[PATCH 3.16 136/136] fs/dcache: move security_d_instantiate() behind attaching dentry to inode

Ben Hutchings
2019-12-17T00:52:43Z

From: "zhangyi (F)" <yi.zhang@huawei.com>

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.

[ 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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/dcache.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1685,7 +1685,6 @@ void d_instantiate_new(struct dentry *en
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));
@@ -1693,6 +1692,7 @@ void d_instantiate_new(struct dentry *en
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);