fusermount: refuse unknown options

Blacklists are notoriously fragile; especially if the kernel wishes to add
some security-critical mount option at a later date, all existing systems
with older versions of fusermount installed will suddenly have a security
problem.
Additionally, if the kernel's option parsing became a tiny bit laxer, the
blacklist could probably be bypassed.

Whitelist known-harmless flags instead, even if it's slightly more
inconvenient.

1 files changed, 7 insertions, 1 deletions

diff --git a/util/fusermount.c b/util/fusermount.c
index 4e0f51a..2792407 100644
--- a/util/fusermount.c
+++ b/util/fusermount.c
@@ -819,10 +819,16 @@ static int do_mount(const char *mnt, char **typep, mode_t rootmode,
 						flags |= flag;
 					else
 						flags  &= ~flag;
-				} else {
+				} else if (opt_eq(s, len, "default_permissions") ||
+					   opt_eq(s, len, "allow_other") ||
+					   begins_with(s, "max_read=") ||
+					   begins_with(s, "blksize=")) {
 					memcpy(d, s, len);
 					d += len;
 					*d++ = ',';
+				} else {
+					fprintf(stderr, "%s: unknown option '%.*s'\n", progname, len, s);
+					exit(1);
 				}
 			}
 		}