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Linux Kernel: Fix Memory Corruption When Creating Event Groups
CVE-2026-23127
Summary
A fix has been made to the Linux kernel to prevent memory corruption when creating event groups. This issue occurred when a group leader event was mapped into memory and then a new event was added to the group, which could cause a warning and potentially corrupt memory. Users should update their kernel to the latest version to ensure this issue is resolved.
Original title
In the Linux kernel, the following vulnerability has been resolved:
perf: Fix refcount warning on event->mmap_count increment
When calling refcount_inc(&event->mmap_count) inside perf_mmap_rb(), ...
Original description
In the Linux kernel, the following vulnerability has been resolved:
perf: Fix refcount warning on event->mmap_count increment
When calling refcount_inc(&event->mmap_count) inside perf_mmap_rb(), the
following warning is triggered:
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25
PoC:
struct perf_event_attr attr = {0};
int fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
int victim = syscall(__NR_perf_event_open, &attr, 0, -1, fd,
PERF_FLAG_FD_OUTPUT);
mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED, victim, 0);
This occurs when creating a group member event with the flag
PERF_FLAG_FD_OUTPUT. The group leader should be mmap-ed and then mmap-ing
the event triggers the warning.
Since the event has copied the output_event in perf_event_set_output(),
event->rb is set. As a result, perf_mmap_rb() calls
refcount_inc(&event->mmap_count) when event->mmap_count = 0.
Disallow the case when event->mmap_count = 0. This also prevents two
events from updating the same user_page.
perf: Fix refcount warning on event->mmap_count increment
When calling refcount_inc(&event->mmap_count) inside perf_mmap_rb(), the
following warning is triggered:
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25
PoC:
struct perf_event_attr attr = {0};
int fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
int victim = syscall(__NR_perf_event_open, &attr, 0, -1, fd,
PERF_FLAG_FD_OUTPUT);
mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED, victim, 0);
This occurs when creating a group member event with the flag
PERF_FLAG_FD_OUTPUT. The group leader should be mmap-ed and then mmap-ing
the event triggers the warning.
Since the event has copied the output_event in perf_event_set_output(),
event->rb is set. As a result, perf_mmap_rb() calls
refcount_inc(&event->mmap_count) when event->mmap_count = 0.
Disallow the case when event->mmap_count = 0. This also prevents two
events from updating the same user_page.
Published: 14 Feb 2026 · Updated: 10 Mar 2026 · First seen: 6 Mar 2026