• Takashi Iwai's avatar
    Btrfs: Fix memory corruption by ulist_add_merge() on 32bit arch · 4eb1f66d
    Takashi Iwai authored
    We've got bug reports that btrfs crashes when quota is enabled on
    32bit kernel, typically with the Oops like below:
     BUG: unable to handle kernel NULL pointer dereference at 00000004
     IP: [<f9234590>] find_parent_nodes+0x360/0x1380 [btrfs]
     *pde = 00000000
     Oops: 0000 [#1] SMP
     CPU: 0 PID: 151 Comm: kworker/u8:2 Tainted: G S      W 3.15.2-1.gd43d97e-default #1
     Workqueue: btrfs-qgroup-rescan normal_work_helper [btrfs]
     task: f1478130 ti: f147c000 task.ti: f147c000
     EIP: 0060:[<f9234590>] EFLAGS: 00010213 CPU: 0
     EIP is at find_parent_nodes+0x360/0x1380 [btrfs]
     EAX: f147dda8 EBX: f147ddb0 ECX: 00000011 EDX: 00000000
     ESI: 00000000 EDI: f147dda4 EBP: f147ddf8 ESP: f147dd38
      DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
     CR0: 8005003b CR2: 00000004 CR3: 00bf3000 CR4: 00000690
     Stack:
      00000000 00000000 f147dda4 00000050 00000001 00000000 00000001 00000050
      00000001 00000000 d3059000 00000001 00000022 000000a8 00000000 00000000
      00000000 000000a1 00000000 00000000 00000001 00000000 00000000 11800000
     Call Trace:
      [<f923564d>] __btrfs_find_all_roots+0x9d/0xf0 [btrfs]
      [<f9237bb1>] btrfs_qgroup_rescan_worker+0x401/0x760 [btrfs]
      [<f9206148>] normal_work_helper+0xc8/0x270 [btrfs]
      [<c025e38b>] process_one_work+0x11b/0x390
      [<c025eea1>] worker_thread+0x101/0x340
      [<c026432b>] kthread+0x9b/0xb0
      [<c0712a71>] ret_from_kernel_thread+0x21/0x30
      [<c0264290>] kthread_create_on_node+0x110/0x110
    
    This indicates a NULL corruption in prefs_delayed list.  The further
    investigation and bisection pointed that the call of ulist_add_merge()
    results in the corruption.
    
    ulist_add_merge() takes u64 as aux and writes a 64bit value into
    old_aux.  The callers of this function in backref.c, however, pass a
    pointer of a pointer to old_aux.  That is, the function overwrites
    64bit value on 32bit pointer.  This caused a NULL in the adjacent
    variable, in this case, prefs_delayed.
    
    Here is a quick attempt to band-aid over this: a new function,
    ulist_add_merge_ptr() is introduced to pass/store properly a pointer
    value instead of u64.  There are still ugly void ** cast remaining
    in the callers because void ** cannot be taken implicitly.  But, it's
    safer than explicit cast to u64, anyway.
    
    Bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=887046
    Cc: <stable@vger.kernel.org> [v3.11+]
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    Signed-off-by: default avatarChris Mason <clm@fb.com>
    4eb1f66d
backref.c 48.5 KB