Bug 219106 - udmabuf allows creating write mapping for write-sealed memfd
Summary: udmabuf allows creating write mapping for write-sealed memfd
Status: NEW
Alias: None
Product: Linux
Classification: Unclassified
Component: Kernel (show other bugs)
Hardware: All Linux
: P3 normal
Assignee: Virtual assignee for kernel bugs
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Depends on:
Blocks:
 
Reported: 2024-07-30 05:56 UTC by Julian Orth
Modified: 2024-12-03 17:32 UTC (History)
1 user (show)

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Regression: No
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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/ .
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