[PATCH v2 5/6] KEYS: load key flags and expiry time atomically in proc_keys_show()

Eric Biggers
2017-09-26T20:16:17Z

In proc_keys_show(), the key semaphore is not held, so the key ->flags
and ->expiry can be changed concurrently. We therefore should read them
atomically just once. Otherwise /proc/keys may show an inconsistent
state, such a key that is negative ('N') but not instantiated ('I').

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
security/keys/proc.c | 28 ++++++++++++++++------------
1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/security/keys/proc.c b/security/keys/proc.c
index de834309d100..a038069ac46a 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -179,7 +179,9 @@ static int proc_keys_show(struct seq_file *m, void *v)
struct rb_node *_p = v;
struct key *key = rb_entry(_p, struct key, serial_node);
struct timespec now;
+ time_t expiry;
unsigned long timo;
+ unsigned long flags;
key_ref_t key_ref, skey_ref;
char xbuf[16];
int rc;
@@ -217,12 +219,13 @@ static int proc_keys_show(struct seq_file *m, void *v)
rcu_read_lock();

/* come up with a suitable timeout value */
- if (key->expiry == 0) {
+ expiry = READ_ONCE(key->expiry);
+ if (expiry == 0) {
memcpy(xbuf, "perm", 5);
- } else if (now.tv_sec >= key->expiry) {
+ } else if (now.tv_sec >= expiry) {
memcpy(xbuf, "expd", 5);
} else {
- timo = key->expiry - now.tv_sec;
+ timo = expiry - now.tv_sec;

if (timo < 60)
sprintf(xbuf, "%lus", timo);
@@ -236,18 +239,19 @@ static int proc_keys_show(struct seq_file *m, void *v)
sprintf(xbuf, "%luw", timo / (60*60*24*7));
}

-#define showflag(KEY, LETTER, FLAG) \
- (test_bit(FLAG, &(KEY)->flags) ? LETTER : '-')
+#define showflag(FLAGS, LETTER, FLAG) \
+ ((FLAGS & (1 << FLAG)) ? LETTER : '-')

+ flags = READ_ONCE(key->flags);
seq_printf(m, "%08x %c%c%c%c%c%c%c %5d %4s %08x %5d %5d %-9.9s ",
key->serial,
- showflag(key, 'I', KEY_FLAG_INSTANTIATED),
- showflag(key, 'R', KEY_FLAG_REVOKED),
- showflag(key, 'D', KEY_FLAG_DEAD),
- showflag(key, 'Q', KEY_FLAG_IN_QUOTA),
- showflag(key, 'U', KEY_FLAG_USER_CONSTRUCT),
- showflag(key, 'N', KEY_FLAG_NEGATIVE),
- showflag(key, 'i', KEY_FLAG_INVALIDATED),
+ showflag(flags, 'I', KEY_FLAG_INSTANTIATED),
+ showflag(flags, 'R', KEY_FLAG_REVOKED),
+ showflag(flags, 'D', KEY_FLAG_DEAD),
+ showflag(flags, 'Q', KEY_FLAG_IN_QUOTA),
+ showflag(flags, 'U', KEY_FLAG_USER_CONSTRUCT),
+ showflag(flags, 'N', KEY_FLAG_NEGATIVE),
+ showflag(flags, 'i', KEY_FLAG_INVALIDATED),
refcount_read(&key->usage),
xbuf,
key->perm,
--
2.14.1.992.g2c7b836f3a-goog