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Subject: [PATCH] bpf: Reject BPF_MAP_TYPE_INSN_ARRAY in check_reg_const_str()
Author: kartikey406@gmail.com
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git master
BPF_MAP_TYPE_INSN_ARRAY maps store instruction pointers in their
ips array, not string data. The map_direct_value_addr callback for
this map type returns the address of the ips array, which is not
suitable for use as a constant string argument.
When a BPF program passes a pointer to an insn_array map value as
ARG_PTR_TO_CONST_STR (e.g., to bpf_snprintf), the verifier's
null-termination check in check_reg_const_str() operates on the
wrong memory region, and at runtime bpf_bprintf_prepare() can read
out of bounds searching for a null terminator.
Reject BPF_MAP_TYPE_INSN_ARRAY in check_reg_const_str() since this
map type is not designed to hold string data.
Reported-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
kernel/bpf/verifier.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f0ca69f888fa..3135643d5695 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9609,6 +9609,11 @@ static int check_reg_const_str(struct bpf_verifier_env *env,
if (reg->type != PTR_TO_MAP_VALUE)
return -EINVAL;
+ if (map->map_type == BPF_MAP_TYPE_INSN_ARRAY) {
+ verbose(env, "R%d points to insn_array map which cannot be used as const string\n", regno);
+ return -EACCES;
+ }
+
if (!bpf_map_is_rdonly(map)) {
verbose(env, "R%d does not point to a readonly map'\n", regno);
return -EACCES;
--
2.43.0