Re: [PATCH 01/11] mingw: avoid accessing uninitialized memory in `is_executable()`

René Scharfe [off-list ref] writes:

Am 16.06.22 um 01:35 schrieb Johannes Schindelin via GitGitGadget:

quoted

From: Johannes Schindelin <redacted>

On Windows, we open files we suspect might be scripts, read the first
two bytes, and see whether they indicate a hash-bang line. We do not
initialize the byte _after_ those two bytes, therefore `strcmp()` is
inappropriate here.

Hmm, but buf _is_ initialized fully?  Line 149:

        char buf[3] = { 0 };

Ahh, yeah, that changes the landscape quite a bit.

We explicitly ask to read 2 bytes and look at the buf[] when read
says it read 2 bytes, so this is another false positive X-<.

quoted

diff --git a/run-command.c b/run-command.c
index 14f17830f51..2ba38850b4d 100644
--- a/run-command.c
+++ b/run-command.c

@@ -154,7 +154,7 @@ int is_executable(const char *name)
 		n = read(fd, buf, 2);
 		if (n == 2)
 			/* look for a she-bang */
-			if (!strcmp(buf, "#!"))
+			if (!memcmp(buf, "#!", 2))
 				st.st_mode |= S_IXUSR;
 		close(fd);
 	}

We can update the variable to

	char buf[2];

to match the updated code, I guess.  The fewer bytes we use on
stack, the better ;-).