From b90c5d770dad910fb89e6c1b15052a8a1e8db752 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 12:41:58 +0200 Subject: [PATCH] bpf: Preserve inner map identity in callback frames Callback frame constructors initialize map-typed argument registers with __mark_reg_known_zero() and then restore map_ptr. This clears map_uid, which is the only field distinguishing inner maps that share an inner_map_meta template. When a timer callback invokes bpf_for_each_map_elem() on a second inner map, both the saved first map and the second map value can reach the nested callback as the same template with map_uid zero. bpf_timer_init() then accepts pairing the timer from the second map with the first map. The runtime records the first map in the timer without taking a reference. Freeing that map does not find the timer stored in the second map, so a later timer callback dereferences the freed map. Copy map_uid from the same caller register as map_ptr when constructing for-each, timer/workqueue, and task-work callback arguments. The existing identity check can then reject mismatched inner maps while allowing a callback value to be paired with its actual map. Fixes: 3e8ce29850f1 ("bpf: Prevent pointer mismatch in bpf_timer_init.") Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper") Fixes: 5c8fd7e2b5b0 ("bpf: bpf task work plumbing") Reported-by: Nicholas Carlini Suggested-by: Nicholas Carlini Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904104203.345917-8-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b71c5274b3dc..c8699a8831df 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10018,10 +10018,12 @@ int map_set_for_each_callback_args(struct bpf_verifier_env *env, callee->regs[BPF_REG_2].type = PTR_TO_MAP_KEY; __mark_reg_known_zero(&callee->regs[BPF_REG_2]); callee->regs[BPF_REG_2].map_ptr = caller->regs[BPF_REG_1].map_ptr; + callee->regs[BPF_REG_2].map_uid = caller->regs[BPF_REG_1].map_uid; callee->regs[BPF_REG_3].type = PTR_TO_MAP_VALUE; __mark_reg_known_zero(&callee->regs[BPF_REG_3]); callee->regs[BPF_REG_3].map_ptr = caller->regs[BPF_REG_1].map_ptr; + callee->regs[BPF_REG_3].map_uid = caller->regs[BPF_REG_1].map_uid; /* pointer to stack or null */ callee->regs[BPF_REG_4] = caller->regs[BPF_REG_3]; @@ -10099,6 +10101,7 @@ static int set_timer_callback_state(struct bpf_verifier_env *env, int insn_idx) { struct bpf_map *map_ptr = caller->regs[BPF_REG_1].map_ptr; + u32 map_uid = caller->regs[BPF_REG_1].map_uid; /* bpf_timer_set_callback(struct bpf_timer *timer, void *callback_fn); * callback_fn(struct bpf_map *map, void *key, void *value); @@ -10106,14 +10109,17 @@ static int set_timer_callback_state(struct bpf_verifier_env *env, callee->regs[BPF_REG_1].type = CONST_PTR_TO_MAP; __mark_reg_known_zero(&callee->regs[BPF_REG_1]); callee->regs[BPF_REG_1].map_ptr = map_ptr; + callee->regs[BPF_REG_1].map_uid = map_uid; callee->regs[BPF_REG_2].type = PTR_TO_MAP_KEY; __mark_reg_known_zero(&callee->regs[BPF_REG_2]); callee->regs[BPF_REG_2].map_ptr = map_ptr; + callee->regs[BPF_REG_2].map_uid = map_uid; callee->regs[BPF_REG_3].type = PTR_TO_MAP_VALUE; __mark_reg_known_zero(&callee->regs[BPF_REG_3]); callee->regs[BPF_REG_3].map_ptr = map_ptr; + callee->regs[BPF_REG_3].map_uid = map_uid; /* unused */ bpf_mark_reg_not_init(env, &callee->regs[BPF_REG_4]); @@ -10213,6 +10219,7 @@ static int set_task_work_schedule_callback_state(struct bpf_verifier_env *env, int insn_idx) { struct bpf_map *map_ptr = caller->regs[BPF_REG_3].map_ptr; + u32 map_uid = caller->regs[BPF_REG_3].map_uid; /* * callback_fn(struct bpf_map *map, void *key, void *value); @@ -10220,14 +10227,17 @@ static int set_task_work_schedule_callback_state(struct bpf_verifier_env *env, callee->regs[BPF_REG_1].type = CONST_PTR_TO_MAP; __mark_reg_known_zero(&callee->regs[BPF_REG_1]); callee->regs[BPF_REG_1].map_ptr = map_ptr; + callee->regs[BPF_REG_1].map_uid = map_uid; callee->regs[BPF_REG_2].type = PTR_TO_MAP_KEY; __mark_reg_known_zero(&callee->regs[BPF_REG_2]); callee->regs[BPF_REG_2].map_ptr = map_ptr; + callee->regs[BPF_REG_2].map_uid = map_uid; callee->regs[BPF_REG_3].type = PTR_TO_MAP_VALUE; __mark_reg_known_zero(&callee->regs[BPF_REG_3]); callee->regs[BPF_REG_3].map_ptr = map_ptr; + callee->regs[BPF_REG_3].map_uid = map_uid; /* unused */ bpf_mark_reg_not_init(env, &callee->regs[BPF_REG_4]);