libshaderc_util: make DecodeLineDirective robust to a non-canonical #line prefix#1578
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adilburaksen wants to merge 1 commit into
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libshaderc_util: make DecodeLineDirective robust to a non-canonical #line prefix#1578adilburaksen wants to merge 1 commit into
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…refix GetShaderStageFromSourceCode checks for the "#line" prefix (five characters, without the trailing space) before calling DecodeLineDirective, whose local kLineDirective is "#line " (six characters) and which does substr(kLineDirective.size()). The precondition that the argument is a canonical "#line " directive was enforced only by an assert, which is compiled out in release builds, so a line equal to exactly "#line" would make string_piece::substr advance past the end of the piece. Verify the full canonical prefix at runtime and return early otherwise, so the release behavior matches the documented precondition regardless of the caller.
Collaborator
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Thanks for finding this! The real underyling problem is that there are two definitions of kLineDirective and they are out of sync. I'll fix this another way. |
dneto0
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Jul 8, 2026
Thanks to the implied bug report in #1578
Collaborator
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Fixed by #1579 instead |
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Description
Compiler::GetShaderStageFromSourceCodeguards withstarts_with("#line")— fivecharacters, no trailing space (
kLineDirective = "#line") — and then callsDecodeLineDirective, whose own localkLineDirectiveis"#line "(six characters)and which does
directive.substr(kLineDirective.size())==substr(6).DecodeLineDirective's documented precondition (a canonicalized#linedirective) isenforced only by
assert(directive.starts_with(kLineDirective)), which is compiled outunder
NDEBUG. A line equal to exactly"#line"(five characters) passes the caller'sfive-character check but is one character shorter than the six the callee consumes, so in
a release build
string_piece::substr(6)produces a piece whosebegin_ > end_(its ownbound is likewise an assert), after which
size()underflows.This is latent in practice because glslang's preprocessor rejects a bare
#linebeforethis code runs, so it is not a reachable defect via shader input — but the helper should
not silently rely on that. This change verifies the full canonical prefix at runtime and
returns early otherwise, so the release behavior matches the precondition regardless of
the caller. No functional change for well-formed
#line <n>directives.