Currently, the pointer stored in call->prog_array is loaded in __uprobe_perf_func(), with no RCU annotation and no RCU protection, so 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.

It looks like the intention was to pass a pointer to the member call->prog_array into bpf_prog_run_array_uprobe() and actually dereference the pointer in there. Fix the issue by actually doing that.

Fixes: 8c7dcb84e3b7 ("bpf: implement sleepable uprobes by chaining gps") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn jannh@google.com --- To reproduce, patch include/linux/bpf.h like this: ``` @@ -30,6 +30,7 @@ #include <linux/static_call.h> #include <linux/memcontrol.h> #include <linux/cfi.h> +#include <linux/delay.h>

struct bpf_verifier_env; struct bpf_verifier_log; @@ -2203,6 +2204,7 @@ bpf_prog_run_array_uprobe(const struct bpf_prog_array __rcu *array_rcu, struct bpf_trace_run_ctx run_ctx; u32 ret = 1;

+ mdelay(10000); might_fault();

rcu_read_lock_trace(); ```

Build this userspace program:

``` $ cat dummy.c #include <stdio.h> int main(void) { printf("hello world\n"); } $ gcc -o dummy dummy.c ```

Then build this BPF program and load it (change the path to point to the "dummy" binary you built):

``` $ cat bpf-uprobe-kern.c #include <linux/bpf.h> #include <bpf/bpf_helpers.h> #include <bpf/bpf_tracing.h> char _license[] SEC("license") = "GPL";

SEC("uprobe//home/user/bpf-uprobe-uaf/dummy:main") int BPF_UPROBE(main_uprobe) { bpf_printk("main uprobe triggered\n"); return 0; } $ clang -O2 -g -target bpf -c -o bpf-uprobe-kern.o bpf-uprobe-kern.c $ sudo bpftool prog loadall bpf-uprobe-kern.o uprobe-test autoattach ```

Then run ./dummy in one terminal, and after launching it, run `sudo umount uprobe-test` in another terminal. Once the 10-second mdelay() is over, a use-after-free should occur, which may or may not crash your kernel at the `prog->sleepable` check in bpf_prog_run_array_uprobe() depending on your luck. --- include/linux/bpf.h | 4 ++-- kernel/trace/trace_uprobe.c | 2 +- 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h index eaee2a819f4c150a34a7b1075584711609682e4c..00b3c5b197df75a0386233b9885b480b2ce72f5f 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -2193,7 +2193,7 @@ 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(struct bpf_prog_array __rcu **array_rcu, const void *ctx, bpf_prog_run_fn run_prog) { const struct bpf_prog_array_item *item; @@ -2210,7 +2210,7 @@ bpf_prog_run_array_uprobe(const struct bpf_prog_array __rcu *array_rcu,

run_ctx.is_uprobe = true;

- array = rcu_dereference_check(array_rcu, rcu_read_lock_trace_held()); + 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); diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index fed382b7881b82ee3c334ea77860cce77581a74d..c4eef1eb5ddb3c65205aa9d64af1c72d62fab87f 100644 --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -1404,7 +1404,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu, if (bpf_prog_array_valid(call)) { u32 ret;

- ret = bpf_prog_run_array_uprobe(call->prog_array, regs, bpf_prog_run); + ret = bpf_prog_run_array_uprobe(&call->prog_array, regs, bpf_prog_run); if (!ret) return; }

--- base-commit: 509df676c2d79c985ec2eaa3e3a3bbe557645861 change-id: 20241206-bpf-fix-uprobe-uaf-53d928bab3d0