On Sat, 2025-03-15 at 04:54 +0900, Kohei Enju wrote: > syzbot reported the following splat [0]. > > In check_atomic_load/store(), register validity is not checked before > atomic_ptr_type_ok(). This causes the out-of-bounds read in is_ctx_reg() > called from atomic_ptr_type_ok() when the register number is MAX_BPF_REG > or greater. > > Add check_reg_arg() before atomic_ptr_type_ok(), and return early when > the register is invalid. > > [0] > BUG: KASAN: slab-out-of-bounds in is_ctx_reg kernel/bpf/verifier.c:6185 [inline] > BUG: KASAN: slab-out-of-bounds in atomic_ptr_type_ok+0x3d7/0x550 kernel/bpf/verifier.c:6223 > Read of size 4 at addr ffff888141b0d690 by task syz-executor143/5842 > > CPU: 1 UID: 0 PID: 5842 Comm: syz-executor143 Not tainted 6.14.0-rc3-syzkaller-gf28214603dc6 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025 > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:94 [inline] > dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 > print_address_description mm/kasan/report.c:408 [inline] > print_report+0x16e/0x5b0 mm/kasan/report.c:521 > kasan_report+0x143/0x180 mm/kasan/report.c:634 > is_ctx_reg kernel/bpf/verifier.c:6185 [inline] > atomic_ptr_type_ok+0x3d7/0x550 kernel/bpf/verifier.c:6223 > check_atomic_store kernel/bpf/verifier.c:7804 [inline] > check_atomic kernel/bpf/verifier.c:7841 [inline] > do_check+0x89dd/0xedd0 kernel/bpf/verifier.c:19334 > do_check_common+0x1678/0x2080 kernel/bpf/verifier.c:22600 > do_check_main kernel/bpf/verifier.c:22691 [inline] > bpf_check+0x165c8/0x1cca0 kernel/bpf/verifier.c:23821 > bpf_prog_load+0x1664/0x20e0 kernel/bpf/syscall.c:2967 > __sys_bpf+0x4ea/0x820 kernel/bpf/syscall.c:5811 > __do_sys_bpf kernel/bpf/syscall.c:5918 [inline] > __se_sys_bpf kernel/bpf/syscall.c:5916 [inline] > __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5916 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7fa3ac86bab9 > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007ffe50fff5f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 > RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fa3ac86bab9 > RDX: 0000000000000094 RSI: 00004000000009c0 RDI: 0000000000000005 > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000006 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001 > </TASK> > > Allocated by task 5842: > kasan_save_stack mm/kasan/common.c:47 [inline] > kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 > poison_kmalloc_redzone mm/kasan/common.c:377 [inline] > __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:394 > kasan_kmalloc include/linux/kasan.h:260 [inline] > __kmalloc_cache_noprof+0x243/0x390 mm/slub.c:4325 > kmalloc_noprof include/linux/slab.h:901 [inline] > kzalloc_noprof include/linux/slab.h:1037 [inline] > do_check_common+0x1ec/0x2080 kernel/bpf/verifier.c:22499 > do_check_main kernel/bpf/verifier.c:22691 [inline] > bpf_check+0x165c8/0x1cca0 kernel/bpf/verifier.c:23821 > bpf_prog_load+0x1664/0x20e0 kernel/bpf/syscall.c:2967 > __sys_bpf+0x4ea/0x820 kernel/bpf/syscall.c:5811 > __do_sys_bpf kernel/bpf/syscall.c:5918 [inline] > __se_sys_bpf kernel/bpf/syscall.c:5916 [inline] > __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5916 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > The buggy address belongs to the object at ffff888141b0d000 > which belongs to the cache kmalloc-2k of size 2048 > The buggy address is located 312 bytes to the right of > allocated 1368-byte region [ffff888141b0d000, ffff888141b0d558) > > The buggy address belongs to the physical page: > page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x141b08 > head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 > flags: 0x57ff00000000040(head|node=1|zone=2|lastcpupid=0x7ff) > page_type: f5(slab) > raw: 057ff00000000040 ffff88801b042000 dead000000000100 dead000000000122 > raw: 0000000000000000 0000000080080008 00000000f5000000 0000000000000000 > head: 057ff00000000040 