to cause a denial of service or possibly execute arbitrary code.

Weakness

The product allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.

Affected Software

Extended Description

When the product accesses the resource using an incompatible type, this could trigger logical errors because the resource does not have expected properties. In languages without memory safety, such as C and C++, type confusion can lead to out-of-bounds memory access. While this weakness is frequently associated with unions when parsing data with many different embedded object types in C, it can be present in any application that can interpret the same variable or memory location in multiple ways. This weakness is not unique to C and C++. For example, errors in PHP applications can be triggered by providing array parameters when scalars are expected, or vice versa. Languages such as Perl, which perform automatic conversion of a variable of one type when it is accessed as if it were another type, can also contain these issues.

References

• https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/eoan/commit/?id=5df147c8140efc71ac0879ae3b0057f577226d4c
• https://usn.ubuntu.com/usn/usn-4183-1
• https://usn.ubuntu.com/usn/usn-4184-1