In the Linux kernel, the following vulnerability has been resolved:
tracing: Have trace_event_file have ref counters
The following can crash the kernel:
The above commands:
The above causes a crash!
BUG: kernel NULL pointer dereference, address: 0000000000000028
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 6 PID: 877 Comm: bash Not tainted 6.5.0-rc4-test-00008-g2c6b6b1029d4-dirty #186
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:tracing_release_file_tr+0xc/0x50
What happens here is that the kprobe event creates a trace_event_file
“file” descriptor that represents the file in tracefs to the event. It
maintains state of the event (is it enabled for the given instance?).
Opening the “enable” file gets a reference to the event “file” descriptor
via the open file descriptor. When the kprobe event is deleted, the file is
also deleted from the tracefs system which also frees the event “file”
descriptor.
But as the tracefs file is still opened by user space, it will not be
totally removed until the final dput() is called on it. But this is not
true with the event “file” descriptor that is already freed. If the user
does a write to or simply closes the file descriptor it will reference the
event “file” descriptor that was just freed, causing a use-after-free bug.
To solve this, add a ref count to the event “file” descriptor as well as a
new flag called “FREED”. The “file” will not be freed until the last
reference is released. But the FREE flag will be set when the event is
removed to prevent any more modifications to that event from happening,
even if there’s still a reference to the event “file” descriptor.
git.kernel.org/stable/c/2c9de867ca285c397cd71af703763fe416265706
git.kernel.org/stable/c/2fa74d29fc1899c237d51bf9a6e132ea5c488976
git.kernel.org/stable/c/9034c87d61be8cff989017740a91701ac8195a1d
git.kernel.org/stable/c/961c4511c7578d6b8f39118be919016ec3db1c1e
git.kernel.org/stable/c/a98172e36e5f1b3d29ad71fade2d611cfcc2fe6f
git.kernel.org/stable/c/bb32500fb9b78215e4ef6ee8b4345c5f5d7eafb4
git.kernel.org/stable/c/cbc7c29dff0fa18162f2a3889d82eeefd67305e0