fusermount: Reject invalid negative mount_max in fuse.conf

mount_max is parsed with %i (signed) from /etc/fuse.conf. The value
-1 is the documented sentinel for "no limit", but any other negative
value (e.g., -2 from a typo) passes the mount_max != -1 guard and
makes the mount_count >= mount_max comparison always true, blocking
all non-root FUSE mounts.

Reject values below -1 with a warning rather than silently accepting
them.

Signed-off-by: Abhinav Agarwal <abhinavagarwal1996@gmail.com>

util/fuser_conf.c

diff --git a/util/fuser_conf.c b/util/fuser_conf.c
index 8203b14..31b78fc 100644
--- a/util/fuser_conf.c
+++ b/util/fuser_conf.c
@@ -192,8 +192,14 @@
 
 	if (strcmp(line, "user_allow_other") == 0)
 		user_allow_other = 1;
-	else if (sscanf(line, "mount_max = %i", &tmp) == 1)
-		mount_max = tmp;
+	else if (sscanf(line, "mount_max = %i", &tmp) == 1) {
+		if (tmp < -1)
+			fprintf(stderr,
+				"%s: invalid mount_max = %i in %s at line %i\n",
+				progname, tmp, FUSE_CONF, linenum);
+		else
+			mount_max = tmp;
+	}
 	else if (line[0])
 		fprintf(stderr,
 			"%s: unknown parameter in %s at line %i: '%s'\n",