From aa9d4437893f7e015ce5b6d6c443a9ba92c8a2e7 Mon Sep 17 00:00:00 2001 From: David Howells Date: Mon, 1 Dec 2014 22:52:45 +0000 Subject: KEYS: Fix the size of the key description passed to/from userspace When a key description argument is imported into the kernel from userspace, as happens in add_key(), request_key(), KEYCTL_JOIN_SESSION_KEYRING, KEYCTL_SEARCH, the description is copied into a buffer up to PAGE_SIZE in size. PAGE_SIZE, however, is a variable quantity, depending on the arch. Fix this at 4096 instead (ie. 4095 plus a NUL termination) and define a constant (KEY_MAX_DESC_SIZE) to this end. When reading the description back with KEYCTL_DESCRIBE, a PAGE_SIZE internal buffer is allocated into which the information and description will be rendered. This means that the description will get truncated if an extremely long description it has to be crammed into the buffer with the stringified information. There is no particular need to copy the description into the buffer, so just copy it directly to userspace in a separate operation. Reported-by: Christian Kastner Signed-off-by: David Howells Tested-by: Christian Kastner --- security/keys/keyctl.c | 56 +++++++++++++++++++++++--------------------------- 1 file changed, 26 insertions(+), 30 deletions(-) diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c index eff88a5f5d40..4743d71e4aa6 100644 --- a/security/keys/keyctl.c +++ b/security/keys/keyctl.c @@ -26,6 +26,8 @@ #include #include "internal.h" +#define KEY_MAX_DESC_SIZE 4096 + static int key_get_type_from_user(char *type, const char __user *_type, unsigned len) @@ -78,7 +80,7 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type, description = NULL; if (_description) { - description = strndup_user(_description, PAGE_SIZE); + description = strndup_user(_description, KEY_MAX_DESC_SIZE); if (IS_ERR(description)) { ret = PTR_ERR(description); goto error; @@ -177,7 +179,7 @@ SYSCALL_DEFINE4(request_key, const char __user *, _type, goto error; /* pull the description into kernel space */ - description = strndup_user(_description, PAGE_SIZE); + description = strndup_user(_description, KEY_MAX_DESC_SIZE); if (IS_ERR(description)) { ret = PTR_ERR(description); goto error; @@ -287,7 +289,7 @@ long keyctl_join_session_keyring(const char __user *_name) /* fetch the name from userspace */ name = NULL; if (_name) { - name = strndup_user(_name, PAGE_SIZE); + name = strndup_user(_name, KEY_MAX_DESC_SIZE); if (IS_ERR(name)) { ret = PTR_ERR(name); goto error; @@ -562,8 +564,9 @@ long keyctl_describe_key(key_serial_t keyid, { struct key *key, *instkey; key_ref_t key_ref; - char *tmpbuf; + char *infobuf; long ret; + int desclen, infolen; key_ref = lookup_user_key(keyid, KEY_LOOKUP_PARTIAL, KEY_NEED_VIEW); if (IS_ERR(key_ref)) { @@ -586,38 +589,31 @@ long keyctl_describe_key(key_serial_t keyid, } okay: - /* calculate how much description we're going to return */ - ret = -ENOMEM; - tmpbuf = kmalloc(PAGE_SIZE, GFP_KERNEL); - if (!tmpbuf) - goto error2; - key = key_ref_to_ptr(key_ref); + desclen = strlen(key->description); - ret = snprintf(tmpbuf, PAGE_SIZE - 1, - "%s;%d;%d;%08x;%s", - key->type->name, - from_kuid_munged(current_user_ns(), key->uid), - from_kgid_munged(current_user_ns(), key->gid), - key->perm, - key->description ?: ""); - - /* include a NUL char at the end of the data */ - if (ret > PAGE_SIZE - 1) - ret = PAGE_SIZE - 1; - tmpbuf[ret] = 0; - ret++; + /* calculate how much information we're going to return */ + ret = -ENOMEM; + infobuf = kasprintf(GFP_KERNEL, + "%s;%d;%d;%08x;", + key->type->name, + from_kuid_munged(current_user_ns(), key->uid), + from_kgid_munged(current_user_ns(), key->gid), + key->perm); + if (!infobuf) + goto error2; + infolen = strlen(infobuf); + ret = infolen + desclen + 1; /* consider returning the data */ - if (buffer && buflen > 0) { - if (buflen > ret) - buflen = ret; - - if (copy_to_user(buffer, tmpbuf, buflen) != 0) + if (buffer && buflen >= ret) { + if (copy_to_user(buffer, infobuf, infolen) != 0 || + copy_to_user(buffer + infolen, key->description, + desclen + 1) != 0) ret = -EFAULT; } - kfree(tmpbuf); + kfree(infobuf); error2: key_ref_put(key_ref); error: @@ -649,7 +645,7 @@ long keyctl_keyring_search(key_serial_t