Re: bpf: BPF_PROG_TEST_RUN leads to unkillable process
From: Y Song <hidden>
Date: 2019-02-04 18:54:20
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On Mon, Feb 4, 2019 at 9:49 AM Stanislav Fomichev [off-list ref] wrote:
On 02/01, Dmitry Vyukov wrote:quoted
Hello, The following program leads to an unkillable process that eats CPU in an infinite loop in BPF_PROG_TEST_RUN syscall. But kernel does not self-detect cpu/rcu/task stalls either. The program contains max number of repetitions, but as far as I see the intention is that it should be killable. I see that bpf_test_run() checks for signal_pending(current), but it does so only if need_resched() is also set. Can need_resched() be not set for prolonged periods of time? /proc/pid/stack is empty, not sure what other info I can provide.There is a bunch of places in the kernel where we do the same nested check: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/broadcom/tg3.c#n12059 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/hw_random/s390-trng.c#n80 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c#n1049 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/s390/crypto/prng.c#n470 So it's not something unusual we do. OTOH, in the kernel/bpf/verifier.c do_check() we do signal_pending() and need_resched() sequentially. In theory, it should not hurt to do them in sequence. Any thoughts about the patch below? I think we also need to properly return -ERESTARTSYS when returning from signal_pending().
I think return value -ERESTARTSYS should be okay.
For the test_run attributes,
struct { /* anonymous struct used by BPF_PROG_TEST_RUN command */
__u32 prog_fd;
__u32 retval;
__u32 data_size_in; /* input: len of data_in */
__u32 data_size_out; /* input/output: len of data_out
* returns ENOSPC if data_out
* is too small.
*/
__aligned_u64 data_in;
__aligned_u64 data_out;
__u32 repeat;
__u32 duration;
} test;
The field data_size_out could be changed during the system call.
But that only happens at bpf_test_finish(). At the time when
-ERESTARTSYS is returned, no attributes have been changed.
quoted hunk ↗ jump to hunk
-- From ce360c909ce4f3caf8eb69f2ad5ce0d3eee1515d Mon Sep 17 00:00:00 2001 Message-Id: [off-list ref] From: Stanislav Fomichev <redacted> Date: Mon, 4 Feb 2019 09:17:37 -0800 Subject: [PATCH bpf] bpf/test_run: properly handle signal_pending Syzbot found out that running BPF_PROG_TEST_RUN with repeat=0xffffffff makes process unkillable. Let's move signal_pending out of need_resched and properly return -ERESTARTSYS to the userspace. In the kernel/bpf/verifier.c do_check() we do: if (signal_pending()) ... if (need_resched()) ... Reported-by: syzbot <redacted> Signed-off-by: Stanislav Fomichev <redacted> --- net/bpf/test_run.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index fa2644d276ef..a891c60cf248 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c@@ -28,12 +28,13 @@ static __always_inline u32 bpf_test_run_one(struct bpf_prog *prog, void *ctx, return ret; } -static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, u32 *ret, - u32 *time) +static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, + u32 *retval, u32 *time) { struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE] = { 