On 2/17/21 4:58 AM, Cong Wang wrote:
From: Cong Wang <cong.wang@xxxxxxxxxxxxx> Pretty much similar to commit 1336c662474e ("bpf: Clear per_cpu pointers during bpf_prog_realloc") we also need to clear these two percpu pointers in bpf_prog_clone_create(), otherwise would get a double free: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] SMP PTI CPU: 13 PID: 8140 Comm: kworker/13:247 Kdump: loaded Tainted: G W OE 5.11.0-rc4.bm.1-amd64+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 test_bpf: #1 TXA Workqueue: events bpf_prog_free_deferred RIP: 0010:percpu_ref_get_many.constprop.97+0x42/0xf0 Code: [...] RSP: 0018:ffffa6bce1f9bda0 EFLAGS: 00010002 RAX: 0000000000000001 RBX: 0000000000000000 RCX: 00000000021dfc7b RDX: ffffffffae2eeb90 RSI: 867f92637e338da5 RDI: 0000000000000046 RBP: ffffa6bce1f9bda8 R08: 0000000000000000 R09: 0000000000000001 R10: 0000000000000046 R11: 0000000000000000 R12: 0000000000000280 R13: 0000000000000000 R14: 0000000000000000 R15: ffff9b5f3ffdedc0 FS: 0000000000000000(0000) GS:ffff9b5f2fb40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000027c36c002 CR4: 00000000003706e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: refill_obj_stock+0x5e/0xd0 free_percpu+0xee/0x550 __bpf_prog_free+0x4d/0x60 process_one_work+0x26a/0x590 worker_thread+0x3c/0x390 ? process_one_work+0x590/0x590 kthread+0x130/0x150 ? kthread_park+0x80/0x80 ret_from_fork+0x1f/0x30 This bug is 100% reproducible with test_kmod.sh. Reported-by: Jiang Wang <jiang.wang@xxxxxxxxxxxxx> Fixes: 700d4796ef59 ("bpf: Optimize program stats") Fixes: ca06f55b9002 ("bpf: Add per-program recursion prevention mechanism") Cc: Alexei Starovoitov <ast@xxxxxxxxxx> Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx> --- kernel/bpf/core.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 0ae015ad1e05..b0c11532e535 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1103,6 +1103,8 @@ static struct bpf_prog *bpf_prog_clone_create(struct bpf_prog *fp_other, * this still needs to be adapted. */ memcpy(fp, fp_other, fp_other->pages * PAGE_SIZE); + fp_other->stats = NULL; + fp_other->active = NULL; }return fp;
This is not correct. I presume if you enable blinding and stats, then this will still crash. The proper way to fix it is to NULL these pointers in bpf_prog_clone_free() since the clone can be promoted as the actual prog and the prog ptr released instead. Thanks, Daniel
