From acf18c56fdcb952a06650282192e3b4ca1855c5e Mon Sep 17 00:00:00 2001 From: Anand Jain Date: Sat, 24 Feb 2018 19:43:56 +0800 Subject: [PATCH] btrfs: fix null pointer deref when target device is missing The replace target device can be missing when mounted with -o degraded, but we wont allocate a missing btrfs_device to it. So check the device before accessing. BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0 IP: btrfs_destroy_dev_replace_tgtdev+0x43/0xf0 [btrfs] Call Trace: btrfs_dev_replace_cancel+0x15f/0x180 [btrfs] btrfs_ioctl+0x2216/0x2590 [btrfs] do_vfs_ioctl+0x625/0x650 SyS_ioctl+0x4e/0x80 do_syscall_64+0x5d/0x160 entry_SYSCALL64_slow_path+0x25/0x25 This patch has been moved in front of patch "btrfs: log, when replace, is canceled by the user" that could reproduce the crash if the system reboots inside btrfs_dev_replace_start before the btrfs_dev_replace_finishing call. $ mkfs /dev/sda $ mount /dev/sda mnt $ btrfs replace start /dev/sda /dev/sdb $ mount po degraded /dev/sdb mnt Signed-off-by: Anand Jain [ added reproducer description from mail ] Signed-off-by: David Sterba --- fs/btrfs/dev-replace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c index dd717e204b5e..c523478b3de2 100644 --- a/fs/btrfs/dev-replace.c +++ b/fs/btrfs/dev-replace.c @@ -312,7 +312,7 @@ void btrfs_after_dev_replace_commit(struct btrfs_fs_info *fs_info) static char* btrfs_dev_name(struct btrfs_device *device) { - if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) + if (!device || test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) return ""; else return rcu_str_deref(device->name); -- 2.30.2