ringid, if (ret < 0) goto error; - description = strndup_user(_description, PAGE_SIZE); + description = strndup_user(_description, KEY_MAX_DESC_SIZE); if (IS_ERR(description)) { ret = PTR_ERR(description); goto error; -- cgit v1.2.3 From 054f6180d8b5602b431b5924976c956e760488b1 Mon Sep 17 00:00:00 2001 From: David Howells Date: Mon, 1 Dec 2014 22:52:50 +0000 Subject: KEYS: Simplify KEYRING_SEARCH_{NO,DO}_STATE_CHECK flags Simplify KEYRING_SEARCH_{NO,DO}_STATE_CHECK flags to be two variations of the same flag. They are effectively mutually exclusive and one or the other should be provided, but not both. Keyring cycle detection and key possession determination are the only things that set NO_STATE_CHECK, except that neither flag really does anything there because neither purpose makes use of the keyring_search_iterator() function, but rather provides their own. For cycle detection we definitely want to check inside of expired keyrings, just so that we don't create a cycle we can't get rid of. Revoked keyrings are cleared at revocation time and can't then be reused, so shouldn't be a problem either way. For possession determination, we *might* want to validate each keyring before searching it: do you possess a key that's hidden behind an expired or just plain inaccessible keyring? Currently, the answer is yes. Note that you cannot, however, possess a key behind a revoked keyring because they are cleared on revocation. keyring_search() sets DO_STATE_CHECK, which is correct. request_key_and_link() currently doesn't specify whether to check the key state or not - but it should set DO_STATE_CHECK. key_get_instantiation_authkey() also currently doesn't specify whether to check the key state or not - but it probably should also set DO_STATE_CHECK. Signed-off-by: David Howells Tested-by: Chuck Lever --- security/keys/keyring.c | 7 ++++--- security/keys/request_key.c | 1 + security/keys/request_key_auth.c | 1 + 3 files changed, 6 insertions(+), 3 deletions(-) diff --git a/security/keys/keyring.c b/security/keys/keyring.c index 8177010174f7..238aa172f25b 100644 --- a/security/keys/keyring.c +++ b/security/keys/keyring.c @@ -628,6 +628,10 @@ static bool search_nested_keyrings(struct key *keyring, ctx->index_key.type->name, ctx->index_key.description); +#define STATE_CHECKS (KEYRING_SEARCH_NO_STATE_CHECK | KEYRING_SEARCH_DO_STATE_CHECK) + BUG_ON((ctx->flags & STATE_CHECKS) == 0 || + (ctx->flags & STATE_CHECKS) == STATE_CHECKS); + if (ctx->index_key.description) ctx->index_key.desc_len = strlen(ctx->index_key.description); @@ -637,7 +641,6 @@ static bool search_nested_keyrings(struct key *keyring, if (ctx->match_data.lookup_type == KEYRING_SEARCH_LOOKUP_ITERATE || keyring_compare_object(keyring, &ctx->index_key)) { ctx->skipped_ret = 2; - ctx->flags |= KEYRING_SEARCH_DO_STATE_CHECK; switch (ctx->iterator(keyring_key_to_ptr(keyring), ctx)) { case 1: goto found; @@ -649,8 +652,6 @@ static bool search_nested_keyrings(struct key *keyring, } ctx->skipped_ret = 0; - if (ctx->flags & KEYRING_SEARCH_NO_STATE_CHECK) - ctx->flags &= ~KEYRING_SEARCH_DO_STATE_CHECK; /* Start processing a new keyring */ descend_to_keyring: diff --git a/security/keys/request_key.c b/security/keys/request_key.c index bb4337c7ae1b..0bb23f98e4ca 100644 --- a/security/keys/request_key.c +++ b/security/keys/request_key.c @@ -516,6 +516,7 @@ struct key *request_key_and_link(struct key_type *type, .match_data.cmp = key_default_cmp, .match_data.raw_data = description, .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT, + .flags = KEYRING_SEARCH_DO_STATE_CHECK, }; struct key *key; key_ref_t key_ref; diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c index 6639e2cb8853..5d672f7580dd 100644 --- a/security/keys/request_key_auth.c +++ b/security/keys/request_key_auth.c @@ -249,6 +249,7 @@ struct key *key_get_instantiation_authkey(key_serial_t target_id) .match_data.cmp = key_default_cmp, .match_data.raw_data = description, .