This is a note to let you know that I've just added the patch titled
bpf, lsm: Add check for BPF LSM return value
to the 6.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-lsm-add-check-for-bpf-lsm-return-value.patch
and it can be found in the queue-6.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 0944b4a1a53f6def7df74668f283d4294de4fa57
Author: Xu Kuohai <xukuohai@xxxxxxxxxx>
Date: Fri Jul 19 19:00:52 2024 +0800
bpf, lsm: Add check for BPF LSM return value
[ Upstream commit 5d99e198be279045e6ecefe220f5c52f8ce9bfd5 ]
A bpf prog returning a positive number attached to file_alloc_security
hook makes kernel panic.
This happens because file system can not filter out the positive number
returned by the LSM prog using IS_ERR, and misinterprets this positive
number as a file pointer.
Given that hook file_alloc_security never returned positive number
before the introduction of BPF LSM, and other BPF LSM hooks may
encounter similar issues, this patch adds LSM return value check
in verifier, to ensure no unexpected value is returned.
Fixes: 520b7aa00d8c ("bpf: lsm: Initialize the BPF LSM hooks")
Reported-by: Xin Liu <liuxin350@xxxxxxxxxx>
Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Link: https://lore.kernel.org/r/20240719110059.797546-3-xukuohai@xxxxxxxxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5e694a308081a..42b998518038a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -927,6 +927,7 @@ struct bpf_insn_access_aux {
};
};
struct bpf_verifier_log *log; /* for verbose logs */
+ bool is_retval; /* is accessing function return value ? */
};
static inline void
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
index 1de7ece5d36d4..aefcd65642512 100644
--- a/include/linux/bpf_lsm.h
+++ b/include/linux/bpf_lsm.h
@@ -9,6 +9,7 @@
#include <linux/sched.h>
#include <linux/bpf.h>
+#include <linux/bpf_verifier.h>
#include <linux/lsm_hooks.h>
#ifdef CONFIG_BPF_LSM
@@ -45,6 +46,8 @@ void bpf_inode_storage_free(struct inode *inode);
void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, bpf_func_t *bpf_func);
+int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
+ struct bpf_retval_range *range);
#else /* !CONFIG_BPF_LSM */
static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id)
@@ -78,6 +81,11 @@ static inline void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
{
}
+static inline int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
+ struct bpf_retval_range *range)
+{
+ return -EOPNOTSUPP;
+}
#endif /* CONFIG_BPF_LSM */
#endif /* _LINUX_BPF_LSM_H */
diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 68240c3c6e7de..7f8a66a62661b 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -11,7 +11,6 @@
#include <linux/lsm_hooks.h>
#include <linux/bpf_lsm.h>
#include <linux/kallsyms.h>
-#include <linux/bpf_verifier.h>
#include <net/bpf_sk_storage.h>
#include <linux/bpf_local_storage.h>
#include <linux/btf_ids.h>
@@ -389,3 +388,36 @@ const struct bpf_verifier_ops lsm_verifier_ops = {
.get_func_proto = bpf_lsm_func_proto,
.is_valid_access = btf_ctx_access,
};
+
+/* hooks return 0 or 1 */
+BTF_SET_START(bool_lsm_hooks)
+#ifdef CONFIG_SECURITY_NETWORK_XFRM
+BTF_ID(func, bpf_lsm_xfrm_state_pol_flow_match)
+#endif
+#ifdef CONFIG_AUDIT
+BTF_ID(func, bpf_lsm_audit_rule_known)
+#endif
+BTF_ID(func, bpf_lsm_inode_xattr_skipcap)
+BTF_SET_END(bool_lsm_hooks)
+
+int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
+ struct bpf_retval_range *retval_range)
+{
+ /* no return value range for void hooks */
+ if (!prog->aux->attach_func_proto->type)
+ return -EINVAL;
+
+ if (btf_id_set_contains(&bool_lsm_hooks, prog->aux->attach_btf_id)) {
+ retval_range->minval = 0;
+ retval_range->maxval = 1;
+ } else {
+ /* All other available LSM hooks, except task_prctl, return 0
+ * on success and negative error code on failure.
+ * To keep things simple, we only allow bpf progs to return 0
+ * or negative errno for task_prctl too.
