Unknown
CVE-2024-47679
CVE-2024-47679
Description
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 bug1 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) –>evict()
// dec i_count to 0
–>iput_final()
->spin_unlock() ->evict()
Now, we have two threads simultaneously evicting
the same inode, which may trigger the BUG(inode->i_state & I_CLEAR)
statement both within clear_inode() and iput().
To fix the bug, recheck the inode->i_count after holding i_lock.
Because in the most scenarios, the first check is valid, and
the overhead of spin_lock() can be reduced.
If there is any misunderstanding, please let me know, thanks.
[2]: The reason might be 1. SB_ACTIVE was removed or 2. mapping_shrinkable()
return false when I reproduced the bug.
Add Assessment
No one has assessed this topic. Be the first to add your voice to the community.
CVSS V3 Severity and Metrics
General Information
Vendors
- linux
Products
- linux kernel
References
Miscellaneous
