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Fri, 06 Dec 2024 12:37:15 -0800 (PST) Received: from localhost ([2a00:79e0:9d:4:a1dd:6aeb:389c:7fd7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-434da113580sm68044935e9.29.2024.12.06.12.37.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Dec 2024 12:37:15 -0800 (PST) From: Jann Horn Date: Fri, 06 Dec 2024 21:37:03 +0100 Subject: [PATCH bpf] bpf: Fix prog_array UAF in __uprobe_perf_func() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20241206-bpf-fix-uprobe-uaf-v1-1-6869c8a17258@google.com> X-B4-Tracking: v=1; b=H4sIAG5gU2cC/x2MywqAIBAAfyX23ILZg+pXooPmWnsxUYpA+veWj gMzUyBTYsowVwUS3Zz5DAJNXcF2mLATshMGrXTXaDWgjR49P3jFdFrCy3jsWzfp0RrbOgUSxkR i/NMFxIf1fT/C+iYdaQAAAA== X-Change-ID: 20241206-bpf-fix-uprobe-uaf-53d928bab3d0 To: Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Delyan Kratunov Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, stable@vger.kernel.org, Jann Horn X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=ed25519-sha256; t=1733517431; l=4088; i=jannh@google.com; s=20240730; h=from:subject:message-id; bh=I8QH9yYP8JFwTKjCJAr/bedB4BBTOAmbOlClo2ps5zc=; b=ZuTXS1DTUtz9mwoP4jNWFIU2COR0aiA3HNcppch70BVqp7JPyDymwr8qZ82Qsf93jBM00n2VV xYabNIwirl+Bjfjh+gZiz1qDfsWSixzTsMnVf/p0fpHYxxcAVSaIGJi X-Developer-Key: i=jannh@google.com; a=ed25519; pk=AljNtGOzXeF6khBXDJVVvwSEkVDGnnZZYqfWhP1V+C8= 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 --- To reproduce, patch include/linux/bpf.h like this: ``` @@ -30,6 +30,7 @@ #include #include #include +#include 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 =3D 1; + mdelay(10000); might_fault(); rcu_read_lock_trace(); ``` Build this userspace program: ``` $ cat dummy.c #include 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 #include #include char _license[] SEC("license") =3D "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..00b3c5b197df75a0386233b9885= b480b2ce72f5f 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, =20 run_ctx.is_uprobe =3D true; =20 - array =3D rcu_dereference_check(array_rcu, rcu_read_lock_trace_held()); + array =3D rcu_dereference_check(*array_rcu, rcu_read_lock_trace_held()); if (unlikely(!array)) goto out; old_run_ctx =3D bpf_set_run_ctx(&run_ctx.run_ctx); diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index fed382b7881b82ee3c334ea77860cce77581a74d..c4eef1eb5ddb3c65205aa9d64af= 1c72d62fab87f 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 *t= u, if (bpf_prog_array_valid(call)) { u32 ret; =20 - ret =3D bpf_prog_run_array_uprobe(call->prog_array, regs, bpf_prog_run); + ret =3D 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 --=20 Jann Horn