perf/core: Fix refcount bug and potential UAF in perf_mmap
Syzkaller reported a refcount_t: addition on 0; use-after-free warning
in perf_mmap.
The issue is caused by a race condition between a failing mmap() setup
and a concurrent mmap() on a dependent event (e.g., using output
redirection).
In perf_mmap(), the ring_buffer (rb) is allocated and assigned to
event->rb with the mmap_mutex held. The mutex is then released to
perform map_range().
If map_range() fails, perf_mmap_close() is called to clean up.
However, since the mutex was dropped, another thread attaching to
this event (via inherited events or output redirection) can acquire
the mutex, observe the valid event->rb pointer, and attempt to
increment its reference count. If the cleanup path has already
dropped the reference count to zero, this results in a
use-after-free or refcount saturation warning.
Fix this by extending the scope of mmap_mutex to cover the
map_range() call. This ensures that the ring buffer initialization
and mapping (or cleanup on failure) happens atomically effectively,
preventing other threads from accessing a half-initialized or
dying ring buffer.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||
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| Linux | Linux | unaffected |
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| Linux | Linux | affected |
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| Vendors | Products |
|---|---|
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Linux
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Linux Kernel
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Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
Wed, 18 Mar 2026 10:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: perf/core: Fix refcount bug and potential UAF in perf_mmap Syzkaller reported a refcount_t: addition on 0; use-after-free warning in perf_mmap. The issue is caused by a race condition between a failing mmap() setup and a concurrent mmap() on a dependent event (e.g., using output redirection). In perf_mmap(), the ring_buffer (rb) is allocated and assigned to event->rb with the mmap_mutex held. The mutex is then released to perform map_range(). If map_range() fails, perf_mmap_close() is called to clean up. However, since the mutex was dropped, another thread attaching to this event (via inherited events or output redirection) can acquire the mutex, observe the valid event->rb pointer, and attempt to increment its reference count. If the cleanup path has already dropped the reference count to zero, this results in a use-after-free or refcount saturation warning. Fix this by extending the scope of mmap_mutex to cover the map_range() call. This ensures that the ring buffer initialization and mapping (or cleanup on failure) happens atomically effectively, preventing other threads from accessing a half-initialized or dying ring buffer. | |
| Title | perf/core: Fix refcount bug and potential UAF in perf_mmap | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-03-18T10:05:10.070Z
Reserved: 2026-01-13T15:37:45.989Z
Link: CVE-2026-23248
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-03-18T11:16:16.863
Modified: 2026-03-18T11:16:16.863
Link: CVE-2026-23248
Redhat
No data.
OpenCVE Enrichment
Updated: 2026-03-18T12:12:44Z
No weakness.