[PATCH bpf v3] bpf: Fix theoretical prog_array UAF in __uprobe_perf_func()
STALE661d
From: Jann Horn <jannh@google.com>
Date: 2024-12-10 15:34:29
Also in:
bpf, lkml
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), the rest, tracing · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
Currently, the pointer stored in call->prog_array is loaded in
__uprobe_perf_func(), with no RCU annotation and no immediately visible
RCU protection, so it looks as if the loaded pointer can immediately be
dangling.
Later, bpf_prog_run_array_uprobe() starts a RCU-trace read-side critical
section, but this is too late. It then uses rcu_dereference_check(), but
this use of rcu_dereference_check() does not actually dereference anything.
Fix it by aligning the semantics to bpf_prog_run_array(): Let the caller
provide rcu_read_lock_trace() protection and then load call->prog_array
with rcu_dereference_check().
This issue seems to be theoretical: I don't know of any way to reach this
code without having handle_swbp() further up the stack, which is already
holding a rcu_read_lock_trace() lock, so where we take
rcu_read_lock_trace() in __uprobe_perf_func()/bpf_prog_run_array_uprobe()
doesn't actually have any effect.
Fixes: 8c7dcb84e3b7 ("bpf: implement sleepable uprobes by chaining gps")
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jann Horn <jannh@google.com>
---
Changes in v3:
- align semantics with bpf_prog_run_array()
- correct commit message: the issue is theoretical
- remove stable CC
- Link to v2: https://lore.kernel.org/r/20241206-bpf-fix-uprobe-uaf-v2-1-4c75c54fe424@google.com (local)
Changes in v2:
- remove diff chunk in patch notes that confuses git
- Link to v1: https://lore.kernel.org/r/20241206-bpf-fix-uprobe-uaf-v1-1-6869c8a17258@google.com (local)
---
include/linux/bpf.h | 11 +++--------
kernel/trace/trace_uprobe.c | 6 +++++-
2 files changed, 8 insertions(+), 9 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index eaee2a819f4c150a34a7b1075584711609682e4c..7fe5cf181511d543b1b100028db94ebb2a44da5d 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h@@ -2193,26 +2193,22 @@ bpf_prog_run_array(const struct bpf_prog_array *array, * rcu-protected dynamically sized maps. */ static __always_inline u32 -bpf_prog_run_array_uprobe(const struct bpf_prog_array __rcu *array_rcu, +bpf_prog_run_array_uprobe(const struct bpf_prog_array *array, const void *ctx, bpf_prog_run_fn run_prog) { const struct bpf_prog_array_item *item; const struct bpf_prog *prog; - const struct bpf_prog_array *array; struct bpf_run_ctx *old_run_ctx; struct bpf_trace_run_ctx run_ctx; u32 ret = 1; might_fault(); + RCU_LOCKDEP_WARN(!rcu_read_lock_trace_held(), "no rcu lock held"); - rcu_read_lock_trace(); migrate_disable(); run_ctx.is_uprobe = true; - array = rcu_dereference_check(array_rcu, rcu_read_lock_trace_held()); - if (unlikely(!array)) - goto out; old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx); item = &array->items[0]; while ((prog = READ_ONCE(item->prog))) {
@@ -2227,9 +2223,8 @@ bpf_prog_run_array_uprobe(const struct bpf_prog_array __rcu *array_rcu, rcu_read_unlock(); } bpf_reset_run_ctx(old_run_ctx); -out: + migrate_enable(); - rcu_read_unlock_trace(); return ret; }
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index fed382b7881b82ee3c334ea77860cce77581a74d..4875e7f5de3db249af34c539c079fbedd38f4107 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c@@ -1402,9 +1402,13 @@ static void __uprobe_perf_func(struct trace_uprobe *tu, #ifdef CONFIG_BPF_EVENTS if (bpf_prog_array_valid(call)) { + const struct bpf_prog_array *array; u32 ret; - ret = bpf_prog_run_array_uprobe(call->prog_array, regs, bpf_prog_run); + rcu_read_lock_trace(); + array = rcu_dereference_check(call->prog_array, rcu_read_lock_trace_held()); + ret = bpf_prog_run_array_uprobe(array, regs, bpf_prog_run); + rcu_read_unlock_trace(); if (!ret) return; }
--- base-commit: 509df676c2d79c985ec2eaa3e3a3bbe557645861 change-id: 20241206-bpf-fix-uprobe-uaf-53d928bab3d0 -- Jann Horn [off-list ref]