diff options
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/verifier.c | 63 |
1 files changed, 51 insertions, 12 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 80dc01350c77..da03bbbc1620 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -19387,13 +19387,29 @@ static bool check_ids(u32 old_id, u32 cur_id, struct bpf_idmap *idmap) return false; } -/* Similar to check_ids(), but allocate a unique temporary ID - * for 'old_id' or 'cur_id' of zero. - * This makes pairs like '0 vs unique ID', 'unique ID vs 0' valid. +/* + * Compare scalar register IDs for state equivalence. + * + * When old_id == 0, the old register is independent - not linked to any + * other register. Any linking in the current state only adds constraints, + * making it more restrictive. Since the old state didn't rely on any ID + * relationships for this register, it's always safe to accept cur regardless + * of its ID. Hence, return true immediately. + * + * When old_id != 0 but cur_id == 0, we need to ensure that different + * independent registers in cur don't incorrectly satisfy the ID matching + * requirements of linked registers in old. + * + * Example: if old has r6.id=X and r7.id=X (linked), but cur has r6.id=0 + * and r7.id=0 (both independent), without temp IDs both would map old_id=X + * to cur_id=0 and pass. With temp IDs: r6 maps X->temp1, r7 tries to map + * X->temp2, but X is already mapped to temp1, so the check fails correctly. */ static bool check_scalar_ids(u32 old_id, u32 cur_id, struct bpf_idmap *idmap) { - old_id = old_id ? old_id : ++idmap->tmp_id_gen; + if (!old_id) + return true; + cur_id = cur_id ? cur_id : ++idmap->tmp_id_gen; return check_ids(old_id, cur_id, idmap); @@ -19618,11 +19634,21 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold, } if (!rold->precise && exact == NOT_EXACT) return true; - if ((rold->id & BPF_ADD_CONST) != (rcur->id & BPF_ADD_CONST)) - return false; - if ((rold->id & BPF_ADD_CONST) && (rold->off != rcur->off)) - return false; - /* Why check_ids() for scalar registers? + /* + * Linked register tracking uses rold->id to detect relationships. + * When rold->id == 0, the register is independent and any linking + * in rcur only adds constraints. When rold->id != 0, we must verify + * id mapping and (for BPF_ADD_CONST) offset consistency. + * + * +------------------+-----------+------------------+---------------+ + * | | rold->id | rold + ADD_CONST | rold->id == 0 | + * |------------------+-----------+------------------+---------------| + * | rcur->id | range,ids | false | range | + * | rcur + ADD_CONST | false | range,ids,off | range | + * | rcur->id == 0 | range,ids | false | range | + * +------------------+-----------+------------------+---------------+ + * + * Why check_ids() for scalar registers? * * Consider the following BPF code: * 1: r6 = ... unbound scalar, ID=a ... @@ -19646,9 +19672,22 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold, * --- * Also verify that new value satisfies old value range knowledge. */ - return range_within(rold, rcur) && - tnum_in(rold->var_off, rcur->var_off) && - check_scalar_ids(rold->id, rcur->id, idmap); + + /* ADD_CONST mismatch: different linking semantics */ + if ((rold->id & BPF_ADD_CONST) && !(rcur->id & BPF_ADD_CONST)) + return false; + + if (rold->id && !(rold->id & BPF_ADD_CONST) && (rcur->id & BPF_ADD_CONST)) + return false; + + /* Both have offset linkage: offsets must match */ + if ((rold->id & BPF_ADD_CONST) && rold->off != rcur->off) + return false; + + if (!check_scalar_ids(rold->id, rcur->id, idmap)) + return false; + + return range_within(rold, rcur) && tnum_in(rold->var_off, rcur->var_off); case PTR_TO_MAP_KEY: case PTR_TO_MAP_VALUE: case PTR_TO_MEM: |