MFC r317707:

Correct an out-of-bounds read in regcomp when the RE is bad.

When passed the invalid regular expression "a**", the error is
eventually detected and seterr() is called. It sets p->error
appropriatly and p->next and p->end to nuls which is a never used char
nuls[10] which is zeros due to .bss initialization. Unfortunatly,
p_ere_exp() and p_simp_re() both have fall through cases where they set
the error, decrement p->next and access it which means a read from
whatever .bss variable comes before nuls.

Found with regex_test:repet_multi and CHERI bounds checking.

Reviewed by:	ngie, pfg, emaste
Obtained from:	CheriBSD
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D10541

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/libc/regex/regcomp.c b/lib/libc/regex/regcomp.c
index 9211f65..1e231fb 100644
--- a/lib/libc/regex/regcomp.c
+++ b/lib/libc/regex/regcomp.c
@@ -444,6 +444,8 @@ p_ere_exp(struct parse *p)
 		(void)REQUIRE(!MORE() || !isdigit((uch)PEEK()), REG_BADRPT);
 		/* FALLTHROUGH */
 	default:
+		if (p->error != 0)
+			return;
 		p->next--;
 		wc = WGETNEXT();
 		ordinary(p, wc);
@@ -651,6 +653,8 @@ p_simp_re(struct parse *p,
 		(void)REQUIRE(starordinary, REG_BADRPT);
 		/* FALLTHROUGH */
 	default:
+		if (p->error != 0)
+			return(0);	/* Definitely not $... */
 		p->next--;
 		wc = WGETNEXT();
 		ordinary(p, wc);