On Mon, Mar 25, 2024 at 10:27 AM Andrii Nakryiko
[off-list ref] wrote:

On Sun, Mar 24, 2024 at 5:07 PM Alexei Starovoitov
[off-list ref] wrote:

quoted

Hi Andrii,

syzbot found UAF in raw_tp cookie series in bpf-next.
Reverting the whole merge
2e244a72cd48 ("Merge branch 'bpf-raw-tracepoint-support-for-bpf-cookie'")

fixes the issue.

Pls take a look.
See C reproducer below. It splats consistently with CONFIG_KASAN=y

Thanks.

Will do, traveling today, so will be offline for a bit, but will check
first thing afterwards.

Ok, so I don't think it's bpf_raw_tp_link specific, it should affect a
bunch of other links (unless I missed something). Basically, when last
link refcnt drops, we detach, do bpf_prog_put() and then proceed to
kfree link itself synchronously. But that link can still be referred
from running BPF program (I think multi-kprobe/multi-uprobe use it for
cookies, raw_tp with my changes started using link at runtime, there
are probably more types), and so if we free this memory synchronously,
we can have UAF.

We should do what we do for bpf_maps and delay freeing, the only
question is how tunable that freeing can be? Always do call_rcu()?
Always call_rcu_tasks_trace() (relevant for sleepable multi-uprobes)?
Should we allow synchronous free if link is not directly accessible
from program during its run?

Anyway, I sent a fix as an RFC so we can discuss.

quoted

On Sun, Mar 24, 2024 at 4:28 PM syzbot
[off-list ref] wrote:

quoted

Hello,

syzbot found the following issue on:

HEAD commit:    520fad2e3206 selftests/bpf: scale benchmark counting by us..
git tree:       bpf-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=105af946180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6fb1be60a193d440
dashboard link: https://syzkaller.appspot.com/bug?extid=981935d9485a560bfbcb
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=114f17a5180000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=162bb7a5180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4eef3506c5ce/disk-520fad2e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/24d60ebe76cc/vmlinux-520fad2e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8f883e706550/bzImage-520fad2e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+981935d9485a560bfbcb@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in __bpf_trace_run kernel/trace/bpf_trace.c:2376 [inline]
BUG: KASAN: slab-use-after-free in bpf_trace_run1+0xcb/0x510 kernel/trace/bpf_trace.c:2430
Read of size 8 at addr ffff8880290d9918 by task migration/0/19

CPU: 0 PID: 19 Comm: migration/0 Not tainted 6.8.0-syzkaller-05233-g520fad2e3206 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
Stopper: 0x0 <- 0x0
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:488
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 __bpf_trace_run kernel/trace/bpf_trace.c:2376 [inline]
 bpf_trace_run1+0xcb/0x510 kernel/trace/bpf_trace.c:2430
 __traceiter_rcu_utilization+0x74/0xb0 include/trace/events/rcu.h:27
 trace_rcu_utilization+0x194/0x1c0 include/trace/events/rcu.h:27
 rcu_note_context_switch+0xc7c/0xff0 kernel/rcu/tree_plugin.h:360
 __schedule+0x345/0x4a20 kernel/sched/core.c:6635
 __schedule_loop kernel/sched/core.c:6813 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6828
 smpboot_thread_fn+0x61e/0xa30 kernel/smpboot.c:160
 kthread+0x2f0/0x390 kernel/kthread.c:388
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
 </TASK>

