Fix GH-19320: Prevent FPM UID and GID overflow - #22986
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bukka
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Aug 2, 2026
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The logic makes sense to me. Just not sure about that shift if it's safe. If someone could re-check that would be great.
| { | ||
| uintmax_t max = (uid_t) -1 > (uid_t) 0 | ||
| ? (uintmax_t) ((uid_t) -2) | ||
| : (UINTMAX_C(1) << (sizeof(uid_t) * CHAR_BIT - 1)) - 1; |
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This should someone re-check but couldn't that shift be in some cases undefined (e.g. on 32bit)?
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I re-checked this. UINTMAX_C(1) makes the left operand an unsigned uintmax_t, so on a 32-bit system this is a shift by 31 and is defined. uintmax_t is required to be able to represent any unsigned integer type, and this branch is only used when uid_t is signed. So this should be safe here, but I can add a short comment if you think it would make the intent clearer.
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FPM parses numeric
user,group,listen.owner, andlisten.groupvalues withstrtoul(), but stores them in signedintfields. That can silently change an ID before it reachessetuid(),setgid(), orchown().This stores the values in
uid_t/gid_tand rejects IDs that the platform types cannot represent during config validation. It also rejects the all-bits-one value used bychown()as its no-change sentinel.I added coverage for all four numeric directives and ran the full FPM test suite.
Fixes GH-19320