UBUNTU-CVE-2024-47679
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) ->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. [1]: https://lore.kernel.org/linux-btrfs/[email protected]/ [2]: The reason might be 1. SB_ACTIVE was removed or 2. mapping_shrinkable() return false when I reproduced the bug.
02 / AFFECTED SOFTWARE
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03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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) ->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. [1]: https://lore.kernel.org/linux-btrfs/[email protected]/ [2]: The reason might be 1. SB_ACTIVE was removed or 2. mapping_shrinkable() return false when I reproduced the bug.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/88b1afbf0f6b221f6c5bb66cc80cd3b38d696687
- https://git.kernel.org/stable/c/0eed942bc65de1f93eca7bda51344290f9c573bb
- https://git.kernel.org/stable/c/0f8a5b6d0dafa4f533ac82e98f8b812073a7c9d1
- https://git.kernel.org/stable/c/3721a69403291e2514d13a7c3af50a006ea1153b
- https://git.kernel.org/stable/c/47a68c75052a660e4c37de41e321582ec9496195
- https://git.kernel.org/stable/c/540fb13120c9eab3ef203f90c00c8e69f37449d1
- https://git.kernel.org/stable/c/6c857fb12b9137fee574443385d53914356bbe11
- https://git.kernel.org/stable/c/88b1afbf0f6b221f6c5bb66cc80cd3b38d696687
- https://ubuntu.com/security/CVE-2024-47679
- https://ubuntu.com/security/notices/USN-7166-1
- https://ubuntu.com/security/notices/USN-7166-2
- https://ubuntu.com/security/notices/USN-7166-3
- https://ubuntu.com/security/notices/USN-7166-4
- https://ubuntu.com/security/notices/USN-7186-1
- https://ubuntu.com/security/notices/USN-7186-2
- https://ubuntu.com/security/notices/USN-7194-1
- https://ubuntu.com/security/notices/USN-7276-1
- https://ubuntu.com/security/notices/USN-7277-1
- https://ubuntu.com/security/notices/USN-7293-1
- https://ubuntu.com/security/notices/USN-7294-1
- https://ubuntu.com/security/notices/USN-7294-2
- https://ubuntu.com/security/notices/USN-7294-3
- https://ubuntu.com/security/notices/USN-7294-4
- https://ubuntu.com/security/notices/USN-7295-1
- https://ubuntu.com/security/notices/USN-7301-1
- https://ubuntu.com/security/notices/USN-7303-1
- https://ubuntu.com/security/notices/USN-7303-2
- https://ubuntu.com/security/notices/USN-7303-3
- https://ubuntu.com/security/notices/USN-7304-1
- https://ubuntu.com/security/notices/USN-7310-1
- https://ubuntu.com/security/notices/USN-7311-1
- https://ubuntu.com/security/notices/USN-7384-1
- https://ubuntu.com/security/notices/USN-7384-2
- https://ubuntu.com/security/notices/USN-7385-1
- https://ubuntu.com/security/notices/USN-7386-1
- https://ubuntu.com/security/notices/USN-7393-1
- https://ubuntu.com/security/notices/USN-7401-1
- https://ubuntu.com/security/notices/USN-7403-1
- https://ubuntu.com/security/notices/USN-7413-1
- https://ubuntu.com/security/notices/USN-7468-1
- https://ubuntu.com/security/notices/USN-7539-1
- https://ubuntu.com/security/notices/USN-7540-1
- https://www.cve.org/CVERecord?id=CVE-2024-47679