Ubuntu: (Multiple Advisories) (CVE-2025-38493): Linux kernel vulnerabilities

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

tracing/osnoise: Fix crash in timerlat_dump_stack()

We have observed kernel panics when using timerlat with stack saving,
with the following dmesg output:

memcpy: detected buffer overflow: 88 byte write of buffer size 0
WARNING: CPU: 2 PID: 8153 at lib/string_helpers.c:1032 __fortify_report+0x55/0xa0
CPU: 2 UID: 0 PID: 8153 Comm: timerlatu/2 Kdump: loaded Not tainted 6.15.3-200.fc42.x86_64 #1 PREEMPT(lazy)
Call Trace:
<TASK>
? trace_buffer_lock_reserve+0x2a/0x60
__fortify_panic+0xd/0xf
__timerlat_dump_stack.cold+0xd/0xd
timerlat_dump_stack.part.0+0x47/0x80
timerlat_fd_read+0x36d/0x390
vfs_read+0xe2/0x390
? syscall_exit_to_user_mode+0x1d5/0x210
ksys_read+0x73/0xe0
do_syscall_64+0x7b/0x160
? exc_page_fault+0x7e/0x1a0
entry_SYSCALL_64_after_hwframe+0x76/0x7e

__timerlat_dump_stack() constructs the ftrace stack entry like this:

struct stack_entry *entry;
...
memcpy(&entry->caller, fstack->calls, size);
entry->size = fstack->nr_entries;

Since commit e7186af7fb26 ("tracing: Add back FORTIFY_SOURCE logic to
kernel_stack event structure"), struct stack_entry marks its caller
field with __counted_by(size). At the time of the memcpy, entry->size
contains garbage from the ringbuffer, which under some circumstances is
zero, triggering a kernel panic by buffer overflow.

Populate the size field before the memcpy so that the out-of-bounds
check knows the correct size. This is analogous to
__ftrace_trace_stack().