CVE-2019-15794: Reference counting error in overlayfs/shiftfs error path when used in conjuction with aufs

Vulnerability summary

CVE-2019-15794 is a high (CVSS 7.2) vulnerability in canonical ubuntu_linux. EPSS estimates a 1.16% chance of exploitation in the next 30 days, higher than 67.1% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 23-04-2020
   PublishedVulnerability first disclosed.
2. 16-09-2024
   Last modifiedVulnerability information updated.

Description

Overlayfs in the Linux kernel and shiftfs, a non-upstream patch to the Linux kernel included in the Ubuntu 5.0 and 5.3 kernel series, both replace vma->vm_file in their mmap handlers. On error the original value is not restored, and the reference is put for the file to which vm_file points. On upstream kernels this is not an issue, as no callers dereference vm_file following after call_mmap() returns an error. However, the aufs patchs change mmap_region() to replace the fput() using a local variable with vma_fput(), which will fput() vm_file, leading to a refcount underflow.

• CWE-672Operation on a Resource after Expiration or ReleaseThe product uses, accesses, or otherwise operates on a resource after that resource has been expired, released, or revoked.