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bpf: Fix a potential use-after-free #6884

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bpf: Fix a potential use-after-free #6884

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33 changes: 17 additions & 16 deletions kernel/bpf/verifier.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21333,10 +21333,9 @@ static int find_btf_percpu_datasec(struct btf *btf)
}

/*
* Add btf to the used_btfs array and return the index. (If the btf was
* already added, then just return the index.) Upon successful insertion
* increase btf refcnt, and, if present, also refcount the corresponding
* kernel module.
* Add btf to the used_btfs array and return the index. If the btf was
* already added, then just return the index. If needed, refcount the
* corresponding kernel module.
*/
static int __add_used_btf(struct bpf_verifier_env *env, struct btf *btf)
{
Expand All @@ -21354,19 +21353,15 @@ static int __add_used_btf(struct bpf_verifier_env *env, struct btf *btf)
return -E2BIG;
}

btf_get(btf);

btf_mod = &env->used_btfs[env->used_btf_cnt];
btf_mod->btf = btf;
btf_mod->module = NULL;

/* if we reference variables from kernel module, bump its refcount */
if (btf_is_module(btf)) {
btf_mod->module = btf_try_get_module(btf);
if (!btf_mod->module) {
btf_put(btf);
if (!btf_mod->module)
return -ENXIO;
}
}

return env->used_btf_cnt++;
Expand Down Expand Up @@ -21466,9 +21461,7 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,

btf_fd = insn[1].imm;
if (btf_fd) {
CLASS(fd, f)(btf_fd);

btf = __btf_get_by_fd(f);
btf = btf_get_by_fd(btf_fd);
if (IS_ERR(btf)) {
verbose(env, "invalid module BTF object FD specified.\n");
return -EINVAL;
Expand All @@ -21478,17 +21471,23 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
verbose(env, "kernel is missing BTF, make sure CONFIG_DEBUG_INFO_BTF=y is specified in Kconfig.\n");
return -EINVAL;
}
btf_get(btf_vmlinux);
btf = btf_vmlinux;
}

err = __check_pseudo_btf_id(env, insn, aux, btf);
if (err)
return err;
goto err_put;

err = __add_used_btf(env, btf);
if (err < 0)
return err;
goto err_put;

return 0;

err_put:
btf_put(btf);
return err;
}

static bool is_tracing_prog_type(enum bpf_prog_type type)
Expand Down Expand Up @@ -25368,11 +25367,13 @@ static int add_fd_from_fd_array(struct bpf_verifier_env *env, int fd)
return 0;
}

btf = __btf_get_by_fd(f);
btf = btf_get_by_fd(fd);
if (!IS_ERR(btf)) {
err = __add_used_btf(env, btf);
if (err < 0)
if (err < 0) {
btf_put(btf);
return err;
}
return 0;
}

Expand Down
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