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bpf: Search for kptrs in prog BTF structs

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Currently btf_parse_fields is used in two places to create struct
btf_record's for structs: when looking at mapval type, and when looking
at any struct in program BTF. The former looks for kptr fields while the
latter does not. This patch modifies the btf_parse_fields call made when
looking at prog BTF struct types to search for kptrs as well.

Before this series there was no reason to search for kptrs in non-mapval
types: a referenced kptr needs some owner to guarantee resource cleanup,
and map values were the only owner that supported this. If a struct with
a kptr field were to have some non-kptr-aware owner, the kptr field
might not be properly cleaned up and result in resources leaking. Only
searching for kptr fields in mapval was a simple way to avoid this
problem.

In practice, though, searching for BPF_KPTR when populating
struct_meta_tab does not expose us to this risk, as struct_meta_tab is
only accessed through btf_find_struct_meta helper, and that helper is
only called in contexts where recognizing the kptr field is safe:

  * PTR_TO_BTF_ID reg w/ MEM_ALLOC flag
    * Such a reg is a local kptr and must be free'd via bpf_obj_drop,
      which will correctly handle kptr field

  * When handling specific kfuncs which either expect MEM_ALLOC input or
    return MEM_ALLOC output (obj_{new,drop}, percpu_obj_{new,drop},
    list+rbtree funcs, refcount_acquire)
     * Will correctly handle kptr field for same reasons as above

  * When looking at kptr pointee type
     * Called by functions which implement "correct kptr resource
       handling"

  * In btf_check_and_fixup_fields
     * Helper that ensures no ownership loops for lists and rbtrees,
       doesn't care about kptr field existence

So we should be able to find BPF_KPTR fields in all prog BTF structs
without leaking resources.

Further patches in the series will build on this change to support
kptr_xchg into non-mapval local kptr. Without this change there would be
no kptr field found in such a type.

Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Amery Hung <amery.hung@bytedance.com>
Link: https://lore.kernel.org/r/20240813212424.2871455-3-amery.hung@bytedance.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Dave Marchevsky 2024-08-13 21:24:21 +00:00 committed by Alexei Starovoitov
parent c5ef53420f
commit 7a851ecb18
1 changed files with 53 additions and 19 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

72
kernel/bpf/btf.c
View file

@ -5512,36 +5512,70 @@ static const char *alloc_obj_fields[] = {
static struct btf_struct_metas *
btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
{
union {
struct btf_id_set set;
struct {
u32 _cnt;
u32 _ids[ARRAY_SIZE(alloc_obj_fields)];
} _arr;
} aof;
struct btf_struct_metas *tab = NULL;
struct btf_id_set *aof;
int i, n, id, ret;
BUILD_BUG_ON(offsetof(struct btf_id_set, cnt) != 0);
BUILD_BUG_ON(sizeof(struct btf_id_set) != sizeof(u32));
memset(&aof, 0, sizeof(aof));
aof = kmalloc(sizeof(*aof), GFP_KERNEL | __GFP_NOWARN);
if (!aof)
return ERR_PTR(-ENOMEM);
aof->cnt = 0;
for (i = 0; i < ARRAY_SIZE(alloc_obj_fields); i++) {
/* Try to find whether this special type exists in user BTF, and
* if so remember its ID so we can easily find it among members
* of structs that we iterate in the next loop.
*/
struct btf_id_set *new_aof;
id = btf_find_by_name_kind(btf, alloc_obj_fields[i], BTF_KIND_STRUCT);
if (id < 0)
continue;
aof.set.ids[aof.set.cnt++] = id;
new_aof = krealloc(aof, offsetof(struct btf_id_set, ids[aof->cnt + 1]),
GFP_KERNEL | __GFP_NOWARN);
if (!new_aof) {
ret = -ENOMEM;
goto free_aof;
}
aof = new_aof;
aof->ids[aof->cnt++] = id;
}
if (!aof.set.cnt)
return NULL;
sort(&aof.set.ids, aof.set.cnt, sizeof(aof.set.ids[0]), btf_id_cmp_func, NULL);
n = btf_nr_types(btf);
for (i = 1; i < n; i++) {
/* Try to find if there are kptrs in user BTF and remember their ID */
struct btf_id_set *new_aof;
struct btf_field_info tmp;
const struct btf_type *t;
t = btf_type_by_id(btf, i);
if (!t) {
ret = -EINVAL;
goto free_aof;
}
ret = btf_find_kptr(btf, t, 0, 0, &tmp);
if (ret != BTF_FIELD_FOUND)
continue;
new_aof = krealloc(aof, offsetof(struct btf_id_set, ids[aof->cnt + 1]),
GFP_KERNEL | __GFP_NOWARN);
if (!new_aof) {
ret = -ENOMEM;
goto free_aof;
}
aof = new_aof;
aof->ids[aof->cnt++] = i;
}
if (!aof->cnt)
return NULL;
sort(&aof->ids, aof->cnt, sizeof(aof->ids[0]), btf_id_cmp_func, NULL);
for (i = 1; i < n; i++) {
struct btf_struct_metas *new_tab;
const struct btf_member *member;
@ -5551,17 +5585,13 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
int j, tab_cnt;
t = btf_type_by_id(btf, i);
if (!t) {
ret = -EINVAL;
goto free;
}
if (!__btf_type_is_struct(t))
continue;
cond_resched();
for_each_member(j, t, member) {
if (btf_id_set_contains(&aof.set, member->type))
if (btf_id_set_contains(aof, member->type))
goto parse;
}
continue;
@ -5580,7 +5610,8 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
type = &tab->types[tab->cnt];
type->btf_id = i;
record = btf_parse_fields(btf, t, BPF_SPIN_LOCK | BPF_LIST_HEAD | BPF_LIST_NODE |
BPF_RB_ROOT | BPF_RB_NODE | BPF_REFCOUNT, t->size);
BPF_RB_ROOT | BPF_RB_NODE | BPF_REFCOUNT |
BPF_KPTR, t->size);
/* The record cannot be unset, treat it as an error if so */
if (IS_ERR_OR_NULL(record)) {
ret = PTR_ERR_OR_ZERO(record) ?: -EFAULT;
@ -5589,9 +5620,12 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
type->record = record;
tab->cnt++;
}
kfree(aof);
return tab;
free:
btf_struct_metas_free(tab);
free_aof:
kfree(aof);
return ERR_PTR(ret);
}