+ */
+ retval_range->minval = -MAX_ERRNO;
+ retval_range->maxval = 0;
+ }
+ return 0;
+}
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 2f157ffbc67ce..49aba8e507996 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6250,8 +6250,11 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
if (arg == nr_args) {
switch (prog->expected_attach_type) {
- case BPF_LSM_CGROUP:
case BPF_LSM_MAC:
+ /* mark we are accessing the return value */
+ info->is_retval = true;
+ fallthrough;
+ case BPF_LSM_CGROUP:
case BPF_TRACE_FEXIT:
/* When LSM programs are attached to void LSM hooks
* they use FEXIT trampolines and when attached to
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 73f55f4b945ee..b95f7f5bd5a49 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2334,6 +2334,25 @@ static void mark_reg_unknown(struct bpf_verifier_env *env,
__mark_reg_unknown(env, regs + regno);
}
+static int __mark_reg_s32_range(struct bpf_verifier_env *env,
+ struct bpf_reg_state *regs,
+ u32 regno,
+ s32 s32_min,
+ s32 s32_max)
+{
+ struct bpf_reg_state *reg = regs + regno;
+
+ reg->s32_min_value = max_t(s32, reg->s32_min_value, s32_min);
+ reg->s32_max_value = min_t(s32, reg->s32_max_value, s32_max);
+
+ reg->smin_value = max_t(s64, reg->smin_value, s32_min);
+ reg->smax_value = min_t(s64, reg->smax_value, s32_max);
+
+ reg_bounds_sync(reg);
+
+ return reg_bounds_sanity_check(env, reg, "s32_range");
+}
+
static void __mark_reg_not_init(const struct bpf_verifier_env *env,
struct bpf_reg_state *reg)
{
@@ -5575,11 +5594,12 @@ static int check_packet_access(struct bpf_verifier_env *env, u32 regno, int off,
/* check access to 'struct bpf_context' fields. Supports fixed offsets only */
static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off, int size,
enum bpf_access_type t, enum bpf_reg_type *reg_type,
- struct btf **btf, u32 *btf_id)
+ struct btf **btf, u32 *btf_id, bool *is_retval)
{
struct bpf_insn_access_aux info = {
.reg_type = *reg_type,
.log = &env->log,
+ .is_retval = false,
};
if (env->ops->is_valid_access &&
@@ -5592,6 +5612,7 @@ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off,
* type of narrower access.
*/
*reg_type = info.reg_type;
+ *is_retval = info.is_retval;
if (base_type(*reg_type) == PTR_TO_BTF_ID) {
*btf = info.btf;
@@ -6760,6 +6781,17 @@ static int check_stack_access_within_bounds(
return grow_stack_state(env, state, -min_off /* size */);
}
+static bool get_func_retval_range(struct bpf_prog *prog,
+ struct bpf_retval_range *range)
+{
+ if (prog->type == BPF_PROG_TYPE_LSM &&
+ prog->expected_attach_type == BPF_LSM_MAC &&
+ !bpf_lsm_get_retval_range(prog, range)) {
+ return true;
+ }
+ return false;
+}
+
/* check whether memory at (regno + off) is accessible for t = (read | write)
* if t==write, value_regno is a register which value is stored into memory
* if t==read, value_regno is a register which will receive the value from memory
@@ -6864,6 +6896,8 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
if (!err && value_regno >= 0 && (t == BPF_READ || rdonly_mem))
mark_reg_unknown(env, regs, value_regno);
} else if (reg->type == PTR_TO_CTX) {
+ bool is_retval = false;
+ struct bpf_retval_range range;
enum bpf_reg_type reg_type = SCALAR_VALUE;
struct btf *btf = NULL;
u32 btf_id = 0;
@@ -6879,7 +6913,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
return err;
err = check_ctx_access(env, insn_idx, off, size, t, ®_type, &btf,
- &btf_id);
+ &btf_id, &is_retval);
if (err)
verbose_linfo(env, insn_idx, "; ");
if (!err && t == BPF_READ && value_regno >= 0) {
@@ -6888,7 +6922,14 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
* case, we know the offset is zero.
*/
if (reg_type == SCALAR_VALUE) {
- mark_reg_unknown(env, regs, value_regno);
+ if (is_retval && get_func_retval_range(env->prog, &range)) {
+ err = __mark_reg_s32_range(env, regs, value_regno,
+ range.minval, range.maxval);
+ if (err)
+ return err;
+ } else {
+ mark_reg_unknown(env, regs, value_regno);
+ }
} else {
mark_reg_known_zero(env, regs,
value_regno);
@@ -15677,12 +15718,13 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
case BPF_PROG_TYPE_LSM:
if (env->prog->expected_attach_type != BPF_LSM_CGROUP) {
- /* Regular BPF_PROG_TYPE_LSM programs can return
- * any value.
- */
- return 0;
- }
- if (!env->prog->aux->attach_func_proto->type) {
+ /* no range found, any return value is allowed */
+ if (!get_func_retval_range(env->prog, &range))
+ return 0;
+ /* no restricted range, any return value is allowed */
+ if (range.minval == S32_MIN && range.maxval == S32_MAX)
+ return 0;
+ } else if (!env->prog->aux->attach_func_proto->type) {
/* Make sure programs that attach to void
* hooks don't try to modify return value.
*/
