Re: [PATCH 15/67] convert trivial sprintf / strcpy calls to xsnprintf

We sometimes sprintf into static buffers when we know that
the size of the buffer is large enough to fit the input
(either because it's a constant, or because it's numeric
input that is bounded in size). Likewise with strcpy of
constant strings.

However, these sites make it hard to audit sprintf and
strcpy calls for buffer overflows, as a reader has to
cross-reference the size of the array with the input. Let's
use xsnprintf instead, which communicates to a reader that
we don't expect this to overflow (and catches the mistake in
case we do).

Signed-off-by: Jeff King <redacted>
---

diff --git a/builtin/merge-index.c b/builtin/merge-index.c
index 1a1eafa..1d66111 100644
--- a/builtin/merge-index.c
+++ b/builtin/merge-index.c

@@ -23,7 +23,7 @@ static int merge_entry(int pos, const char *path)
                        break;
                found++;
                strcpy(hexbuf[stage], sha1_to_hex(ce->sha1));
-               sprintf(ownbuf[stage], "%o", ce->ce_mode);
+               xsnprintf(ownbuf[stage], sizeof(ownbuf[stage]), "%o", ce->ce_mode);