On Sun, 4 Dec 2022 at 19:16, pepsipu <soopthegoop@xxxxxxxxx> wrote: > > I believe this is a KASAN bug. > > I made an easier to read version that still triggers KASAN: > > #define _GNU_SOURCE > > #include <stdio.h> > #include <stdlib.h> > #include <string.h> > #include <sys/syscall.h> > #include <sys/types.h> > #include <linux/bpf.h> > #include <unistd.h> > > #include "bpf.h" > > int main(void) > { > __u64 insns[] = { > (BPF_CALL | BPF_JMP) | ((__u64)0x61 << 32), > (BPF_AND | BPF_ALU), > (BPF_EXIT | BPF_JMP), > }; > bpf_load_attr_t load_attr = { > .prog_type = BPF_PROG_TYPE_CGROUP_SKB, > .insn_cnt = sizeof(insns) / sizeof(__u64), > .insns = (__u64)insns, > .license = (__u64) "GPL", > }; > long prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &load_attr, sizeof(bpf_load_attr_t)); > if (prog_fd == -1) > { > printf("could not load bpf prog"); > exit(-1); > } > bpf_trun_attr_t trun_attr = { > .prog_fd = prog_fd, > .data_size_in = 0x81, > .data_size_out = -1, > .data_in = (__u64) "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", > }; > > syscall(__NR_bpf, BPF_PROG_TEST_RUN, &trun_attr, sizeof(bpf_trun_attr_t)); > return 0; > } > > It looks like KASAN believes the tail access of SKB's backing buffer, the SKB shared info struct, allocated by bpf_test_init is out-of-bounds. > This is likely because when the SKB is setup, in build_skb, the tail is calculated as "data + ksize(data) - sizeof(skb_shared_info)". ksize returns the size of the slab, not the allocation, so the tail is much further past the allocation. > However, KASAN is usually supposed to correct for ksize calls by unpoisioning the entire slab it's called on... I'm not sure why this is happening. Hi, [+orignal CC list, please keep it in replies, almost none of relevant receivers read syzkaller-bugs@ mailing list] Also +Kees and kasan-dev for ksize. After the following patch the behavior has changed and KASAN does not unpoison the fail of the object: mm: Make ksize() a reporting-only function https://lore.kernel.org/all/20221118035656.gonna.698-kees@xxxxxxxxxx/ Kees, is this bpf case is a remaining ksize() use that needs to be fixed? > On Monday, November 28, 2022 at 5:42:31 AM UTC-8 syzbot wrote: >> >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: c35bd4e42885 Add linux-next specific files for 20221124 >> git tree: linux-next >> console+strace: https://syzkaller.appspot.com/x/log.txt?x=15e5d7e5880000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=11e19c740a0b2926 >> dashboard link: https://syzkaller.appspot.com/bug?extid=fda18eaa8c12534ccb3b >> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1096f205880000 >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10b2d68d880000 >> >> Downloadable assets: >> disk image: https://storage.googleapis.com/syzbot-assets/968fee464d14/disk-c35bd4e4.raw.xz >> vmlinux: https://storage.googleapis.com/syzbot-assets/4f46fe801b5b/vmlinux-c35bd4e4.xz >> kernel image: https://storage.googleapis.com/syzbot-assets/c2cdf8fb264e/bzImage-c35bd4e4.xz >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+fda18e...