ucma_process_join() allocates struct ucma_multicast mc and frees it if an
error occurs during its run.  Specifically, if an error occurs in
copy_to_user(), a use-after-free might happen in the following scenario:

1. mc struct is allocated.
2. rdma_join_multicast() is called and succeeds. During its run,
   cma_iboe_join_multicast() enqueues a work that will later use the
   aforementioned mc struct.
3. copy_to_user() is called and fails.
4. mc struct is deallocated.
5. The work that was enqueued by cma_iboe_join_multicast() is run and
   calls ucma_create_uevent() which tries to access mc struct (which is
   freed by now).

Fix this bug by cancelling the work enqueued by cma_iboe_join_multicast().
Since cma_work_handler() frees struct cma_work, we don't use it in
cma_iboe_join_multicast() so we can safely cancel the work later.

The following syzkaller report revealed it:

   BUG: KASAN: use-after-free in ucma_create_uevent+0x2dd/0x;3f0 drivers/infiniband/core/ucma.c:272
   Read of size 8 at addr ffff88810b3ad110 by task kworker/u8:1/108

   CPU: 1 PID: 108 Comm: kworker/u8:1 Not tainted 5.10.0-rc6+ #257
   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS   rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
   Workqueue: rdma_cm cma_work_handler
   Call Trace:
    __dump_stack lib/dump_stack.c:77 [inline]
    dump_stack+0xbe/0xf9 lib/dump_stack.c:118
    print_address_description.constprop.0+0x3e/0×60 mm/kasan/report.c:385
    __kasan_report mm/kasan/report.c:545 [inline]
    kasan_report.cold+0x1f/0×37 mm/kasan/report.c:562
    ucma_create_uevent+0x2dd/0×3f0 drivers/infiniband/core/ucma.c:272
    ucma_event_handler+0xb7/0×3c0 drivers/infiniband/core/ucma.c:349
    cma_cm_event_handler+0x5d/0×1c0 drivers/infiniband/core/cma.c:1977
    cma_work_handler+0xfa/0×190 drivers/infiniband/core/cma.c:2718
    process_one_work+0x54c/0×930 kernel/workqueue.c:2272
    worker_thread+0x82/0×830 kernel/workqueue.c:2418
    kthread+0x1ca/0×220 kernel/kthread.c:292
    ret_from_fork+0x1f/0×30 arch/x86/entry/entry_64.S:296

   Allocated by task 359:
     kasan_save_stack+0x1b/0×40 mm/kasan/common.c:48
     kasan_set_track mm/kasan/common.c:56 [inline]
     __kasan_kmalloc mm/kasan/common.c:461 [inline]
     __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:434
     kmalloc include/linux/slab.h:552 [inline]
     kzalloc include/linux/slab.h:664 [inline]
     ucma_process_join+0x16e/0×3f0 drivers/infiniband/core/ucma.c:1453
     ucma_join_multicast+0xda/0×140 drivers/infiniband/core/ucma.c:1538
     ucma_write+0x1f7/0×280 drivers/infiniband/core/ucma.c:1724
     vfs_write fs/read_write.c:603 [inline]
     vfs_write+0x191/0×4c0 fs/read_write.c:585
     ksys_write+0x1a1/0×1e0 fs/read_write.c:658
     do_syscall_64+0x2d/0×40 arch/x86/entry/common.c:46
     entry_SYSCALL_64_after_hwframe+0x44/0xa9

   Freed by task 359:
     kasan_save_stack+0x1b/0×40 mm/kasan/common.c:48
     kasan_set_track+0x1c/0×30 mm/kasan/common.c:56
     kasan_set_free_info+0x1b/0×30 mm/kasan/generic.c:355
     __kasan_slab_free+0x112/0×160 mm/kasan/common.c:422
     slab_free_hook mm/slub.c:1544 [inline]
     slab_free_freelist_hook mm/slub.c:1577 [inline]
     slab_free mm/slub.c:3142 [inline]
     kfree+0xb3/0×3e0 mm/slub.c:4124
     ucma_process_join+0x22d/0×3f0 drivers/infiniband/core/ucma.c:1497
     ucma_join_multicast+0xda/0×140 drivers/infiniband/core/ucma.c:1538
     ucma_write+0x1f7/0×280 drivers/infiniband/core/ucma.c:1724
     vfs_write fs/read_write.c:603 [inline]
     vfs_write+0x191/0×4c0 fs/read_write.c:585
     ksys_write+0x1a1/0×1e0 fs/read_write.c:658
     do_syscall_64+0x2d/0×40 arch/x86/entry/common.c:46
     entry_SYSCALL_64_after_hwframe+0x44/0xa9
     The buggy address belongs to the object at ffff88810b3ad100
     which belongs to the cache kmalloc-192 of size 192
     The buggy address is located 16 bytes inside of
     192-byte region [ffff88810b3ad100, ffff88810b3ad1c0)

Fixes: b5de0c60 ("RDMA/cma: Fix use after free race in roce multicast join")
Link: https://lore.kernel.org/r/20210211090517.1278415-1-leon@kernel.orgReported-by: Amit Matityahu <mitm@nvidia.com>
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>