plan9port

commit 3ccd61629b641613bcccbc51125330efab9c89a7
parent 6a80119eb509bd948d87ad1b84b0a82855a3c691
Author: Russ Cox <rsc@swtch.com>
Date:   Thu, 14 Jan 2021 10:05:50 -0500

sam: avoid out-of-bounds read in rterm

Usually r->nused < r->nalloc and the read is in bounds.
But it could in theory be right on the line and reading
past the end of the allocation.

Make it safe but preserve as much of the old semantics
as possible. This use of rterm appears to be only for
optimization purposes so the result does not matter
for correctness.

Diffstat:
M
src/cmd/sam/rasp.c
 | 
4
++--

1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/cmd/sam/rasp.c b/src/cmd/sam/rasp.c
@@ -283,8 +283,8 @@ rterm(List *r, Posn p1)
 
 	for(p = 0,i = 0; i<r->nused && p+L(i)<=p1; p+=L(i++))
 		;
-	if(i==r->nused && (i==0 || !T(i-1)))
-		return 0;
+	if(i==r->nused)
+		return i > 0 && T(i-1);
 	return T(i);
 }