Allocated by task 5075:
 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:370 [inline]
 __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:387
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 kmalloc_trace+0x1d9/0x360 mm/slub.c:4012
 kmalloc include/linux/slab.h:590 [inline]
 kzalloc include/linux/slab.h:711 [inline]
 bpf_raw_tp_link_attach+0x2a0/0x6e0 kernel/bpf/syscall.c:3816
 bpf_raw_tracepoint_open+0x1c2/0x240 kernel/bpf/syscall.c:3863
 __sys_bpf+0x3c0/0x810 kernel/bpf/syscall.c:5673
 __do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5736
 do_syscall_64+0xfb/0x240
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Freed by task 5075:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:589
 poison_slab_object+0xa6/0xe0 mm/kasan/common.c:240
 __kasan_slab_free+0x37/0x60 mm/kasan/common.c:256
 kasan_slab_free include/linux/kasan.h:184 [inline]
 slab_free_hook mm/slub.c:2121 [inline]
 slab_free mm/slub.c:4299 [inline]
 kfree+0x14a/0x380 mm/slub.c:4409
 bpf_link_release+0x3b/0x50 kernel/bpf/syscall.c:3071
 __fput+0x429/0x8a0 fs/file_table.c:423
 task_work_run+0x24f/0x310 kernel/task_work.c:180
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xa1b/0x27e0 kernel/exit.c:878
 do_group_exit+0x207/0x2c0 kernel/exit.c:1027
 __do_sys_exit_group kernel/exit.c:1038 [inline]
 __se_sys_exit_group kernel/exit.c:1036 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1036
 do_syscall_64+0xfb/0x240
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

The buggy address belongs to the object at ffff8880290d9900
 which belongs to the cache kmalloc-128 of size 128
The buggy address is located 24 bytes inside of
 freed 128-byte region [ffff8880290d9900, ffff8880290d9980)

The buggy address belongs to the physical page:
page:ffffea0000a43640 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x290d9
anon flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000800 ffff888014c418c0 0000000000000000 0000000000000001
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 4527, tgid 4527 (udevd), ts 43150902736, free_ts 43094996342
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1ea/0x210 mm/page_alloc.c:1533
 prep_new_page mm/page_alloc.c:1540 [inline]
 get_page_from_freelist+0x33ea/0x3580 mm/page_alloc.c:3311
 __alloc_pages+0x256/0x680 mm/page_alloc.c:4569
 __alloc_pages_node include/linux/gfp.h:238 [inline]
 alloc_pages_node include/linux/gfp.h:261 [inline]
 alloc_slab_page+0x5f/0x160 mm/slub.c:2190
 allocate_slab mm/slub.c:2354 [inline]
 new_slab+0x84/0x2f0 mm/slub.c:2407
 ___slab_alloc+0xd1b/0x13e0 mm/slub.c:3540
 __slab_alloc mm/slub.c:3625 [inline]
 __slab_alloc_node mm/slub.c:3678 [inline]
 slab_alloc_node mm/slub.c:3850 [inline]
 kmalloc_trace+0x267/0x360 mm/slub.c:4007
 kmalloc include/linux/slab.h:590 [inline]
 kzalloc include/linux/slab.h:711 [inline]
 kernfs_get_open_node fs/kernfs/file.c:523 [inline]
 kernfs_fop_open+0x803/0xcd0 fs/kernfs/file.c:691
 do_dentry_open+0x907/0x15a0 fs/open.c:956
 do_open fs/namei.c:3643 [inline]
 path_openat+0x2860/0x3240 fs/namei.c:3800
 do_filp_open+0x235/0x490 fs/namei.c:3827
 do_sys_openat2+0x13e/0x1d0 fs/open.c:1407
 do_sys_open fs/open.c:1422 [inline]
 __do_sys_openat fs/open.c:1438 [inline]
 __se_sys_openat fs/open.c:1433 [inline]
 __x64_sys_openat+0x247/0x2a0 fs/open.c:1433
 do_syscall_64+0xfb/0x240
 entry_SYSCALL_64_after_hwframe+0x6d/0x75
page last free pid 4526 tgid 4526 stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1140 [inline]
 free_unref_page_prepare+0x968/0xa90 mm/page_alloc.c:2346
 free_unref_page+0x37/0x3f0 mm/page_alloc.c:2486
 rcu_do_batch kernel/rcu/tree.c:2196 [inline]
 rcu_core+0xafd/0x1830 kernel/rcu/tree.c:2471
 __do_softirq+0x2bc/0x943 kernel/softirq.c:554

Memory state around the buggy address:
 ffff8880290d9800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880290d9880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

quoted

ffff8880290d9900: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

                            ^
 ffff8880290d9980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880290d9a00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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