Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

vfs: fix race between evice_inodes() and find_inode()&iput()

Hi, all

Recently I noticed a bug[1] in btrfs, after digged it into and I believe it'a race in vfs.

Let's assume there's a inode (ie ino 261) with i_count 1 is called by iput(), and there's a concurrent thread calling generic_shutdown_super().

cpu0: cpu1: iput() // i_count is 1 ->spin_lock(inode) ->dec i_count to 0 ->iput_final() generic_shutdown_super() ->__inode_add_lru() ->evict_inodes() // cause some reason[2] ->if (atomic_read(inode->i_count)) continue; // return before // inode 261 passed the above check // list_lru_add_obj() // and then schedule out ->spin_unlock() // note here: the inode 261 // was still at sb list and hash list, // and I_FREEING|I_WILL_FREE was not been set

btrfs_iget() // after some function calls ->find_inode() // found the above inode 261 ->spin_lock(inode) // check I_FREEING|I_WILL_FREE // and passed ->__iget() ->spin_unlock(inode) // schedule back ->spin_lock(inode) // check (I_NEW|I_FREEING|I_WILL_FREE) flags, // passed and set I_FREEING iput() ->spin_unlock(inode) ->spin_lock(inode)…