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 10 days 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 10 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 10 days ago·verify at source
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