| Message ID | 20170606174804.31124-5-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Jun 06, 2017 at 07:47:55PM +0200, Jason A. Donenfeld wrote: > -static inline void key_alloc_serial(struct key *key) > +static inline int key_alloc_serial(struct key *key) > @@ -170,7 +168,7 @@ static inline void key_alloc_serial(struct key *key) > rb_insert_color(&key->serial_node, &key_serial_tree); > > spin_unlock(&key_serial_lock); > - return; > + return 0; > > /* we found a key with the proposed serial number - walk the tree from > * that point looking for the next unused serial number */ > @@ -314,7 +312,9 @@ struct key *key_alloc(struct key_type *type, const char *desc, > > /* publish the key by giving it a serial number */ > atomic_inc(&user->nkeys); > - key_alloc_serial(key); > + ret = key_alloc_serial(key); > + if (ret < 0) > + goto security_error; > > error: > return key; I'm guessing you changed key_alloc_serial() to return an int back when you were thinking that you might use get_random_bytes_wait(), which could return -ERESTARTSYS. Now that you're not doing this, but using get_random_u32() instead, there's no point to change the function signature of key_alloc_serial() and add an error check in key_alloc() that will never fail, right? That's just adding a dead code path. Which the compiler can probably optimize away, but why make the code slightly harder to read than necessasry? - Ted
On Thu, Jun 8, 2017 at 2:31 AM, Theodore Ts'o <tytso@mit.edu> wrote: > I'm guessing you changed key_alloc_serial() to return an int back when > you were thinking that you might use get_random_bytes_wait(), which > could return -ERESTARTSYS. > > Now that you're not doing this, but using get_random_u32() instead, > there's no point to change the function signature of > key_alloc_serial() and add an error check in key_alloc() that will > never fail, right? That's just adding a dead code path. Which the > compiler can probably optimize away, but why make the code slightly > harder to read than necessasry? Good catch, and thanks for reading these so thoroughly that you caught the churn artifacts. Do you want me to clean this up and resubmit, or are you planning on adjusting it in the dev branch?
On Thu, Jun 8, 2017 at 2:50 AM, Jason A. Donenfeld <Jason@zx2c4.com> wrote: > On Thu, Jun 8, 2017 at 2:31 AM, Theodore Ts'o <tytso@mit.edu> wrote: >> I'm guessing you changed key_alloc_serial() to return an int back when >> you were thinking that you might use get_random_bytes_wait(), which >> could return -ERESTARTSYS. >> >> Now that you're not doing this, but using get_random_u32() instead, >> there's no point to change the function signature of >> key_alloc_serial() and add an error check in key_alloc() that will >> never fail, right? That's just adding a dead code path. Which the >> compiler can probably optimize away, but why make the code slightly >> harder to read than necessasry? > > Good catch, and thanks for reading these so thoroughly that you caught > the churn artifacts. Do you want me to clean this up and resubmit, or > are you planning on adjusting it in the dev branch? Fixed it up here if you just want to grab this instead: https://git.kernel.org/pub/scm/linux/kernel/git/zx2c4/linux.git/patch/?id=a0361e55bce30ace529ed8b28bd452e3ac0ee91f
diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c index 0010955d7876..d51a28fc5cd5 100644 --- a/security/keys/encrypted-keys/encrypted.c +++ b/security/keys/encrypted-keys/encrypted.c @@ -777,10 +777,12 @@ static int encrypted_init(struct encrypted_key_payload *epayload, __ekey_init(epayload, format, master_desc, datalen); if (!hex_encoded_iv) { - get_random_bytes(epayload->iv, ivsize); + ret = get_random_bytes_wait(epayload->iv, ivsize); + if (unlikely(ret)) + return ret; - get_random_bytes(epayload->decrypted_data, - epayload->decrypted_datalen); + ret = get_random_bytes_wait(epayload->decrypted_data, + epayload->decrypted_datalen); } else ret = encrypted_key_decrypt(epayload, format, hex_encoded_iv); return ret; diff --git a/security/keys/key.c b/security/keys/key.c index 455c04d80bbb..b72078e532f2 100644 --- a/security/keys/key.c +++ b/security/keys/key.c @@ -134,17 +134,15 @@ void key_user_put(struct key_user *user) * Allocate a serial number for a key. These are assigned randomly to avoid * security issues through covert channel problems. */ -static inline void key_alloc_serial(struct key *key) +static inline int key_alloc_serial(struct key *key) { struct rb_node *parent, **p; struct key *xkey; - /* propose a random serial number and look for a hole for it in the - * serial number tree */ + /* propose a non-negative random serial number and look for a hole for + * it in the serial number tree */ do { - get_random_bytes(&key->serial, sizeof(key->serial)); - - key->serial >>= 1; /* negative numbers are not permitted */ + key->serial = get_random_u32() >> 1; } while (key->serial < 3); spin_lock(&key_serial_lock); @@ -170,7 +168,7 @@ static inline void key_alloc_serial(struct key *key) rb_insert_color(&key->serial_node, &key_serial_tree); spin_unlock(&key_serial_lock); - return; + return 0; /* we found a key with the proposed serial number - walk the tree from * that point looking for the next unused serial number */ @@ -314,7 +312,9 @@ struct key *key_alloc(struct key_type *type, const char *desc, /* publish the key by giving it a serial number */ atomic_inc(&user->nkeys); - key_alloc_serial(key); + ret = key_alloc_serial(key); + if (ret < 0) + goto security_error; error: return key;
Otherwise, we might use bad random numbers which, particularly in the case of IV generation, could be quite bad. It makes sense to use the synchronous API here, because we're always in process context (as the code is littered with GFP_KERNEL and the like). However, we can't change to using a blocking function in key serial allocation, because this will block booting in some configurations, so here we use the more appropriate get_random_u32, which will use RDRAND if available. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Cc: David Howells <dhowells@redhat.com> Cc: Mimi Zohar <zohar@linux.vnet.ibm.com> Cc: David Safford <safford@us.ibm.com> --- security/keys/encrypted-keys/encrypted.c | 8 +++++--- security/keys/key.c | 16 ++++++++-------- 2 files changed, 13 insertions(+), 11 deletions(-)