[PATCH] fs/btrfs: init csum_list before possible free

[PATCH] fs/btrfs: init csum_list before possible free

[Dan Robertson]

The scrub_ctx csum_list member must be initialized before
scrub_free_ctx is called. If the csum_list is not initialized
beforehand, the list_empty call in scrub_free_csums will result
in a null deref.

Signed-off-by: Dan Robertson <dan@dlrobertson.com>
---
 fs/btrfs/scrub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 6dcd36d7b849..1e08ad1fe2aa 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -584,6 +584,7 @@ static noinline_for_stack struct scrub_ctx *scrub_setup_ctx(
 	sctx->pages_per_rd_bio = SCRUB_PAGES_PER_RD_BIO;
 	sctx->curr = -1;
 	sctx->fs_info = fs_info;
+	INIT_LIST_HEAD(&sctx->csum_list);
 	for (i = 0; i < SCRUB_BIOS_PER_SCTX; ++i) {
 		struct scrub_bio *sbio;
 
@@ -608,7 +609,6 @@ static noinline_for_stack struct scrub_ctx *scrub_setup_ctx(
 	atomic_set(&sctx->workers_pending, 0);
 	atomic_set(&sctx->cancel_req, 0);
 	sctx->csum_size = btrfs_super_csum_size(fs_info->super_copy);
-	INIT_LIST_HEAD(&sctx->csum_list);
 
 	spin_lock_init(&sctx->list_lock);
 	spin_lock_init(&sctx->stat_lock);
-- 
2.20.1

Re: [PATCH] fs/btrfs: init csum_list before possible free

[Nikolay Borisov]

On 19.02.19 г. 4:56 ч., Dan Robertson wrote:
> The scrub_ctx csum_list member must be initialized before
> scrub_free_ctx is called. If the csum_list is not initialized
> beforehand, the list_empty call in scrub_free_csums will result
> in a null deref.
> 
> Signed-off-by: Dan Robertson <dan@dlrobertson.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/scrub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index 6dcd36d7b849..1e08ad1fe2aa 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -584,6 +584,7 @@ static noinline_for_stack struct scrub_ctx *scrub_setup_ctx(
>  	sctx->pages_per_rd_bio = SCRUB_PAGES_PER_RD_BIO;
>  	sctx->curr = -1;
>  	sctx->fs_info = fs_info;
> +	INIT_LIST_HEAD(&sctx->csum_list);
>  	for (i = 0; i < SCRUB_BIOS_PER_SCTX; ++i) {
>  		struct scrub_bio *sbio;
>  
> @@ -608,7 +609,6 @@ static noinline_for_stack struct scrub_ctx *scrub_setup_ctx(
>  	atomic_set(&sctx->workers_pending, 0);
>  	atomic_set(&sctx->cancel_req, 0);
>  	sctx->csum_size = btrfs_super_csum_size(fs_info->super_copy);
> -	INIT_LIST_HEAD(&sctx->csum_list);
>  
>  	spin_lock_init(&sctx->list_lock);
>  	spin_lock_init(&sctx->stat_lock);
> 

Re: [PATCH] fs/btrfs: init csum_list before possible free

[David Sterba]

On Tue, Feb 19, 2019 at 02:56:43AM +0000, Dan Robertson wrote:
> The scrub_ctx csum_list member must be initialized before
> scrub_free_ctx is called. If the csum_list is not initialized
> beforehand, the list_empty call in scrub_free_csums will result
> in a null deref.
> 
> Signed-off-by: Dan Robertson <dan@dlrobertson.com>

Reviewed-by: David Sterba <dsterba@suse.com>

Thanks, it's been there since the first merge of scrub, but hard to hit.

Re: [PATCH] fs/btrfs: init csum_list before possible free

[Dan Robertson]

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> Thanks, it's been there since the first merge of scrub, but hard to hit.

Yeah, very hard to hit. Debated submitting a patch, but the fix seemed
simple enough, so figured I'd send one in.

Side note: I noticed most of the time ENOMEM is hit in fs/btrfs BUG or BUG_ON is
called. Would it be better (more in line with the fs/btrfs style) to call BUG or
BUG_ON e.g. BUG_ON(!sbio) instead of goto nomem at fs/btrfs/scrub.c:592?

Cheers,

Dan

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Re: [PATCH] fs/btrfs: init csum_list before possible free

[David Sterba]

On Thu, Feb 21, 2019 at 02:57:27PM +0000, Dan Robertson wrote:
> > Thanks, it's been there since the first merge of scrub, but hard to hit.
> 
> Yeah, very hard to hit. Debated submitting a patch, but the fix seemed
> simple enough, so figured I'd send one in.
> 
> Side note: I noticed most of the time ENOMEM is hit in fs/btrfs BUG or BUG_ON is
> called. Would it be better (more in line with the fs/btrfs style) to call BUG or
> BUG_ON e.g. BUG_ON(!sbio) instead of goto nomem at fs/btrfs/scrub.c:592?

No, we want to get rid of the BUG_ONs as a poor substitute for error
handling. The ENOMEM case is usually a hard one to fix so you still can
see a lot of them, but there are places where it's simple enough to
rollback and return ENOMEM up to the original caller. Scrub in this case
is restartable and if scrub_setup_ctx fails, it's at the time of start
and the user is properly notified.

Re: [PATCH] fs/btrfs: init csum_list before possible free

[Dan Robertson]

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Got it. Thanks for the clarification.

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