CVE-2014-7284 (published 2014-10-13T10:55Z)

The net_get_random_once implementation in net/core/utils.c in the Linux kernel 3.13.x and 3.14.x before 3.14.5 on certain Intel processors does not perform the intended slow-path operation to initialize random seeds, which makes it easier for remote attackers to spoof or disrupt IP communication by leveraging the predictability of TCP sequence numbers, TCP and UDP port numbers, and IP ID values.

Severity: MEDIUM
CVSS v2 base score: 6.4 (AV:N/AC:L/Au:N/C:N/I:P/A:P)

Weakness information:
cwe_id: CWE-200
cwe_name: Exposure of Sensitive Information to an Unauthorized Actor
description: The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
extended_description: 
	   There are many different kinds of mistakes that introduce information exposures. The severity of the error can range widely, depending on the context in which the product operates, the type of sensitive information that is revealed, and the benefits it may provide to an attacker.  Some kinds of sensitive information include:
       
         private, personal information, such as personal messages, financial data, health records, geographic location, or contact details
         system status and environment, such as the operating system and installed packages
		 business secrets and intellectual property
		 network status and configuration
		 the product's own code or internal state
         metadata, e.g. logging of connections or message headers
		 indirect information, such as a discrepancy between two internal operations that can be observed by an outsider
       
	    Information might be sensitive to different parties, each of which may have their own expectations for whether the information should be protected.  These parties include:
               
                  the product's own users
                  people or organizations whose information is created or used by the product, even if they are not direct product users
		  the product's administrators, including the admins of the system(s) and/or networks on which the product operates
                  the developer
               
	    Information exposures can occur in different ways:
               
                  the code explicitly inserts sensitive information into resources or messages that are intentionally made accessible to unauthorized actors, but should not contain the information - i.e., the information should have been "scrubbed" or "sanitized"
                  a different weakness or mistake indirectly inserts the sensitive information into resources, such as a web script error revealing the full system path of the program.
                  the code manages resources that intentionally contain sensitive information, but the resources are unintentionally made accessible to unauthorized actors. In this case, the information exposure is resultant - i.e., a different weakness enabled the access to the information in the first place.
               
	    It is common practice to describe any loss of confidentiality as an "information exposure," but this can lead to overuse of CWE-200 in CWE mapping. From the CWE perspective, loss of confidentiality is a technical impact that can arise from dozens of different weaknesses, such as insecure file permissions or out-of-bounds read.  CWE-200 and its lower-level descendants are intended to cover the mistakes that occur in behaviors that explicitly manage, store, transfer, or cleanse sensitive information.
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Hannes Frederic Sowa
author_date: 2014-05-11 22:59:30+02:00
msg: net: avoid dependency of net_get_random_once on nop patching

net_get_random_once depends on the static keys infrastructure to patch up
the branch to the slow path during boot. This was realized by abusing the
static keys api and defining a new initializer to not enable the call
site while still indicating that the branch point should get patched
up. This was needed to have the fast path considered likely by gcc.

The static key initialization during boot up normally walks through all
the registered keys and either patches in ideal nops or enables the jump
site but omitted that step on x86 if ideal nops where already placed at
static_key branch points. Thus net_get_random_once branches not always
became active.

This patch switches net_get_random_once to the ordinary static_key
api and thus places the kernel fast path in the - by gcc considered -
unlikely path.  Microbenchmarks on Intel and AMD x86-64 showed that
the unlikely path actually beats the likely path in terms of cycle cost
and that different nop patterns did not make much difference, thus this
switch should not be noticeable.

Fixes: a48e42920ff38b ("net: introduce new macro net_get_random_once")
Reported-by: Tuomas Räsänen <tuomasjjrasanen@tjjr.fi>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: net.h
change_type: ModificationType.MODIFY
diff: @@ -248,24 +248,17 @@ do {								\
 bool __net_get_random_once(void *buf, int nbytes, bool *done,
 			   struct static_key *done_key);
 
-#ifdef HAVE_JUMP_LABEL
-#define ___NET_RANDOM_STATIC_KEY_INIT ((struct static_key) \
-		{ .enabled = ATOMIC_INIT(0), .entries = (void *)1 })
-#else /* !HAVE_JUMP_LABEL */
-#define ___NET_RANDOM_STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
-#endif /* HAVE_JUMP_LABEL */
-
 #define net_get_random_once(buf, nbytes)				\
 	({								\
 		bool ___ret = false;					\
 		static bool ___done = false;				\
-		static struct static_key ___done_key =			\
-			___NET_RANDOM_STATIC_KEY_INIT;			\
-		if (!static_key_true(&___done_key))			\
+		static struct static_key ___once_key =			\
+			STATIC_KEY_INIT_TRUE;				\
+		if (static_key_true(&___once_key))			\
 			___ret = __net_get_random_once(buf,		\
 						       nbytes,		\
 						       &___done,	\
-						       &___done_key);	\
+						       &___once_key);	\
 		___ret;							\
 	})
 

programming_language: C
filename: utils.c
change_type: ModificationType.MODIFY
diff: @@ -348,8 +348,8 @@ static void __net_random_once_deferred(struct work_struct *w)
 {
 	struct __net_random_once_work *work =
 		container_of(w, struct __net_random_once_work, work);
-	if (!static_key_enabled(work->key))
-		static_key_slow_inc(work->key);
+	BUG_ON(!static_key_enabled(work->key));
+	static_key_slow_dec(work->key);
 	kfree(work);
 }
 
@@ -367,7 +367,7 @@ static void __net_random_once_disable_jump(struct static_key *key)
 }
 
 bool __net_get_random_once(void *buf, int nbytes, bool *done,
-			   struct static_key *done_key)
+			   struct static_key *once_key)
 {
 	static DEFINE_SPINLOCK(lock);
 	unsigned long flags;
@@ -382,7 +382,7 @@ bool __net_get_random_once(void *buf, int nbytes, bool *done,
 	*done = true;
 	spin_unlock_irqrestore(&lock, flags);
 
-	__net_random_once_disable_jump(done_key);
+	__net_random_once_disable_jump(once_key);
 
 	return true;
 }

programming_language: C