[PATCH] btrfs: Defer setting new inode mode until after do_set_acl succeeds

[PATCH] btrfs: Defer setting new inode mode until after do_set_acl succeeds

[Nikolay Borisov]

Currently a reference to inode->i_mode is passed directly to
posix_acl_update_mode when setting an ACL which results in the inode's
mode always being changed. In case of errors (e.g. in do_set_acl or
even starting a transaction) the old mode needs to be re-assigned to
->i_mode. This mode recovery is done only in case do_set_acl fails,
which leads to buggy behavior in case btrfs_start_transaction fails.

Fix it by simply setting the new mode to a temporary variable which is
assigned to inode->i_mode's only when do_set_acl succeeds. This covers
both failure cases explained above.

Fixes: db0f220e98eb ("btrfs: start transaction in btrfs_set_acl")
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/acl.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
index b722866e1442..a0cfd2049ea5 100644
--- a/fs/btrfs/acl.c
+++ b/fs/btrfs/acl.c
@@ -99,7 +99,6 @@ static int do_set_acl(struct btrfs_trans_handle *trans, struct inode *inode,
 	}
 
 	ret = btrfs_setxattr(trans, inode, name, value, size, 0);
-
 out:
 	kfree(value);
 
@@ -112,12 +111,12 @@ static int do_set_acl(struct btrfs_trans_handle *trans, struct inode *inode,
 int btrfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 {
 	int ret;
-	umode_t old_mode = inode->i_mode;
+	umode_t mode;
 	struct btrfs_trans_handle *trans;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 
 	if (type == ACL_TYPE_ACCESS && acl) {
-		ret = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+		ret = posix_acl_update_mode(inode, &mode, &acl);
 		if (ret)
 			return ret;
 	}
@@ -127,9 +126,8 @@ int btrfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 		return PTR_ERR(trans);
 
 	ret = do_set_acl(trans, inode, acl, type);
-	if (ret) {
-		inode->i_mode = old_mode;
-	} else {
+	if (!ret) {
+		inode->i_mode = mode;
 		inode_inc_iversion(inode);
 		inode->i_ctime = current_time(inode);
 		set_bit(BTRFS_INODE_COPY_EVERYTHING, &BTRFS_I(inode)->runtime_flags);
-- 
2.17.1

Re: [PATCH] btrfs: Defer setting new inode mode until after do_set_acl succeeds

[Nikolay Borisov]

On 21.03.19 г. 11:27 ч., Nikolay Borisov wrote:
> Currently a reference to inode->i_mode is passed directly to
> posix_acl_update_mode when setting an ACL which results in the inode's
> mode always being changed. In case of errors (e.g. in do_set_acl or
> even starting a transaction) the old mode needs to be re-assigned to
> ->i_mode. This mode recovery is done only in case do_set_acl fails,
> which leads to buggy behavior in case btrfs_start_transaction fails.
> 
> Fix it by simply setting the new mode to a temporary variable which is
> assigned to inode->i_mode's only when do_set_acl succeeds. This covers
> both failure cases explained above.
> 
> Fixes: db0f220e98eb ("btrfs: start transaction in btrfs_set_acl")
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/acl.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)


This patch is broken and causes inconsistencies on the fs that btrfs
check detects. Test that triggers it - generic/077. I'm trying to
understand why, meanwhile this works:

diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
index b722866e1442..f56ed759e0a4 100644
--- a/fs/btrfs/acl.c
+++ b/fs/btrfs/acl.c
@@ -123,8 +123,10 @@ int btrfs_set_acl(struct inode *inode, struct
posix_acl *acl, int type)
        }

        trans = btrfs_start_transaction(root, 2);
-       if (IS_ERR(trans))
+       if (IS_ERR(trans)) {
+               inode->i_mode = old_mode;
                return PTR_ERR(trans);
+       }

        ret = do_set_acl(trans, inode, acl, type);
        if (ret) {



However it feels more like proliferating the bad style btrfs_set_acl is
structured in.

> 
> diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
> index b722866e1442..a0cfd2049ea5 100644
> --- a/fs/btrfs/acl.c
> +++ b/fs/btrfs/acl.c
> @@ -99,7 +99,6 @@ static int do_set_acl(struct btrfs_trans_handle *trans, struct inode *inode,
>  	}
>  
>  	ret = btrfs_setxattr(trans, inode, name, value, size, 0);
> -
>  out:
>  	kfree(value);
>  
> @@ -112,12 +111,12 @@ static int do_set_acl(struct btrfs_trans_handle *trans, struct inode *inode,
>  int btrfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  {
>  	int ret;
> -	umode_t old_mode = inode->i_mode;
> +	umode_t mode;
>  	struct btrfs_trans_handle *trans;
>  	struct btrfs_root *root = BTRFS_I(inode)->root;
>  
>  	if (type == ACL_TYPE_ACCESS && acl) {
> -		ret = posix_acl_update_mode(inode, &inode->i_mode, &acl);
> +		ret = posix_acl_update_mode(inode, &mode, &acl);
>  		if (ret)
>  			return ret;
>  	}
> @@ -127,9 +126,8 @@ int btrfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  		return PTR_ERR(trans);
>  
>  	ret = do_set_acl(trans, inode, acl, type);
> -	if (ret) {
> -		inode->i_mode = old_mode;
> -	} else {
> +	if (!ret) {
> +		inode->i_mode = mode;
>  		inode_inc_iversion(inode);
>  		inode->i_ctime = current_time(inode);
>  		set_bit(BTRFS_INODE_COPY_EVERYTHING, &BTRFS_I(inode)->runtime_flags);
> 

