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vfs: keep each loaded memfd image open until exit - #67068
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On Linux an addon or FFI library inside a VFS is loaded from an anonymous memfd through /proc/self/fd/N, and the memfd was closed right after a successful load. The next image then got the same fd number, hence the same path, and the dynamic loader, which knows a loaded object by the path it was opened with, returned the object already loaded under that path instead of loading the new file. So the second of any two addons or libraries loaded from a VFS resolved to the first: an addon after an FFI library failed with "Module did not self-register", an FFI library after an addon had none of its own symbols, and two addons silently became the same one. Keep a memfd open for the life of the process once it has been loaded, so no two images ever share a path; MFD_CLOEXEC keeps it out of child processes. A failed load still closes its memfd. The temp-file fallback is unaffected: each image there gets a fresh mkdtemp() directory, and Windows already keeps its images until exit. Signed-off-by: Philipp Dunkel <pip@pipobscure.com>
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #67068 +/- ##
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- Coverage 90.65% 90.65% -0.01%
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Files 797 797
Lines 278268 278320 +52
Branches 53517 53535 +18
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+ Hits 252261 252305 +44
- Misses 16386 16397 +11
+ Partials 9621 9618 -3
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On Linux an addon or FFI library inside a VFS is loaded from an anonymous memfd through /proc/self/fd/N, and the memfd was closed right after a successful load. The next image then got the same fd number, hence the same path, and the dynamic loader, which knows a loaded object by the path it was opened with, returned the object already loaded under that path instead of loading the new file. So the second of any two addons or libraries loaded from a VFS resolved to the first: an addon after an FFI library failed with "Module did not self-register", an FFI library after an addon had none of its own symbols, and two addons silently became the same one.
Keep a memfd open for the life of the process once it has been loaded, so no two images ever share a path; MFD_CLOEXEC keeps it out of child processes. A failed load still closes its memfd. The temp-file fallback is unaffected: each image there gets a fresh mkdtemp() directory, and Windows already keeps its images until exit.