Derive the lolor.node bound from the OID encoding. - #53
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Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe changes add tests for large-object function privileges and ChangesLarge-Object Function Privilege Coverage
OID Node Bounds
Priority: ➖ Normal Merge Risk: 🟠 High · up to Some databases already running 1.3.0 may retain PUBLIC access to the file-related functions, with no current extension upgrade to remove it. Address that upgrade gap before merging. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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I see that the README promises much more:
"You must set the lolor.node parameter before using the extension. The value can be from 1 to 2^28; the value is used to help in generation of new large object OID."
I think, it should be fixed with this PR.
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| ## lolor 1.4.0 | |||
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| * **Security fix: `lo_import()` and `lo_export()` were executable by any database user.** These functions read and write files on the server as the operating system account PostgreSQL runs under, and core revokes `EXECUTE` on them from `PUBLIC`. lolor replaces them by renaming the originals to `*_orig`; an ACL belongs to a function rather than to a name, so the restriction stayed behind on the parked original while each replacement was created with the default of `EXECUTE TO PUBLIC`. Any user could therefore read an arbitrary server file with `lo_import()` or overwrite one with `lo_export()`. The replacements are now locked down at install time, and the upgrade to 1.4.0 revokes the privilege on existing installations in either the enabled or the disabled state. All versions from 1.0 through 1.3.0 are affected. | |||
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What if someone has 16 already?
I think release notes should warn about that.
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Good catch, warning added in f6e4c39.
I checked what actually happens. The server still starts, logs 16 is outside the valid range for parameter "lolor.node" (0 .. 15) once, and falls back to 0.
Falling back to 0 costs nothing, because 16 never encoded as 16. It is ORed into a 4 bit field, so the node bits came out as 0 and bit 4 of the OID got forced to 1. Confirmed on the old build:
oid1 | node_field_1
--------+--------------
348112 | 0
So anyone running 16 has been generating node 0 OIDs all along. The real risk is not the upgrade, it is that they collide with whichever node is genuinely 0. The note now says to pick a value in 0..15 and check for collisions against that node.
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Inline comments:
In `@README.md`:
- Around line 120-121: Add a new versioned update from 1.3.0 that revokes PUBLIC
EXECUTE on all three replacement function signatures, and set the extension
target to that version. In README.md lines 120–121, name the new version as the
security fix; in docs/lolor_release_notes.md line 11, also identify previously
installed 1.3.0 systems as affected.
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A generated large object OID reserves four bits for the node id, but the GUC accepted 0..16. Node 16 does not fit and was silently encoded as node 0, so two nodes could generate colliding OIDs. Move the encoding parameters into lolor.h and compute the GUC maximum from them, so the bound cannot drift from the layout it protects.
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A generated large object OID keeps the node id in its low four bits, but
lolor.nodeaccepted 0..16. Node 16 does not fit: the node field came out as 0, so it could collide with a real node 0.The bound and the encoding were defined separately in two files. This moves the encoding into
lolor.hand derives the GUC maximum from it, so they cannot drift again.SET lolor.node = 16is now rejected with the valid range 0..15.No change for valid settings; the
MAX_NODEID_BITS/MAX_OID_BITSchange is a rename. The release notes say what happens to an install that already has 16 configured: the server still starts, logs a warning, and falls back to 0, which is what 16 was effectively using anyway.