• Daniel Borkmann's avatar
    bpf: fix use after free in prog symbol exposure · c751798a
    Daniel Borkmann authored
    syzkaller managed to trigger the warning in bpf_jit_free() which checks via
    bpf_prog_kallsyms_verify_off() for potentially unlinked JITed BPF progs
    in kallsyms, and subsequently trips over GPF when walking kallsyms entries:
    
      [...]
      8021q: adding VLAN 0 to HW filter on device batadv0
      8021q: adding VLAN 0 to HW filter on device batadv0
      WARNING: CPU: 0 PID: 9869 at kernel/bpf/core.c:810 bpf_jit_free+0x1e8/0x2a0
      Kernel panic - not syncing: panic_on_warn set ...
      CPU: 0 PID: 9869 Comm: kworker/0:7 Not tainted 5.0.0-rc8+ #1
      Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
      Workqueue: events bpf_prog_free_deferred
      Call Trace:
       __dump_stack lib/dump_stack.c:77 [inline]
       dump_stack+0x113/0x167 lib/dump_stack.c:113
       panic+0x212/0x40b kernel/panic.c:214
       __warn.cold.8+0x1b/0x38 kernel/panic.c:571
       report_bug+0x1a4/0x200 lib/bug.c:186
       fixup_bug arch/x86/kernel/traps.c:178 [inline]
       do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
       do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
       invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
      RIP: 0010:bpf_jit_free+0x1e8/0x2a0
      Code: 02 4c 89 e2 83 e2 07 38 d0 7f 08 84 c0 0f 85 86 00 00 00 48 ba 00 02 00 00 00 00 ad de 0f b6 43 02 49 39 d6 0f 84 5f fe ff ff <0f> 0b e9 58 fe ff ff 48 b8 00 00 00 00 00 fc ff df 4c 89 e2 48 c1
      RSP: 0018:ffff888092f67cd8 EFLAGS: 00010202
      RAX: 0000000000000007 RBX: ffffc90001947000 RCX: ffffffff816e9d88
      RDX: dead000000000200 RSI: 0000000000000008 RDI: ffff88808769f7f0
      RBP: ffff888092f67d00 R08: fffffbfff1394059 R09: fffffbfff1394058
      R10: fffffbfff1394058 R11: ffffffff89ca02c7 R12: ffffc90001947002
      R13: ffffc90001947020 R14: ffffffff881eca80 R15: ffff88808769f7e8
      BUG: unable to handle kernel paging request at fffffbfff400d000
      #PF error: [normal kernel read fault]
      PGD 21ffee067 P4D 21ffee067 PUD 21ffed067 PMD 9f942067 PTE 0
      Oops: 0000 [#1] PREEMPT SMP KASAN
      CPU: 0 PID: 9869 Comm: kworker/0:7 Not tainted 5.0.0-rc8+ #1
      Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
      Workqueue: events bpf_prog_free_deferred
      RIP: 0010:bpf_get_prog_addr_region kernel/bpf/core.c:495 [inline]
      RIP: 0010:bpf_tree_comp kernel/bpf/core.c:558 [inline]
      RIP: 0010:__lt_find include/linux/rbtree_latch.h:115 [inline]
      RIP: 0010:latch_tree_find include/linux/rbtree_latch.h:208 [inline]
      RIP: 0010:bpf_prog_kallsyms_find+0x107/0x2e0 kernel/bpf/core.c:632
      Code: 00 f0 ff ff 44 38 c8 7f 08 84 c0 0f 85 fa 00 00 00 41 f6 45 02 01 75 02 0f 0b 48 39 da 0f 82 92 00 00 00 48 89 d8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 74 08 3c 03 0f 8e 45 01 00 00 8b 03 48 c1 e0
      [...]
    
    Upon further debugging, it turns out that whenever we trigger this
    issue, the kallsyms removal in bpf_prog_ksym_node_del() was /skipped/
    but yet bpf_jit_free() reported that the entry is /in use/.
    
    Problem is that symbol exposure via bpf_prog_kallsyms_add() but also
    perf_event_bpf_event() were done /after/ bpf_prog_new_fd(). Once the
    fd is exposed to the public, a parallel close request came in right
    before we attempted to do the bpf_prog_kallsyms_add().
    
    Given at this time the prog reference count is one, we start to rip
    everything underneath us via bpf_prog_release() -> bpf_prog_put().
    The memory is eventually released via deferred free, so we're seeing
    that bpf_jit_free() has a kallsym entry because we added it from
    bpf_prog_load() but /after/ bpf_prog_put() from the remote CPU.
    
    Therefore, move both notifications /before/ we install the fd. The
    issue was never seen between bpf_prog_alloc_id() and bpf_prog_new_fd()
    because upon bpf_prog_get_fd_by_id() we'll take another reference to
    the BPF prog, so we're still holding the original reference from the
    bpf_prog_load().
    
    Fixes: 6ee52e2a ("perf, bpf: Introduce PERF_RECORD_BPF_EVENT")
    Fixes: 74451e66 ("bpf: make jited programs visible in traces")
    Reported-by: syzbot+bd3bba6ff3fcea7a6ec6@syzkaller.appspotmail.com
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Cc: Song Liu <songliubraving@fb.com>
    c751798a
syscall.c 67.8 KB