• Jason Gunthorpe's avatar
    IB/uverbs: Get rid of null_obj_type · 3df593bf
    Jason Gunthorpe authored
    If the method fails after calling rdma_explicit_destroy (eg if
    copy_to_user faults) then it will trigger a kernel oops:
    
    BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
    PGD 800000000548d067 P4D 800000000548d067 PUD 54a0067 PMD 0
    SMP PTI
    CPU: 0 PID: 359 Comm: ibv_rc_pingpong Not tainted 4.18.0-rc1+ #28
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
    RIP: 0010:          (null)
    Code: Bad RIP value.
    RSP: 0018:ffffc900001a3bf0 EFLAGS: 00010246
    RAX: 0000000000000000 RBX: ffff88000603bd00 RCX: 0000000000000003
    RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffff88000603bd00
    RBP: 0000000000000001 R08: ffffc900001a3cf8 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000000 R12: ffffc900001a3cf0
    R13: 0000000000000000 R14: ffffc900001a3cf0 R15: 0000000000000000
    FS:  00007fb00dda8700(0000) GS:ffff880007c00000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: ffffffffffffffd6 CR3: 000000000548e004 CR4: 00000000003606b0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     ? rdma_lookup_put_uobject+0x22/0x50 [ib_uverbs]
     ? uverbs_finalize_object+0x3b/0x60 [ib_uverbs]
     ? uverbs_finalize_attrs+0x128/0x140 [ib_uverbs]
     ? ib_uverbs_cmd_verbs+0x698/0x7c0 [ib_uverbs]
     ? find_held_lock+0x2d/0x90
     ? __might_fault+0x39/0x90
     ? ib_uverbs_ioctl+0x111/0x1f0 [ib_uverbs]
     ? do_vfs_ioctl+0xa0/0x6d0
     ? trace_hardirqs_on_caller+0xed/0x180
     ? _raw_spin_unlock_irq+0x24/0x40
     ? syscall_trace_enter+0x138/0x1d0
     ? ksys_ioctl+0x35/0x60
     ? __x64_sys_ioctl+0x11/0x20
     ? do_syscall_64+0x5b/0x1c0
     ? entry_SYSCALL_64_after_hwframe+0x49/0xbe
    
    This is because the type was replaced with the null_type during explicit
    destroy that cannot complete the destruction.
    
    One of the side effects of replacing the type is to make the object
    handle totally unreachable - so no other command could attempt to use
    it, even though it remains on the uboject list.
    
    We can get the same end result by just fully destroying the object inside
    rdma_explicit_destroy and leaving the caller the residual kref for the
    uobj with no attached HW object, and no presence in the ubojects list.
    Signed-off-by: default avatarJason Gunthorpe <jgg@mellanox.com>
    Reviewed-by: default avatarLeon Romanovsky <leonro@mellanox.com>
    3df593bf
rdma_core.c 20.6 KB