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Commit 7b6565db authored by Isaac J. Manjarres's avatar Isaac J. Manjarres
Browse files

lib: refcount: Cause kernel panic on refcount error detection 



Currently, when using the refcount API functions,
a warning is printed out once to let a user of
the refcount API know that an error case has been
detected. Then the refcount functions will
silently return, without modifying the reference count, which
could be mistaken for a successful modification. This can
allow for improper use of the object associated with that
refcount later. Trigger a kernel panic in case of refcount
error detection to prevent misuse of objects associated with
refcounts.

Change-Id: Ifb6a331d08a7d6c285225bc9667d2f4054db3561
Signed-off-by: default avatarIsaac J. Manjarres <isaacm@codeaurora.org>
parent 76f60b6d

arch/Kconfig

+9 −0
Original line number Diff line number Diff line
@@ -1027,4 +1027,13 @@ config REFCOUNT_FULL 
	  against various use-after-free conditions that can be used in

	  security flaw exploits.



config PANIC_ON_REFCOUNT_ERROR

	bool "Kernel panic on refcount error detection"

	depends on REFCOUNT_FULL

	help

	  If enabled, the kernel will panic when the refcount library

	  has detected any type of error (e.g. potential use-after-free

	  or potential memory-leaks) with an object associated with that

	  reference counter.



source "kernel/gcov/Kconfig"

lib/refcount.c

+26 −7
Original line number Diff line number Diff line
@@ -38,6 +38,18 @@ 
#include <linux/refcount.h>

#include <linux/bug.h>



#ifdef CONFIG_PANIC_ON_REFCOUNT_ERROR

#define REFCOUNT_WARN_ONCE(cond, msg) \

do { \

	if (cond) { \

		printk(msg); \

		BUG(); \

	} \

} while (0)

#else

#define REFCOUNT_WARN_ONCE(cond, msg) WARN_ONCE(cond, msg)

#endif /* CONFIG_PANIC_ON_REFCOUNT_ERROR */



#ifdef CONFIG_REFCOUNT_FULL



/**
@@ -75,7 +87,8 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r) 


	} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));



	WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");

	REFCOUNT_WARN_ONCE(new == UINT_MAX,

			   "refcount_t: saturated; leaking memory.\n");



	return true;

}
@@ -99,7 +112,8 @@ EXPORT_SYMBOL(refcount_add_not_zero); 
 */

void refcount_add(unsigned int i, refcount_t *r)

{

	WARN_ONCE(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");

	REFCOUNT_WARN_ONCE(!refcount_add_not_zero(i, r),

			   "refcount_t: addition on 0; use-after-free.\n");

}

EXPORT_SYMBOL(refcount_add);
@@ -130,7 +144,8 @@ bool refcount_inc_not_zero(refcount_t *r) 


	} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));



	WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");

	REFCOUNT_WARN_ONCE(new == UINT_MAX,

			   "refcount_t: saturated; leaking memory.\n");



	return true;

}
@@ -150,7 +165,8 @@ EXPORT_SYMBOL(refcount_inc_not_zero); 
 */

void refcount_inc(refcount_t *r)

{

	WARN_ONCE(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");

	REFCOUNT_WARN_ONCE(!refcount_inc_not_zero(r),

			   "refcount_t: increment on 0; use-after-free.\n");

}

EXPORT_SYMBOL(refcount_inc);
@@ -184,7 +200,8 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r) 


		new = val - i;

		if (new > val) {

			WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n");

			REFCOUNT_WARN_ONCE(new > val,

				"refcount_t: underflow; use-after-free.\n");

			return false;

		}
@@ -225,7 +242,8 @@ EXPORT_SYMBOL(refcount_dec_and_test); 
 */

void refcount_dec(refcount_t *r)

{

	WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");

	REFCOUNT_WARN_ONCE(refcount_dec_and_test(r),

			   "refcount_t: decrement hit 0; leaking memory.\n");

}

EXPORT_SYMBOL(refcount_dec);

#endif /* CONFIG_REFCOUNT_FULL */
@@ -278,7 +296,8 @@ bool refcount_dec_not_one(refcount_t *r) 


		new = val - 1;

		if (new > val) {

			WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n");

			REFCOUNT_WARN_ONCE(new > val,

				"refcount_t: underflow; use-after-free.\n");

			return true;

		}