Re: [PATCH for linux 4.4.y/3.16.y] fs/dcache: move security_d_instantiate() behind attaching dentry to inode

[Ben Hutchings <ben@decadent.org.uk>]

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On Wed, 2019-11-06 at 17:43 +0800, zhangyi (F) wrote:
> During backport 1e2e547a93a "do d_instantiate/unlock_new_inode
> combinations safely", there was a error instantiating sequence of
> attaching dentry to inode and calling security_d_instantiate().
> 
> Before commit ce23e640133 "->getxattr(): pass dentry and inode as
> separate arguments" and b96809173e9 "security_d_instantiate(): move to
> the point prior to attaching dentry to inode", security_d_instantiate()
> should be called beind __d_instantiate(), otherwise it will trigger
> below problem when CONFIG_SECURITY_SMACK on ext4 was enabled because
> d_inode(dentry) used by ->getxattr() is NULL before __d_instantiate()
> instantiate inode.

Thanks, I've queued this up for 3.16.

Ben.

> [   31.858026] BUG: unable to handle kernel paging request at ffffffffffffff70
> ...
> [   31.882024] Call Trace:
> [   31.882378]  [<ffffffffa347f75c>] ext4_xattr_get+0x8c/0x3e0
> [   31.883195]  [<ffffffffa3489454>] ext4_xattr_security_get+0x24/0x40
> [   31.884086]  [<ffffffffa336a56b>] generic_getxattr+0x5b/0x90
> [   31.884907]  [<ffffffffa3700514>] smk_fetch+0xb4/0x150
> [   31.885634]  [<ffffffffa3700772>] smack_d_instantiate+0x1c2/0x550
> [   31.886508]  [<ffffffffa36f9a5a>] security_d_instantiate+0x3a/0x80
> [   31.887389]  [<ffffffffa3353b26>] d_instantiate_new+0x36/0x130
> [   31.888223]  [<ffffffffa342b1ef>] ext4_mkdir+0x4af/0x6a0
> [   31.888928]  [<ffffffffa3343470>] vfs_mkdir+0x100/0x280
> [   31.889536]  [<ffffffffa334b086>] SyS_mkdir+0xb6/0x170
> [   31.890255]  [<ffffffffa307c855>] ? trace_do_page_fault+0x95/0x2b0
> [   31.891134]  [<ffffffffa3c5e078>] entry_SYSCALL_64_fastpath+0x18/0x73
> 
> Cc: <stable@vger.kernel.org> # 3.16, 4.4
> Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
> ---
>  fs/dcache.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 5a1c36dc5d65..baa00718d8d1 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -1900,7 +1900,6 @@ void d_instantiate_new(struct dentry *entry, struct inode *inode)
>  	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
>  	BUG_ON(!inode);
>  	lockdep_annotate_inode_mutex_key(inode);
> -	security_d_instantiate(entry, inode);
>  	spin_lock(&inode->i_lock);
>  	__d_instantiate(entry, inode);
>  	WARN_ON(!(inode->i_state & I_NEW));
> @@ -1908,6 +1907,7 @@ void d_instantiate_new(struct dentry *entry, struct inode *inode)
>  	smp_mb();
>  	wake_up_bit(&inode->i_state, __I_NEW);
>  	spin_unlock(&inode->i_lock);
> +	security_d_instantiate(entry, inode);
>  }
>  EXPORT_SYMBOL(d_instantiate_new);
>  
-- 
Ben Hutchings
If the facts do not conform to your theory, they must be disposed of.



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