Fix out-of-bounds reads in cmap format-12 and kern format-0 parsers#45
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ChakshuGupta13 wants to merge 1 commit into
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Fix out-of-bounds reads in cmap format-12 and kern format-0 parsers#45ChakshuGupta13 wants to merge 1 commit into
ChakshuGupta13 wants to merge 1 commit into
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Add missing validation that the declared entry count fits within the subtable data for cmap format-12/13 (numGroups) and kern format-0 (numPairs). Without these checks, a malformed font can cause reads past the end of the font buffer. Both checks use the already-validated subtable length to avoid integer overflow. No effect on well-formed fonts.
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Closes #44.
Adds two missing bounds checks:
cmap format-12/13 (
cmap_fmt12_13): validates that the declarednumGroupsfits within the subtablelenbefore the group-reading loop. Without this, a malformed font withnumGroupslarger than the actual subtable data causes reads past the font buffer. The existingcmap_fmt6function already has the analogous check.kern format-0 (
sft_kerning): validates thatnumPairs * 6fits within the font before passingnumPairstobsearch.Both checks use the already-validated subtable length (or
is_safe_offset) to avoid integer overflow. No behavioral change for well-formed fonts.Verified with AddressSanitizer: a crafted 178-byte PoC font that previously triggered a heap-buffer-overflow read now returns cleanly. Valid fonts (Ubuntu, FiraGO, Noto families) are unaffected.