Re: [PATCH] btrfs: Defer setting new inode mode until after do_set_acl succeeds

[Johannes Thumshirn]

On 21/03/2019 10:27, Nikolay Borisov wrote:
[...]

> index b722866e1442..a0cfd2049ea5 100644
> --- a/fs/btrfs/acl.c
> +++ b/fs/btrfs/acl.c
> @@ -99,7 +99,6 @@ static int do_set_acl(struct btrfs_trans_handle *trans, struct inode *inode,
>  	}
>  
>  	ret = btrfs_setxattr(trans, inode, name, value, size, 0);
> -

Nit: unrelated change

Looks good,
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>

-- 
Johannes Thumshirn                            SUSE Labs Filesystems
jthumshirn@suse.de                                +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850

Re: [PATCH] btrfs: Defer setting new inode mode until after do_set_acl succeeds

[Johannes Thumshirn]

On 21/03/2019 13:42, Nikolay Borisov wrote:
> This patch is broken and causes inconsistencies on the fs that btrfs
> check detects. Test that triggers it - generic/077. I'm trying to
> understand why, meanwhile this works:

If you find the root cause, could you share it please?

-- 
Johannes Thumshirn                            SUSE Labs Filesystems
jthumshirn@suse.de                                +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850

Re: [PATCH] btrfs: Defer setting new inode mode until after do_set_acl succeeds

[David Sterba]

On Thu, Mar 21, 2019 at 11:27:03AM +0200, Nikolay Borisov wrote:
> Currently a reference to inode->i_mode is passed directly to
> posix_acl_update_mode when setting an ACL which results in the inode's
> mode always being changed. In case of errors (e.g. in do_set_acl or
> even starting a transaction) the old mode needs to be re-assigned to
> ->i_mode. This mode recovery is done only in case do_set_acl fails,
> which leads to buggy behavior in case btrfs_start_transaction fails.
> 
> Fix it by simply setting the new mode to a temporary variable which is
> assigned to inode->i_mode's only when do_set_acl succeeds. This covers
> both failure cases explained above.
> 
> Fixes: db0f220e98eb ("btrfs: start transaction in btrfs_set_acl")
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/acl.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
> index b722866e1442..a0cfd2049ea5 100644
> --- a/fs/btrfs/acl.c
> +++ b/fs/btrfs/acl.c
> @@ -99,7 +99,6 @@ static int do_set_acl(struct btrfs_trans_handle *trans, struct inode *inode,
>  	}
>  
>  	ret = btrfs_setxattr(trans, inode, name, value, size, 0);
> -
>  out:
>  	kfree(value);
>  
> @@ -112,12 +111,12 @@ static int do_set_acl(struct btrfs_trans_handle *trans, struct inode *inode,
>  int btrfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  {
>  	int ret;
> -	umode_t old_mode = inode->i_mode;
> +	umode_t mode;
>  	struct btrfs_trans_handle *trans;
>  	struct btrfs_root *root = BTRFS_I(inode)->root;
>  
>  	if (type == ACL_TYPE_ACCESS && acl) {
> -		ret = posix_acl_update_mode(inode, &inode->i_mode, &acl);
> +		ret = posix_acl_update_mode(inode, &mode, &acl);
>  		if (ret)
>  			return ret;
>  	}
> @@ -127,9 +126,8 @@ int btrfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  		return PTR_ERR(trans);
>  
>  	ret = do_set_acl(trans, inode, acl, type);
> -	if (ret) {
> -		inode->i_mode = old_mode;
> -	} else {
> +	if (!ret) {
> +		inode->i_mode = mode;

I like this flow much better, ie. update i_mod only if it's correct,
otherwise it's a no-op. Then we don't have to revert the change on each
possible error.

The patch that causes it is still in misc-next so the hash is not stable
and we can't use it for reference. So I suggest to fold the single
i_mode after transaction to "btrfs: start transaction in btrfs_set_acl"
and your patch can rework the i_mode handling.

We'll see when you see V2 if this could work or just go with a single
patch.