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT, + .flags = KEYRING_SEARCH_DO_STATE_CHECK, }; struct key *authkey; key_ref_t authkey_ref; -- cgit v1.2.3 From 0b0a84154eff56913e91df29de5c3a03a0029e38 Mon Sep 17 00:00:00 2001 From: David Howells Date: Mon, 1 Dec 2014 22:52:53 +0000 Subject: KEYS: request_key() should reget expired keys rather than give EKEYEXPIRED Since the keyring facility can be viewed as a cache (at least in some applications), the local expiration time on the key should probably be viewed as a 'needs updating after this time' property rather than an absolute 'anyone now wanting to use this object is out of luck' property. Since request_key() is the main interface for the usage of keys, this should update or replace an expired key rather than issuing EKEYEXPIRED if the local expiration has been reached (ie. it should refresh the cache). For absolute conditions where refreshing the cache probably doesn't help, the key can be negatively instantiated using KEYCTL_REJECT_KEY with EKEYEXPIRED given as the error to issue. This will still cause request_key() to return EKEYEXPIRED as that was explicitly set. In the future, if the key type has an update op available, we might want to upcall with the expired key and allow the upcall to update it. We would pass a different operation name (the first column in /etc/request-key.conf) to the request-key program. request_key() returning EKEYEXPIRED is causing an NFS problem which Chuck Lever describes thusly: After about 10 minutes, my NFSv4 functional tests fail because the ownership of the test files goes to "-2". Looking at /proc/keys shows that the id_resolv keys that map to my test user ID have expired. The ownership problem persists until the expired keys are purged from the keyring, and fresh keys are obtained. I bisected the problem to 3.13 commit b2a4df200d57 ("KEYS: Expand the capacity of a keyring"). This commit inadvertantly changes the API contract of the internal function keyring_search_aux(). The root cause appears to be that b2a4df200d57 made "no state check" the default behavior. "No state check" means the keyring search iterator function skips checking the key's expiry timeout, and returns expired keys. request_key_and_link() depends on getting an -EAGAIN result code to know when to perform an upcall to refresh an expired key. This patch can be tested directly by: keyctl request2 user debug:fred a @s keyctl timeout %user:debug:fred 3 sleep 4 keyctl request2 user debug:fred a @s Without the patch, the last command gives error EKEYEXPIRED, but with the command it gives a new key. Reported-by: Carl Hetherington Reported-by: Chuck Lever Signed-off-by: David Howells Tested-by: Chuck Lever --- security/keys/internal.h | 1 + security/keys/keyring.c | 3 ++- security/keys/request_key.c | 3 ++- 3 files changed, 5 insertions(+), 2 deletions(-) diff --git a/security/keys/internal.h b/security/keys/internal.h index b8960c4959a5..200e37867336 100644 --- a/security/keys/internal.h +++ b/security/keys/internal.h @@ -117,6 +117,7 @@ struct keyring_search_context { #define KEYRING_SEARCH_NO_UPDATE_TIME 0x0004 /* Don't update times */ #define KEYRING_SEARCH_NO_CHECK_PERM 0x0008 /* Don't check permissions */ #define KEYRING_SEARCH_DETECT_TOO_DEEP 0x0010 /* Give an error on excessive depth */ +#define KEYRING_SEARCH_SKIP_EXPIRED 0x0020 /* Ignore expired keys (intention to replace) */ int (*iterator)(const void *object, void *iterator_data); diff --git a/security/keys/keyring.c b/security/keys/keyring.c index 238aa172f25b..e72548b5897e 100644 --- a/security/keys/keyring.c +++ b/security/keys/keyring.c @@ -546,7 +546,8 @@ static int keyring_search_iterator(const void *object, void *iterator_data) } if (key->expiry && ctx->now.tv_sec >= key->expiry) { - ctx->result = ERR_PTR(-EKEYEXPIRED); + if (!(ctx->flags & KEYRING_SEARCH_SKIP_EXPIRED)) + ctx->result = ERR_PTR(-EKEYEXPIRED); kleave(" = %d [expire]", ctx->skipped_ret); goto skipped; } diff --git a/security/keys/request_key.c b/security/keys/request_key.c index 0bb23f98e4ca..0c7aea4dea54 100644 --- a/security/keys/request_key.c +++ b/security/keys/request_key.c @@ -516,7 +516,8 @@ struct key *request_key_and_link(struct key_type *type, .match_data.cmp = key_default_cmp, .match_data.raw_data = description, .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT, - .flags = KEYRING_SEARCH_DO_STATE_CHECK, + .flags = (KEYRING_SEARCH_DO_STATE_CHECK | + KEYRING_SEARCH_SKIP_EXPIRED), }; struct key *key; key_ref_t key_ref; -- cgit v1.2.3