@xxxxxxxxxxxxxxxxxxxxxxxxx >> >> ================================================================== >> BUG: KASAN: slab-out-of-bounds in __build_skb_around+0x235/0x340 net/core/skbuff.c:294 >> Write of size 32 at addr ffff88802aa172c0 by task syz-executor413/5295 >> >> CPU: 0 PID: 5295 Comm: syz-executor413 Not tainted 6.1.0-rc6-next-20221124-syzkaller #0 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022 >> Call Trace: >> <TASK> >> __dump_stack lib/dump_stack.c:88 [inline] >> dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106 >> print_address_description mm/kasan/report.c:253 [inline] >> print_report+0x15e/0x45d mm/kasan/report.c:364 >> kasan_report+0xbf/0x1f0 mm/kasan/report.c:464 >> check_region_inline mm/kasan/generic.c:183 [inline] >> kasan_check_range+0x141/0x190 mm/kasan/generic.c:189 >> memset+0x24/0x50 mm/kasan/shadow.c:44 >> __build_skb_around+0x235/0x340 net/core/skbuff.c:294 >> __build_skb+0x4f/0x60 net/core/skbuff.c:328 >> build_skb+0x22/0x280 net/core/skbuff.c:340 >> bpf_prog_test_run_skb+0x343/0x1e10 net/bpf/test_run.c:1131 >> bpf_prog_test_run kernel/bpf/syscall.c:3644 [inline] >> __sys_bpf+0x1599/0x4ff0 kernel/bpf/syscall.c:4997 >> __do_sys_bpf kernel/bpf/syscall.c:5083 [inline] >> __se_sys_bpf kernel/bpf/syscall.c:5081 [inline] >> __x64_sys_bpf+0x79/0xc0 kernel/bpf/syscall.c:5081 >> do_syscall_x64 arch/x86/entry/common.c:50 [inline] >> do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 >> entry_SYSCALL_64_after_hwframe+0x63/0xcd >> RIP: 0033:0x7f30de9aad19 >> Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48 >> RSP: 002b:00007ffeaee34318 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 >> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f30de9aad19 >> RDX: 0000000000000028 RSI: 0000000020000180 RDI: 000000000000000a >> RBP: 00007f30de96eec0 R08: 0000000000000000 R09: 0000000000000000 >> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f30de96ef50 >> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 >> </TASK> >> >> Allocated by task 5295: >> kasan_save_stack+0x22/0x40 mm/kasan/common.c:45 >> kasan_set_track+0x25/0x30 mm/kasan/common.c:52 >> ____kasan_kmalloc mm/kasan/common.c:376 [inline] >> ____kasan_kmalloc mm/kasan/common.c:335 [inline] >> __kasan_kmalloc+0xa5/0xb0 mm/kasan/common.c:385 >> kasan_kmalloc include/linux/kasan.h:212 [inline] >> __do_kmalloc_node mm/slab_common.c:955 [inline] >> __kmalloc+0x5a/0xd0 mm/slab_common.c:968 >> kmalloc include/linux/slab.h:575 [inline] >> kzalloc include/linux/slab.h:711 [inline] >> bpf_test_init.isra.0+0xa5/0x150 net/bpf/test_run.c:778 >> bpf_prog_test_run_skb+0x22e/0x1e10 net/bpf/test_run.c:1097 >> bpf_prog_test_run kernel/bpf/syscall.c:3644 [inline] >> __sys_bpf+0x1599/0x4ff0 kernel/bpf/syscall.c:4997 >> __do_sys_bpf kernel/bpf/syscall.c:5083 [inline] >> __se_sys_bpf kernel/bpf/syscall.c:5081 [inline] >> __x64_sys_bpf+0x79/0xc0 kernel/bpf/syscall.c:5081 >> do_syscall_x64 arch/x86/entry/common.c:50 [inline] >> do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 >> entry_SYSCALL_64_after_hwframe+0x63/0xcd >> >> The buggy address belongs to the object at ffff88802aa17000 >> which belongs to the cache kmalloc-1k of size 1024 >> The buggy address is located 704 bytes inside of >> 1024-byte region [ffff88802aa17000, ffff88802aa17400) >> >> The buggy address belongs to the physical page: >> page:ffffea0000aa8400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2aa10 >> head:ffffea0000aa8400 order:3 compound_mapcount:0 subpages_mapcount:0 compound_pincount:0 >> flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff) >> raw: 00fff00000010200 ffff888012441dc0 dead000000000122 0000000000000000 >> raw: 0000000000000000 0000000080100010 00000001ffffffff 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 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5295, tgid 5295 (strace-static-x), ts 57049914920, free_ts 56991966201 >> prep_new_page mm/page_alloc.c:2541 [inline] >> get_page_from_freelist+0x119c/0x2cd0 