linux-kernel - [PATCH 3.19 168/177] ebpf: verifier: check that call reg with ARG

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Message-Id: <20150502190127.626856180@linuxfoundation.org>
Date:	Sat,  2 May 2015 21:03:10 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.19 168/177] ebpf: verifier: check that call reg with ARG_ANYTHING is initialized

3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <daniel@...earbox.net>

commit 80f1d68ccba70b1060c9c7360ca83da430f66bed upstream.

I noticed that a helper function with argument type ARG_ANYTHING does
not need to have an initialized value (register).

This can worst case lead to unintented stack memory leakage in future
helper functions if they are not carefully designed, or unintended
application behaviour in case the application developer was not careful
enough to match a correct helper function signature in the API.

The underlying issue is that ARG_ANYTHING should actually be split
into two different semantics:

  1) ARG_DONTCARE for function arguments that the helper function
     does not care about (in other words: the default for unused
     function arguments), and

  2) ARG_ANYTHING that is an argument actually being used by a
     helper function and *guaranteed* to be an initialized register.

The current risk is low: ARG_ANYTHING is only used for the 'flags'
argument (r4) in bpf_map_update_elem() that internally does strict
checking.

Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)")
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Alexei Starovoitov <ast@...mgrid.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/linux/bpf.h   |    4 +++-
 kernel/bpf/verifier.c |    5 ++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -48,7 +48,7 @@ struct bpf_map *bpf_map_get(struct fd f)
 
 /* function argument constraints */
 enum bpf_arg_type {
-	ARG_ANYTHING = 0,	/* any argument is ok */
+	ARG_DONTCARE = 0,	/* unused argument in helper function */
 
 	/* the following constraints used to prototype
 	 * bpf_map_lookup/update/delete_elem() functions
@@ -62,6 +62,8 @@ enum bpf_arg_type {
 	 */
 	ARG_PTR_TO_STACK,	/* any pointer to eBPF program stack */
 	ARG_CONST_STACK_SIZE,	/* number of bytes accessed from stack */
+
+	ARG_ANYTHING,		/* any (initialized) argument is ok */
 };
 
 /* type of values returned from helper functions */
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -755,7 +755,7 @@ static int check_func_arg(struct verifie
 	enum bpf_reg_type expected_type;
 	int err = 0;
 
-	if (arg_type == ARG_ANYTHING)
+	if (arg_type == ARG_DONTCARE)
 		return 0;
 
 	if (reg->type == NOT_INIT) {
@@ -763,6 +763,9 @@ static int check_func_arg(struct verifie
 		return -EACCES;
 	}
 
+	if (arg_type == ARG_ANYTHING)
+		return 0;
+
 	if (arg_type == ARG_PTR_TO_STACK || arg_type == ARG_PTR_TO_MAP_KEY ||
 	    arg_type == ARG_PTR_TO_MAP_VALUE) {
 		expected_type = PTR_TO_STACK;


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