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| author | Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2022-03-19 13:38:24 +0530 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-04-06 10:32:12 -0700 |
| commit | 97e6d7dab1ca4648821c790a2b7913d6d5d549db (patch) | |
| tree | 81e00e777021fffcc5735d2af73b4a30d859f1f1 /kernel | |
| parent | be77354a3d7ebd4897ee18eca26dca6df9224c76 (diff) | |
| download | linux-97e6d7dab1ca4648821c790a2b7913d6d5d549db.tar.bz2 | |
bpf: Check PTR_TO_MEM | MEM_RDONLY in check_helper_mem_access
The commit being fixed was aiming to disallow users from incorrectly
obtaining writable pointer to memory that is only meant to be read. This
is enforced now using a MEM_RDONLY flag.
For instance, in case of global percpu variables, when the BTF type is
not struct (e.g. bpf_prog_active), the verifier marks register type as
PTR_TO_MEM | MEM_RDONLY from bpf_this_cpu_ptr or bpf_per_cpu_ptr
helpers. However, when passing such pointer to kfunc, global funcs, or
BPF helpers, in check_helper_mem_access, there is no expectation
MEM_RDONLY flag will be set, hence it is checked as pointer to writable
memory. Later, verifier sets up argument type of global func as
PTR_TO_MEM | PTR_MAYBE_NULL, so user can use a global func to get around
the limitations imposed by this flag.
This check will also cover global non-percpu variables that may be
introduced in kernel BTF in future.
Also, we update the log message for PTR_TO_BUF case to be similar to
PTR_TO_MEM case, so that the reason for error is clear to user.
Fixes: 34d3a78c681e ("bpf: Make per_cpu_ptr return rdonly PTR_TO_MEM.")
Reviewed-by: Hao Luo <haoluo@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220319080827.73251-3-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e9807e6e1090..d953e62b5268 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4871,13 +4871,23 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno, return check_map_access(env, regno, reg->off, access_size, zero_size_allowed); case PTR_TO_MEM: + if (type_is_rdonly_mem(reg->type)) { + if (meta && meta->raw_mode) { + verbose(env, "R%d cannot write into %s\n", regno, + reg_type_str(env, reg->type)); + return -EACCES; + } + } return check_mem_region_access(env, regno, reg->off, access_size, reg->mem_size, zero_size_allowed); case PTR_TO_BUF: if (type_is_rdonly_mem(reg->type)) { - if (meta && meta->raw_mode) + if (meta && meta->raw_mode) { + verbose(env, "R%d cannot write into %s\n", regno, + reg_type_str(env, reg->type)); return -EACCES; + } max_access = &env->prog->aux->max_rdonly_access; } else { |