mm/page_alloc.c:4293 >> __alloc_pages+0x1cb/0x5b0 mm/page_alloc.c:5551 >> alloc_pages+0x1aa/0x270 mm/mempolicy.c:2285 >> alloc_slab_page mm/slub.c:1833 [inline] >> allocate_slab+0x25e/0x350 mm/slub.c:1980 >> new_slab mm/slub.c:2033 [inline] >> ___slab_alloc+0xa91/0x1400 mm/slub.c:3211 >> __slab_alloc.constprop.0+0x56/0xa0 mm/slub.c:3310 >> slab_alloc_node mm/slub.c:3395 [inline] >> __kmem_cache_alloc_node+0x1a9/0x430 mm/slub.c:3472 >> __do_kmalloc_node mm/slab_common.c:954 [inline] >> __kmalloc+0x4a/0xd0 mm/slab_common.c:968 >> kmalloc include/linux/slab.h:575 [inline] >> kzalloc include/linux/slab.h:711 [inline] >> tomoyo_init_log+0x1282/0x1ec0 security/tomoyo/audit.c:275 >> tomoyo_supervisor+0x354/0xf10 security/tomoyo/common.c:2088 >> tomoyo_audit_env_log security/tomoyo/environ.c:36 [inline] >> tomoyo_env_perm+0x183/0x200 security/tomoyo/environ.c:63 >> tomoyo_environ security/tomoyo/domain.c:672 [inline] >> tomoyo_find_next_domain+0x13d2/0x1f80 security/tomoyo/domain.c:879 >> tomoyo_bprm_check_security security/tomoyo/tomoyo.c:101 [inline] >> tomoyo_bprm_check_security+0x133/0x1c0 security/tomoyo/tomoyo.c:91 >> security_bprm_check+0x49/0xb0 security/security.c:897 >> search_binary_handler fs/exec.c:1723 [inline] >> exec_binprm fs/exec.c:1777 [inline] >> bprm_execve fs/exec.c:1851 [inline] >> bprm_execve+0x732/0x19f0 fs/exec.c:1808 >> do_execveat_common+0x724/0x890 fs/exec.c:1956 >> page last free stack trace: >> reset_page_owner include/linux/page_owner.h:24 [inline] >> free_pages_prepare mm/page_alloc.c:1448 [inline] >> free_pcp_prepare+0x65c/0xc00 mm/page_alloc.c:1498 >> free_unref_page_prepare mm/page_alloc.c:3379 [inline] >> free_unref_page+0x1d/0x490 mm/page_alloc.c:3474 >> __unfreeze_partials+0x17c/0x1a0 mm/slub.c:2617 >> qlink_free mm/kasan/quarantine.c:168 [inline] >> qlist_free_all+0x6a/0x170 mm/kasan/quarantine.c:187 >> kasan_quarantine_reduce+0x192/0x220 mm/kasan/quarantine.c:294 >> __kasan_slab_alloc+0x66/0x90 mm/kasan/common.c:307 >> kasan_slab_alloc include/linux/kasan.h:202 [inline] >> slab_post_alloc_hook mm/slab.h:761 [inline] >> slab_alloc_node mm/slub.c:3433 [inline] >> slab_alloc mm/slub.c:3441 [inline] >> __kmem_cache_alloc_lru mm/slub.c:3448 [inline] >> kmem_cache_alloc+0x1e3/0x430 mm/slub.c:3457 >> vm_area_alloc+0x20/0x100 kernel/fork.c:458 >> mmap_region+0x44c/0x1dd0 mm/mmap.c:2605 >> do_mmap+0x831/0xf60 mm/mmap.c:1412 >> vm_mmap_pgoff+0x1af/0x280 mm/util.c:520 >> ksys_mmap_pgoff+0x7d/0x5a0 mm/mmap.c:1458 >> do_syscall_x64 arch/x86/entry/common.c:50 [inline] >> do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 >> entry_SYSCALL_64_after_hwframe+0x63/0xcd >> >> Memory state around the buggy address: >> ffff88802aa17180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> ffff88802aa17200: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc >> >ffff88802aa17280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> ^ >> ffff88802aa17300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> ffff88802aa17380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> ================================================================== >> >> >> --- >> This report is generated by a bot. It may contain errors. >> See https://goo.gl/tpsmEJ for more information about syzbot. >> syzbot engineers can be reached at syzk...@xxxxxxxxxxxxxxxx. >> >> syzbot will keep track of this issue. See: >> https://goo.gl/tpsmEJ#status for how to communicate with syzbot. >> syzbot can test patches for this issue, for details see: >> https://goo.gl/tpsmEJ#testing-patches