Bug 2507121 (CVE-2026-64417)

Summary: CVE-2026-64417 kernel: mm: shrinker: fix NULL pointer dereference in debugfs
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: low    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's memory management (mm) shrinker subsystem. This vulnerability arises because the `shrinker_debugfs_add()` function unconditionally creates debugfs files for 'count' and 'scan' operations, even if the corresponding callback functions (like `scan_objects()`) are not implemented by a specific shrinker. 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. This can lead to a kernel panic, effectively causing a denial of service (DoS) on the system.
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Description OSIDB Bzimport 2026-07-25 10:06:09 UTC 
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:
 <TASK>
 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.
Comment 1 TEJ RATHI 2026-07-30 03:52:40 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026072533-CVE-2026-64417-50a1@gregkh/T