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[SRU,Lunar,4/4] bpf: Avoid recomputing spi in process_dynptr_func

Message ID 20240126224453.46651-5-bethany.jamison@canonical.com
State New
Headers show
Series CVE-2023-39191 | expand

Commit Message

Bethany Jamison Jan. 26, 2024, 10:44 p.m. UTC 
From: Kumar Kartikeya Dwivedi <memxor@gmail.com>

Currently, process_dynptr_func first calls dynptr_get_spi and then
is_dynptr_reg_valid_init and is_dynptr_reg_valid_uninit have to call it
again to obtain the spi value. Instead of doing this twice, reuse the
already obtained value (which is by default 0, and is only set for
PTR_TO_STACK, and only used in that case in aforementioned functions).
The input value for these two functions will either be -ERANGE or >= 1,
and can either be permitted or rejected based on the respective check.

Suggested-by: Joanne Koong <joannelkoong@gmail.com>
Acked-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230121002241.2113993-8-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
(cherry picked from commit 1ee72bcbe48de6dcfa44d6eba0aec6e42d04cd4d)
CVE-2023-39191
Signed-off-by: Bethany Jamison <bethany.jamison@canonical.com>
---
 kernel/bpf/verifier.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a41f0af660d4..e6bd8af3c8b7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -955,14 +955,12 @@  static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,
 	return 0;
 }
 
-static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+				       int spi)
 {
-	int spi;
-
 	if (reg->type == CONST_PTR_TO_DYNPTR)
 		return false;
 
-	spi = dynptr_get_spi(env, reg);
 	/* For -ERANGE (i.e. spi not falling into allocated stack slots), we
 	 * will do check_mem_access to check and update stack bounds later, so
 	 * return true for that case.
@@ -980,16 +978,16 @@  static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_
 	return true;
 }
 
-static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+				     int spi)
 {
 	struct bpf_func_state *state = func(env, reg);
-	int spi, i;
+	int i;
 
 	/* This already represents first slot of initialized bpf_dynptr */
 	if (reg->type == CONST_PTR_TO_DYNPTR)
 		return true;
 
-	spi = dynptr_get_spi(env, reg);
 	if (spi < 0)
 		return false;
 	if (!state->stack[spi].spilled_ptr.dynptr.first_slot)
@@ -6207,6 +6205,7 @@  int process_dynptr_func(struct bpf_verifier_env *env, int regno,
 			enum bpf_arg_type arg_type, struct bpf_call_arg_meta *meta)
 {
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
+	int spi = 0;
 
 	/* MEM_UNINIT and MEM_RDONLY are exclusive, when applied to an
 	 * ARG_PTR_TO_DYNPTR (or ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_*):
@@ -6220,10 +6219,9 @@  int process_dynptr_func(struct bpf_verifier_env *env, int regno,
 	 * and its alignment for PTR_TO_STACK.
 	 */
 	if (reg->type == PTR_TO_STACK) {
-		int err = dynptr_get_spi(env, reg);
-
-		if (err < 0 && err != -ERANGE)
-			return err;
+		spi = dynptr_get_spi(env, reg);
+		if (spi < 0 && spi != -ERANGE)
+			return spi;
 	}
 
 	/*  MEM_UNINIT - Points to memory that is an appropriate candidate for
@@ -6242,7 +6240,7 @@  int process_dynptr_func(struct bpf_verifier_env *env, int regno,
 	 *		 to.
 	 */
 	if (arg_type & MEM_UNINIT) {
-		if (!is_dynptr_reg_valid_uninit(env, reg)) {
+		if (!is_dynptr_reg_valid_uninit(env, reg, spi)) {
 			verbose(env, "Dynptr has to be an uninitialized dynptr\n");
 			return -EINVAL;
 		}
@@ -6265,7 +6263,7 @@  int process_dynptr_func(struct bpf_verifier_env *env, int regno,
 			return -EINVAL;
 		}
 
-		if (!is_dynptr_reg_valid_init(env, reg)) {
+		if (!is_dynptr_reg_valid_init(env, reg, spi)) {
 			verbose(env,
 				"Expected an initialized dynptr as arg #%d\n",
 				regno);