linux-kernel - Re: [PATCH v2] fs/btrfs: avoid null pointer dereference if reloc control has not been initialized

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Message-ID: <20210105113810.GL6430@suse.cz>
Date:   Tue, 5 Jan 2021 12:38:10 +0100
From:   David Sterba <dsterba@...e.cz>
To:     bodefang <bodefang@....com>
Cc:     clm@...com, josef@...icpanda.com, dsterba@...e.com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fs/btrfs: avoid null pointer dereference if reloc
 control has not been initialized

I'm keeping the rest of the mail as I received it, it's completely
garbled and would need manual reformatting. The changelog and even the
diff are completely on one line(!).

On Tue, Jan 05, 2021 at 11:08:42AM +0800, bodefang wrote:
> Similar to commmit<389305b2aa68>（“btrfs: relocation: Only remove reloc rb_trees if reloc control has been initialized”).it turns out that fs_info::reloc_ctl can be NULL in btrfs_recover_relocation() as we allocate relocation control after allreloc roots have been verified.,so there should be a check for rc to prevent null pointer dereference.
> 
> Signed-off-by: Defang Bo <bodefang@....com>Reviewed-by: David Sterba <dsterba@...e.cz>---

Oh and don't add reviewed-by unless it's explicitly stated by the
person.

> Changes since v1:
> - More accurate description for this patch to describe how the NULL can get there.
> ---
> --- fs/btrfs/relocation.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c index 3602806..ca03571 100644 --- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -626,6 +626,9 @@ static int __must_check __add_reloc_root(struct btrfs_root *root) struct mapping_node *node; struct reloc_control *rc = fs_info->reloc_ctl; + if (!rc) + return 0; + node = kmalloc(sizeof(*node), GFP_NOFS); if (!node) return -ENOMEM; @@ -703,6 +706,9 @@ static int __update_reloc_root(struct btrfs_root *root) struct rb_node *rb_node; struct mapping_node *node = NULL; struct reloc_control *rc = fs_info->reloc_ctl; + + if (!rc) + return 0; spin_lock(&rc->reloc_root_tree.lock); rb_node = rb_simple_search(&rc->reloc_root_tree.rb_root, -- 2.7.4
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> At 2021-01-04 23:11:13, "David Sterba" <dsterba@...e.cz> wrote:
> >On Sun, Dec 27, 2020 at 10:55:31PM +0800, Defang Bo wrote:
> >> Similar to commmit<389305b2>,
> >
> >Please use full commit reference like 389305b2aa68 ("btrfs: relocation:
> >Only remove reloc rb_trees if reloc control has been initialized")
> >
> >> it turns out that fs_info::reloc_ctl can be NULL ,
> >
> >Please describe how the NULL can get there.