在 2022/4/13 21:42, chenxiaosong (A) 写道:
在 2022/4/13 20:07, Lyu Tao 写道:
Hi Xiaosong,
Thanks for keeping focusing on this bug.
I applied this CVE for the NULL dereference bug at
nfs4_valid_open_stateid() and added the following description to this
CVE due to the NFS maintainers replied that to me.
"An issue was discovered in fs/nfs/dir.c in the Linux kernel before
5.16.5. If an application sets the O_DIRECTORY flag, and tries to open
a regular file, nfs_atomic_open() performs a regular lookup. If a
regular file is found, ENOTDIR should occur, but the server instead
returns uninitialized data in the file descriptor.
Actually I'm still confused with the root cause of this bug. In the
original PoC, there is no O_DIRECTORY flag but commit ac795161c936
mentioned.
Moreover, in your latest commit ab0fc21bc710, it said "After secondly
opening a file with O_ACCMODE|O_DIRECT flags,
nfs4_valid_open_stateid() will dereference NULL nfs4_state when
lseek()." However, the original PoC opens the file only with
O_RDWR|O_CREAT for the first time.
Original PoC:
fd = openat("./file1", o_RDWR|O_CREAT, 000);
open("./file1",
O_ACCMODE|O_CREAT|O_DIRECT|O_LARGEFILE|O_NOFOLLOW|O_NOATIME|O_CLOEXEC|FASYNC|0xb3000008,
001);
lseek(fd, 9, SEEK_HOLE);
I'll update this CVE's description after I figure out these.
Best Regards,
Tao
Hi Tao:
Yes, O_ACCEMODE is _not_ necessary when fistly open() file.
When open() the file secondly, O_ACCEMODE is necessary if we want to
reproduce the bug.
Waiting for your modification of the CVE's description.
Best Regards.
.
My reproducer:
1. mount -t nfs -o vers=4.2 $server_ip:/ /mnt/
2. fd = open("/mnt/file", O_ACCMODE|O_DIRECT|O_CREAT)
3. close(fd)
4. fd = open("/mnt/file", O_ACCMODE|O_DIRECT)
5. lseek(fd)
When firstly open() file, O_ACCMODE|O_DIRECT is _not_ necessary, we just
use O_CREAT to create new file.
When secondly open() file, only O_ACCMODE|O_DIRECT is necessary,
O_CREAT|O_LARGEFILE|O_NOFOLLOW|O_NOATIME|O_CLOEXEC|FASYNC|0xb3000008 in
your original PoC is not necessary (however, they are harmless).