ffff88801b042000 dead000000000100 dead000000000122 > head: 0000000000000000 0000000080080008 00000000f5000000 0000000000000000 > head: 057ff00000000003 ffffea000506c201 ffffffffffffffff 0000000000000000 > head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000 > page dumped because: kasan: bad access detected > page_owner tracks the page as allocated > page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 8909973200, free_ts 0 > set_page_owner include/linux/page_owner.h:32 [inline] > post_alloc_hook+0x1f4/0x240 mm/page_alloc.c:1585 > prep_new_page mm/page_alloc.c:1593 [inline] > get_page_from_freelist+0x3a8c/0x3c20 mm/page_alloc.c:3538 > __alloc_frozen_pages_noprof+0x264/0x580 mm/page_alloc.c:4805 > alloc_pages_mpol+0x311/0x660 mm/mempolicy.c:2270 > alloc_slab_page mm/slub.c:2423 [inline] > allocate_slab+0x8f/0x3a0 mm/slub.c:2587 > new_slab mm/slub.c:2640 [inline] > ___slab_alloc+0xc27/0x14a0 mm/slub.c:3826 > __slab_alloc+0x58/0xa0 mm/slub.c:3916 > __slab_alloc_node mm/slub.c:3991 [inline] > slab_alloc_node mm/slub.c:4152 [inline] > __kmalloc_cache_noprof+0x27b/0x390 mm/slub.c:4320 > kmalloc_noprof include/linux/slab.h:901 [inline] > kzalloc_noprof include/linux/slab.h:1037 [inline] > virtio_pci_probe+0x54/0x340 drivers/virtio/virtio_pci_common.c:689 > local_pci_probe drivers/pci/pci-driver.c:324 [inline] > pci_call_probe drivers/pci/pci-driver.c:392 [inline] > __pci_device_probe drivers/pci/pci-driver.c:417 [inline] > pci_device_probe+0x6c5/0xa10 drivers/pci/pci-driver.c:451 > really_probe+0x2b9/0xad0 drivers/base/dd.c:658 > __driver_probe_device+0x1a2/0x390 drivers/base/dd.c:800 > driver_probe_device+0x50/0x430 drivers/base/dd.c:830 > __driver_attach+0x45f/0x710 drivers/base/dd.c:1216 > bus_for_each_dev+0x239/0x2b0 drivers/base/bus.c:370 > bus_add_driver+0x346/0x670 drivers/base/bus.c:678 > page_owner free stack trace missing > > Memory state around the buggy address: > ffff888141b0d580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > ffff888141b0d600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > >ffff888141b0d680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > ^ > ffff888141b0d700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > ffff888141b0d780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > > Reported-by: syzbot+a5964227adc0f904549c@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://syzkaller.appspot.com/bug?extid=a5964227adc0f904549c > Tested-by: syzbot+a5964227adc0f904549c@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: e24bbad29a8d ("bpf: Introduce load-acquire and store-release instructions") > Signed-off-by: Kohei Enju <enjuk@xxxxxxxxxx> > --- I wonder if we have test cases for malformed instructions. Maybe add one since this issue was hit? > kernel/bpf/verifier.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 3303a3605ee8..6481604ab612 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -7788,6 +7788,12 @@ static int check_atomic_rmw(struct bpf_verifier_env *env, > static int check_atomic_load(struct bpf_verifier_env *env, > struct bpf_insn *insn) > { > + int err; > + > + err = check_reg_arg(env, insn->src_reg, SRC_OP); > + if (err) > + return err; > + I agree with these changes, however, both check_load_mem() and check_store_reg() already do check_reg_arg() first thing. Maybe just swap the atomic_ptr_type_ok() and check_load_mem()? > if (!atomic_ptr_type_ok(env, insn->src_reg, insn)) { > verbose(env, "BPF_ATOMIC loads from R%d %s is not allowed\n", > insn->src_reg, > @@ -7801,6 +7807,12 @@ static int check_atomic_load(struct bpf_verifier_env *env, > static int check_atomic_store(struct bpf_verifier_env *env, > struct bpf_insn *insn) > { > + int err; > + > + err = check_reg_arg(env, insn->dst_reg, SRC_OP); > + if (err) > + return err; > + > if (!atomic_ptr_type_ok(env, insn->dst_reg, insn)) { > verbose(env, "BPF_ATOMIC stores into R%d %s is not allowed\n", > insn->dst_reg,
