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bpf: Preserve inner map identity in callback frames

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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: 3e8ce29850 ("bpf: Prevent pointer mismatch in bpf_timer_init.")
Fixes: 69c087ba62 ("bpf: Add bpf_for_each_map_elem() helper")
Fixes: 5c8fd7e2b5 ("bpf: bpf task work plumbing")
Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-8-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi
2026-09-04 12:41:58 +02:00
committed by Alexei Starovoitov
parent 9dcddf30ac
commit b90c5d770d
1 changed files with 10 additions and 0 deletions
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10
kernel/bpf/verifier.c
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@@ -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]);