Medium [CVE-2026-64417] fix NULL pointer dereference in debugfs
This medium-severity Red Hat Linux advisory covers CVE-2026-64417.
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Summary
In the Linux kernel, the following vulnerability has been resolved: mm: shrinker: fix NULL pointer dereference in debugfs shrinker_debugfs_add() creates both "count" and "scan" debugfs files unconditionally. That assumes every shrinker implements both count_objects() and scan_objects(), which is not guaranteed.
For example, the xen-backend shrinker sets count_objects() but leaves scan_objects() NULL, so writing to its scan file calls through a NULL function pointer and panics the kernel: BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: 0010:0x0 Code: Unable to access opcode bytes at 0xffffffffffffffd6.
Call Trace: shrinker_debugfs_scan_write+0x12e/0x270 full_proxy_write+0x5f/0x90 vfs_write+0xde/0x420? filp_flush+0x75/0x90? filp_close+0x1d/0x30? do_dup2+0xb8/0x120 ksys_write+0x68/0xf0? filp_flush+0x75/0x90 do_syscall_64+0xb3/0x5b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e The count path has the same issue in principle if a shrinker omits count_objects().
To fix it, only create "count" and "scan" debugfs files when the corresponding callbacks are present. A flaw was found in the Linux kernel's memory management (mm) shrinker subsystem.
A local attacker could trigger a NULL pointer dereference by attempting to write to a scan file associated with a shrinker that has a missing `scan_objects()` callback.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · medium-confidence parse· fetched 1 month ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 1 month ago·verify at source
Mitigation
The source record does not include mitigation steps. That does not mean no fix exists. Read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 1 month ago·verify at source
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