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    Subject[PATCH 5.15 013/262] cifs: fix double free race when mount fails in cifs_get_root()
    Date
    From: Ronnie Sahlberg <lsahlber@redhat.com>

    [ Upstream commit 3d6cc9898efdfb062efb74dc18cfc700e082f5d5 ]

    When cifs_get_root() fails during cifs_smb3_do_mount() we call
    deactivate_locked_super() which eventually will call delayed_free() which
    will free the context.
    In this situation we should not proceed to enter the out: section in
    cifs_smb3_do_mount() and free the same resources a second time.

    [Thu Feb 10 12:59:06 2022] BUG: KASAN: use-after-free in rcu_cblist_dequeue+0x32/0x60
    [Thu Feb 10 12:59:06 2022] Read of size 8 at addr ffff888364f4d110 by task swapper/1/0

    [Thu Feb 10 12:59:06 2022] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G OE 5.17.0-rc3+ #4
    [Thu Feb 10 12:59:06 2022] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.0 12/17/2019
    [Thu Feb 10 12:59:06 2022] Call Trace:
    [Thu Feb 10 12:59:06 2022] <IRQ>
    [Thu Feb 10 12:59:06 2022] dump_stack_lvl+0x5d/0x78
    [Thu Feb 10 12:59:06 2022] print_address_description.constprop.0+0x24/0x150
    [Thu Feb 10 12:59:06 2022] ? rcu_cblist_dequeue+0x32/0x60
    [Thu Feb 10 12:59:06 2022] kasan_report.cold+0x7d/0x117
    [Thu Feb 10 12:59:06 2022] ? rcu_cblist_dequeue+0x32/0x60
    [Thu Feb 10 12:59:06 2022] __asan_load8+0x86/0xa0
    [Thu Feb 10 12:59:06 2022] rcu_cblist_dequeue+0x32/0x60
    [Thu Feb 10 12:59:06 2022] rcu_core+0x547/0xca0
    [Thu Feb 10 12:59:06 2022] ? call_rcu+0x3c0/0x3c0
    [Thu Feb 10 12:59:06 2022] ? __this_cpu_preempt_check+0x13/0x20
    [Thu Feb 10 12:59:06 2022] ? lock_is_held_type+0xea/0x140
    [Thu Feb 10 12:59:06 2022] rcu_core_si+0xe/0x10
    [Thu Feb 10 12:59:06 2022] __do_softirq+0x1d4/0x67b
    [Thu Feb 10 12:59:06 2022] __irq_exit_rcu+0x100/0x150
    [Thu Feb 10 12:59:06 2022] irq_exit_rcu+0xe/0x30
    [Thu Feb 10 12:59:06 2022] sysvec_hyperv_stimer0+0x9d/0xc0
    ...
    [Thu Feb 10 12:59:07 2022] Freed by task 58179:
    [Thu Feb 10 12:59:07 2022] kasan_save_stack+0x26/0x50
    [Thu Feb 10 12:59:07 2022] kasan_set_track+0x25/0x30
    [Thu Feb 10 12:59:07 2022] kasan_set_free_info+0x24/0x40
    [Thu Feb 10 12:59:07 2022] ____kasan_slab_free+0x137/0x170
    [Thu Feb 10 12:59:07 2022] __kasan_slab_free+0x12/0x20
    [Thu Feb 10 12:59:07 2022] slab_free_freelist_hook+0xb3/0x1d0
    [Thu Feb 10 12:59:07 2022] kfree+0xcd/0x520
    [Thu Feb 10 12:59:07 2022] cifs_smb3_do_mount+0x149/0xbe0 [cifs]
    [Thu Feb 10 12:59:07 2022] smb3_get_tree+0x1a0/0x2e0 [cifs]
    [Thu Feb 10 12:59:07 2022] vfs_get_tree+0x52/0x140
    [Thu Feb 10 12:59:07 2022] path_mount+0x635/0x10c0
    [Thu Feb 10 12:59:07 2022] __x64_sys_mount+0x1bf/0x210
    [Thu Feb 10 12:59:07 2022] do_syscall_64+0x5c/0xc0
    [Thu Feb 10 12:59:07 2022] entry_SYSCALL_64_after_hwframe+0x44/0xae

    [Thu Feb 10 12:59:07 2022] Last potentially related work creation:
    [Thu Feb 10 12:59:07 2022] kasan_save_stack+0x26/0x50
    [Thu Feb 10 12:59:07 2022] __kasan_record_aux_stack+0xb6/0xc0
    [Thu Feb 10 12:59:07 2022] kasan_record_aux_stack_noalloc+0xb/0x10
    [Thu Feb 10 12:59:07 2022] call_rcu+0x76/0x3c0
    [Thu Feb 10 12:59:07 2022] cifs_umount+0xce/0xe0 [cifs]
    [Thu Feb 10 12:59:07 2022] cifs_kill_sb+0xc8/0xe0 [cifs]
    [Thu Feb 10 12:59:07 2022] deactivate_locked_super+0x5d/0xd0
    [Thu Feb 10 12:59:07 2022] cifs_smb3_do_mount+0xab9/0xbe0 [cifs]
    [Thu Feb 10 12:59:07 2022] smb3_get_tree+0x1a0/0x2e0 [cifs]
    [Thu Feb 10 12:59:07 2022] vfs_get_tree+0x52/0x140
    [Thu Feb 10 12:59:07 2022] path_mount+0x635/0x10c0
    [Thu Feb 10 12:59:07 2022] __x64_sys_mount+0x1bf/0x210
    [Thu Feb 10 12:59:07 2022] do_syscall_64+0x5c/0xc0
    [Thu Feb 10 12:59:07 2022] entry_SYSCALL_64_after_hwframe+0x44/0xae

    Reported-by: Shyam Prasad N <sprasad@microsoft.com>
    Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
    Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
    Signed-off-by: Steve French <stfrench@microsoft.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/cifs/cifsfs.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
    index 9fa930dfd78d6..21bf82fc22783 100644
    --- a/fs/cifs/cifsfs.c
    +++ b/fs/cifs/cifsfs.c
    @@ -909,6 +909,7 @@ cifs_smb3_do_mount(struct file_system_type *fs_type,

    out_super:
    deactivate_locked_super(sb);
    + return root;
    out:
    if (cifs_sb) {
    kfree(cifs_sb->prepath);
    --
    2.34.1


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