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    Subject[PATCH 5.18 200/339] bpf, arm64: Clear prog->jited_len along prog->jited
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 10f3b29c65bb2fe0d47c2945cd0b4087be1c5218 ]

    syzbot reported an illegal copy_to_user() attempt
    from bpf_prog_get_info_by_fd() [1]

    There was no repro yet on this bug, but I think
    that commit 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns")
    is exposing a prior bug in bpf arm64.

    bpf_prog_get_info_by_fd() looks at prog->jited_len
    to determine if the JIT image can be copied out to user space.

    My theory is that syzbot managed to get a prog where prog->jited_len
    has been set to 43, while prog->bpf_func has ben cleared.

    It is not clear why copy_to_user(uinsns, NULL, ulen) is triggering
    this particular warning.

    I thought find_vma_area(NULL) would not find a vm_struct.
    As we do not hold vmap_area_lock spinlock, it might be possible
    that the found vm_struct was garbage.

    [1]
    usercopy: Kernel memory exposure attempt detected from vmalloc (offset 792633534417210172, size 43)!
    kernel BUG at mm/usercopy.c:101!
    Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
    Modules linked in:
    CPU: 0 PID: 25002 Comm: syz-executor.1 Not tainted 5.18.0-syzkaller-10139-g8291eaafed36 #0
    Hardware name: linux,dummy-virt (DT)
    pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
    pc : usercopy_abort+0x90/0x94 mm/usercopy.c:101
    lr : usercopy_abort+0x90/0x94 mm/usercopy.c:89
    sp : ffff80000b773a20
    x29: ffff80000b773a30 x28: faff80000b745000 x27: ffff80000b773b48
    x26: 0000000000000000 x25: 000000000000002b x24: 0000000000000000
    x23: 00000000000000e0 x22: ffff80000b75db67 x21: 0000000000000001
    x20: 000000000000002b x19: ffff80000b75db3c x18: 00000000fffffffd
    x17: 2820636f6c6c616d x16: 76206d6f72662064 x15: 6574636574656420
    x14: 74706d6574746120 x13: 2129333420657a69 x12: 73202c3237313031
    x11: 3237313434333533 x10: 3336323937207465 x9 : 657275736f707865
    x8 : ffff80000a30c550 x7 : ffff80000b773830 x6 : ffff80000b773830
    x5 : 0000000000000000 x4 : ffff00007fbbaa10 x3 : 0000000000000000
    x2 : 0000000000000000 x1 : f7ff000028fc0000 x0 : 0000000000000064
    Call trace:
    usercopy_abort+0x90/0x94 mm/usercopy.c:89
    check_heap_object mm/usercopy.c:186 [inline]
    __check_object_size mm/usercopy.c:252 [inline]
    __check_object_size+0x198/0x36c mm/usercopy.c:214
    check_object_size include/linux/thread_info.h:199 [inline]
    check_copy_size include/linux/thread_info.h:235 [inline]
    copy_to_user include/linux/uaccess.h:159 [inline]
    bpf_prog_get_info_by_fd.isra.0+0xf14/0xfdc kernel/bpf/syscall.c:3993
    bpf_obj_get_info_by_fd+0x12c/0x510 kernel/bpf/syscall.c:4253
    __sys_bpf+0x900/0x2150 kernel/bpf/syscall.c:4956
    __do_sys_bpf kernel/bpf/syscall.c:5021 [inline]
    __se_sys_bpf kernel/bpf/syscall.c:5019 [inline]
    __arm64_sys_bpf+0x28/0x40 kernel/bpf/syscall.c:5019
    __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
    invoke_syscall+0x48/0x114 arch/arm64/kernel/syscall.c:52
    el0_svc_common.constprop.0+0x44/0xec arch/arm64/kernel/syscall.c:142
    do_el0_svc+0xa0/0xc0 arch/arm64/kernel/syscall.c:206
    el0_svc+0x44/0xb0 arch/arm64/kernel/entry-common.c:624
    el0t_64_sync_handler+0x1ac/0x1b0 arch/arm64/kernel/entry-common.c:642
    el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:581
    Code: aa0003e3 d00038c0 91248000 97fff65f (d4210000)

    Fixes: db496944fdaa ("bpf: arm64: add JIT support for multi-function programs")
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Acked-by: Song Liu <songliubraving@fb.com>
    Link: https://lore.kernel.org/bpf/20220531215113.1100754-1-eric.dumazet@gmail.com
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/arm64/net/bpf_jit_comp.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
    index fcc675aa1670..c779e604edac 100644
    --- a/arch/arm64/net/bpf_jit_comp.c
    +++ b/arch/arm64/net/bpf_jit_comp.c
    @@ -1261,6 +1261,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
    bpf_jit_binary_free(header);
    prog->bpf_func = NULL;
    prog->jited = 0;
    + prog->jited_len = 0;
    goto out_off;
    }
    bpf_jit_binary_lock_ro(header);
    --
    2.35.1


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