From 436584a4302b1c6da55080c0a0408a98e551ea7e Mon Sep 17 00:00:00 2001 From: "Arnold D. Robbins" Date: Mon, 6 Apr 2026 10:56:38 +0300 Subject: [PATCH] Add overflow checking in do_sub for 32 bit systems. CVE: CVE-2026-40469 Upstream-Status: Backport [https://cgit.git.savannah.gnu.org/cgit/gawk.git/commit/?id=aa7272a6e1184cdd21ab8f89200219abd8053eda] (cherry picked from commit aa7272a6e1184cdd21ab8f89200219abd8053eda) Signed-off-by: Darsh Kelaiya --- ChangeLog | 9 +++++++++ builtin.c | 25 ++++++++++++++++++++----- 2 files changed, 29 insertions(+), 5 deletions(-) diff --git a/ChangeLog b/ChangeLog index 8cdf90f6..c1b2e7f4 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,12 @@ +2026-04-06 Arnold D. Robbins + + * builtin.c (do_sub): Check for overflow in calculation of size + of result buffer by doing the math in 64 bits. This provides + a fatal message on 32 bit systems if overflow happens instead + of letting dynamic memory get corrupted and likely causing + a core dump. Thanks to Michał Majchrowicz + for the report and fix. + 2026-04-04 Arnold D. Robbins * builtin.c (do_sub): Make `sofar' be size_t to avoid diff --git a/builtin.c b/builtin.c index d0e083da..3906d507 100644 --- a/builtin.c +++ b/builtin.c @@ -1820,11 +1820,13 @@ do_sub(int nargs, unsigned int flags) bool lastmatchnonzero; char *mb_indices = NULL; int searchflags = RE_NEED_START; + const char *fname = NULL; // for fatal message, below if ((flags & GENSUB) != 0) { double d; NODE *glob_flag; + fname = "gensub"; check_exact_args(nargs, "gensub", 4); tmp = PEEK(3); @@ -1856,11 +1858,9 @@ do_sub(int nargs, unsigned int flags) DEREF(glob_flag); searchflags |= RE_NEED_SUB; } else { - if ((flags & GSUB) != 0) { - check_exact_args(nargs, "gsub", 3); - } else { - check_exact_args(nargs, "sub", 3); - } + fname = ((flags & GSUB) != 0) ? "gsub" : "sub"; + + check_exact_args(nargs, fname, 3); /* take care of regexp early, in case re_update is fatal */ @@ -1976,6 +1976,21 @@ do_sub(int nargs, unsigned int flags) * vary since ampersand is actual text of regexp match. */ + // 4/2026: This overflow check simply provides a fatal + // message instead of letting realloc() die later after + // a buffer overrun. It simply makes the user experience better, + // but does not prevent gawk from dying miserably. I suppose + // it's worth the trouble, but just barely. + + /* uint64_t so the product is 64-bit even on 32-bit ILP32 builds */ + uint64_t repl_contribution = + (uint64_t)(unsigned int)ampersands + * (uint64_t)(uintptr_t)(matchend - matchstart); + if (repl_contribution > (uint64_t)SIZE_MAX + || repl_contribution > (uint64_t)SIZE_MAX - (size_t)(matchend - text) + - repllen - 1) + fatal(_("%s: replacement expansion too large"), fname); + /* * add 1 to len to handle "empty" case where * matchend == matchstart and we force a match on a single -- 2.53.0