0 }; enum bpf_cgroup_storage_type stype; u64 time_start, time_spent = 0; + int ret = 0; u32 i; for_each_cgroup_storage_type(stype) {@@ -50,10 +51,12 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, u32 *ret, repeat = 1; time_start = ktime_get_ns(); for (i = 0; i < repeat; i++) { - *ret = bpf_test_run_one(prog, ctx, storage); + *retval = bpf_test_run_one(prog, ctx, storage); + if (signal_pending(current)) { + ret = -ERESTARTSYS; + break; + } if (need_resched()) { - if (signal_pending(current)) - break; time_spent += ktime_get_ns() - time_start; cond_resched(); time_start = ktime_get_ns();@@ -66,7 +69,7 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, u32 *ret, for_each_cgroup_storage_type(stype) bpf_cgroup_storage_free(storage[stype]); - return 0; + return ret; } static int bpf_test_finish(const union bpf_attr *kattr,quoted
Tested is on upstream commit 4aa9fc2a435abe95a1e8d7f8c7b3d6356514b37a. Config is attached. FTR, generated from the following syzkaller program: r1 = bpf$PROG_LOAD(0x5, &(0x7f0000000080)={0x3, 0x3, &(0x7f0000001fd8)=@framed={{0xffffff85, 0x0, 0x0, 0x0, 0x13, 0x5}}, &(0x7f0000000000)='\x00', 0x5, 0x487, &(0x7f000000cf3d)=""/195}, 0x48) bpf$BPF_PROG_TEST_RUN(0xa, &(0x7f0000000200)={r1, 0x0, 0xe, 0x0, &(0x7f0000000100)="8557147d6187677523fea28c88a8", 0x0, 0xfffffffffffffffe}, 0x28) // autogenerated by syzkaller (https://github.com/google/syzkaller) #define _GNU_SOURCE #include <endian.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/syscall.h> #include <sys/types.h> #include <unistd.h> int main(void) { syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0); long res = 0; *(uint32_t*)0x20000080 = 3; *(uint32_t*)0x20000084 = 3; *(uint64_t*)0x20000088 = 0x20001fd8; *(uint8_t*)0x20001fd8 = 0x85; *(uint8_t*)0x20001fd9 = 0x44; *(uint16_t*)0x20001fda = 0; *(uint32_t*)0x20001fdc = 0x13; *(uint8_t*)0x20001fe0 = 5; *(uint8_t*)0x20001fe1 = 0; *(uint16_t*)0x20001fe2 = 0; *(uint32_t*)0x20001fe4 = 0; *(uint8_t*)0x20001fe8 = 0x95; *(uint8_t*)0x20001fe9 = 0; *(uint16_t*)0x20001fea = 0; *(uint32_t*)0x20001fec = 0; *(uint64_t*)0x20000090 = 0x20000000; memcpy((void*)0x20000000, "\000", 1); *(uint32_t*)0x20000098 = 5; *(uint32_t*)0x2000009c = 0x487; *(uint64_t*)0x200000a0 = 0x2000cf3d; *(uint32_t*)0x200000a8 = 0; *(uint32_t*)0x200000ac = 0; *(uint8_t*)0x200000b0 = 0; *(uint8_t*)0x200000b1 = 0; *(uint8_t*)0x200000b2 = 0; *(uint8_t*)0x200000b3 = 0; *(uint8_t*)0x200000b4 = 0; *(uint8_t*)0x200000b5 = 0; *(uint8_t*)0x200000b6 = 0; *(uint8_t*)0x200000b7 = 0; *(uint8_t*)0x200000b8 = 0; *(uint8_t*)0x200000b9 = 0; *(uint8_t*)0x200000ba = 0; *(uint8_t*)0x200000bb = 0; *(uint8_t*)0x200000bc = 0; *(uint8_t*)0x200000bd = 0; *(uint8_t*)0x200000be = 0; *(uint8_t*)0x200000bf = 0; *(uint32_t*)0x200000c0 = 0; *(uint32_t*)0x200000c4 = 0; int fd = syscall(__NR_bpf, 5, 0x20000080, 0x48); *(uint32_t*)0x20000200 = fd; *(uint32_t*)0x20000204 = 0; *(uint32_t*)0x20000208 = 0xe; *(uint32_t*)0x2000020c = 0; *(uint64_t*)0x20000210 = 0x20000100; memcpy((void*)0x20000100, "\x85\x57\x14\x7d\x61\x87\x67\x75\x23\xfe\xa2\x8c\x88\xa8", 14); *(uint64_t*)0x20000218 = 0; *(uint32_t*)0x20000220 = 0xfffffffe; *(uint32_t*)0x20000224 = 0; syscall(__NR_bpf, 0xa, 0x20000200, 0x28); return 0; }