[PATCH 6/6] diff: use size_t in count_trailing_blank()

Since 3c7a31204f (xdiff: use size_t for buffer sizes, 2026-09-30), mmfile_t stores its size as a size_t, but count_trailing_blank() still copies it into a "long". On platforms where "long" is 32 bits wide, like Windows, a buffer between 2GiB and 4GiB gives a negative size, and "ptr += size - 1" points about 2GiB before the start of the buffer, which we then dereference.

check_blank_at_eof() calls this function whenever the whitespace rule includes blank-at-eof, which is the default, and it does so before xdi_diff() rejects inputs larger than MAX_XDIFF_SIZE. Large files are normally treated as binary and never get here, but a "diff" attribute or a textconv driver makes us diff them as text. A repository can ship such an attribute in its .gitattributes, so "git show" or "git log -p" on a commit adding a 3GiB file can be made to crash.

Use size_t; the rest of the function works unchanged with it.

No test, as triggering this needs a platform with a 32-bit "long" and a blob larger than 2GiB.

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
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 diff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)