If we read in a line with \0 at the beginning, blen will be 0. However,
we then try to index our copy of the buffer with
s->lines[s->linecount][blen-1], we'll read (and potentially write if the
data happens to be 0x0A) outside of strdup's allocated memory, and may
crash.
Fix this by just rejecting lines with a leading \0. Lines with nulls
embedded in other places don't invoke similar behaviour, since the
length is still >0.
---
sent.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/sent.c b/sent.c
index c50a572..f9dcd75 100644
--- a/sent.c
+++ b/sent.c
@@ -428,6 +428,10 @@ load(FILE *fp)
maxlines = 0;
memset((s = &slides[slidecount]), 0, sizeof(Slide));
do {
+ /* if there's a leading null, we can't do blen-1 */
+ if (!*buf)
+ continue;
+
if (buf[0] == '#')
continue;
--
2.26.2
