fix(cutils): handle vsnprintf encoding error in dbuf_printf#1482
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andreasrosdal wants to merge 1 commit into
Open
fix(cutils): handle vsnprintf encoding error in dbuf_printf#1482andreasrosdal wants to merge 1 commit into
andreasrosdal wants to merge 1 commit into
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When vsnprintf returns -1 (encoding error - e.g. an %ls conversion that hits an invalid multibyte sequence), dbuf_printf's slow path advanced s->size by len = -1, wrapping the size_t to ~SIZE_MAX. Subsequent dbuf operations then treated the buffer as essentially unlimited and indexed off the end. Bail out, flag the buffer as errored, and let callers propagate. No automated test: dbuf_printf is internal and reaching the vsnprintf encoding-error branch requires either an invalid multibyte input to %ls (locale-dependent and not portable) or a vsnprintf implementation that returns -1 for other reasons. Reviewed by inspection.
bnoordhuis
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May 17, 2026
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| if (len < 0) { | ||
| /* vsnprintf encoding error: don't let the caller wrap s->size by | ||
| advancing it by -1, which would underflow to near SIZE_MAX. */ | ||
| s->error = true; | ||
| return -1; | ||
| } |
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Maybe this should just be an assert? I'm trying to think of a scenario where len < 0 could happen that is not a bug on our side, but I can't come up with anything.
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Agreed, this is not exposed to user code to it must be an internal one, so let's assert on it.
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When vsnprintf returns -1 (encoding error - e.g. an %ls conversion that hits an invalid multibyte sequence), dbuf_printf's slow path advanced s->size by len = -1, wrapping the size_t to ~SIZE_MAX. Subsequent dbuf operations then treated the buffer as essentially unlimited and indexed off the end.
Bail out, flag the buffer as errored, and let callers propagate.
No automated test: dbuf_printf is internal and reaching the vsnprintf encoding-error branch requires either an invalid multibyte input to %ls (locale-dependent and not portable) or a vsnprintf implementation that returns -1 for other reasons. Reviewed by inspection.