Bug 219106

Summary: udmabuf allows creating write mapping for write-sealed memfd
Product: Linux Reporter: Julian Orth (ju.orth)
Component: KernelAssignee: Virtual assignee for kernel bugs (linux-kernel)
Status: NEW ---    
Severity: normal CC: jannh
Priority: P3    
Hardware: All   
OS: Linux   
Kernel Version: Subsystem:
Regression: No Bisected commit-id:

Description Julian Orth 2024-07-30 05:56:58 UTC 
udmabuf

1. checks that the memfd does not have a write seal
2. makes it so that no write seal can be added in the future

But these two steps are not atomic and userspace can add a seal in between. Userspace can then map the dmabuf to get write access to the memfd.

POC: https://github.com/mahkoh/udmabuf-seal

Requires the user to have read access to /dev/udmabuf.

Tested with 6.10.1 and 6.11-rc1.
Comment 1 Jann Horn (Google) 2024-12-03 17:32:04 UTC 
I posted a patch for this at https://lore.kernel.org/all/20241203-udmabuf-fixes-v1-1-f99281c345aa@google.com/ .