On Mon, Mar 18, 2019 at 10:48:19AM +0800, Qu Wenruo wrote:
> Commit 514e70150b60 ("btrfs: relocation: Delay reloc tree deletion after
> merge_reloc_roots()") expands the life span of root->reloc_root.
Commit 514e70150b60 does not exist in linus.git, by the subject it's
d2311e69857815a .
> This breaks certain check on fs_info->reloc_ctl.
> Before that commit, if we have a root with valid reloc_root, then it's
> ensured to have fs_info->reloc_ctl.
>
> But now since reloc_root doesn't always mean a valid fs_info->reloc_ctl,
> such check is unreliable and can cause the following NULL pointer
> dereference:
> BUG: unable to handle kernel NULL pointer dereference at 00000000000005c1
> IP: btrfs_reloc_pre_snapshot+0x20/0x50 [btrfs]
> PGD 0 P4D 0
> Oops: 0000 [#1] SMP PTI
> CPU: 0 PID: 10379 Comm: snapperd Not tainted 4.12.14-lp150.12.53-default #1 openSUSE Leap 15.0
This is probably a backport to 4.12, the patch that caused that has been
merged to master recently. I wonder if this can also be triggered on
unpatched mainline, ie. if we're missing a test for that.
I'll fix the commit and add it to misc-next, thanks.
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
> Call Trace:
> create_pending_snapshot+0xd7/0xfc0 [btrfs]
> create_pending_snapshots+0x8e/0xb0 [btrfs]
> btrfs_commit_transaction+0x2ac/0x8f0 [btrfs]
> btrfs_mksubvol+0x561/0x570 [btrfs]
> btrfs_ioctl_snap_create_transid+0x189/0x190 [btrfs]
> btrfs_ioctl_snap_create_v2+0x102/0x150 [btrfs]
> btrfs_ioctl+0x5c9/0x1e60 [btrfs]
> do_vfs_ioctl+0x90/0x5f0
> SyS_ioctl+0x74/0x80
> do_syscall_64+0x7b/0x150
> entry_SYSCALL_64_after_hwframe+0x3d/0xa2
> RIP: 0033:0x7fd7cdab8467
>
> Fix it by explicitly checking fs_info->reloc_ctl other than using the
> implied root->reloc_root.
>
> Fixes: 514e70150b60 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots()")
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> fs/btrfs/relocation.c | 12 +++++-------
> 1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index ddf028509931..351fa506dc9b 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -4667,14 +4667,12 @@ int btrfs_reloc_cow_block(struct btrfs_trans_handle *trans,
> void btrfs_reloc_pre_snapshot(struct btrfs_pending_snapshot *pending,
> u64 *bytes_to_reserve)
> {
> - struct btrfs_root *root;
> - struct reloc_control *rc;
> + struct btrfs_root *root = pending->root;
> + struct reloc_control *rc = root->fs_info->reloc_ctl;
>
> - root = pending->root;
> - if (!root->reloc_root)
> + if (!root->reloc_root || !rc)
> return;
>
> - rc = root->fs_info->reloc_ctl;
> if (!rc->merge_reloc_tree)
> return;
>
> @@ -4703,10 +4701,10 @@ int btrfs_reloc_post_snapshot(struct btrfs_trans_handle *trans,
> struct btrfs_root *root = pending->root;
> struct btrfs_root *reloc_root;
> struct btrfs_root *new_root;
> - struct reloc_control *rc;
> + struct reloc_control *rc = root->fs_info->reloc_ctl;
> int ret;
>
> - if (!root->reloc_root)
> + if (!root->reloc_root || !rc)
> return 0;
>
> rc = root->fs_info->reloc_ctl;
> --
> 2.21.0
