Bug 2524484 (CVE-2026-74735)

Summary: CVE-2026-74735 kernel: l2tp: fix tunnel and session refcount leak on seq_file release
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
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 L2TP (Layer 2 Tunneling Protocol) implementation. A local user could trigger a reference count leak by closing specific `/proc` or `/sys` files related to L2TP tunnels and sessions before fully reading their content. This could lead to resource exhaustion, potentially causing a Denial of Service (DoS) condition on the system.
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Description OSIDB Bzimport 2026-08-26 14:59:40 UTC 
In the Linux kernel, the following vulnerability has been resolved:

l2tp: fix tunnel and session refcount leak on seq_file release

In pppol2tp_proc_open() and l2tp_dfs_seq_open(), iteration state
(pd->tunnel and pd->session) is kept in seq_file private data to allow
iteration across multiple read() system calls.

However, if userspace closes /proc/net/pppol2tp or /sys/kernel/debug/l2tp/tunnels
before reading to end-of-file (EOF), any tunnel or session reference stored in
pd->tunnel / pd->session is left un-dropped when seq_file private data is freed.

Fix this by dropping any remaining pd->tunnel and pd->session references in
pppol2tp_proc_release() and l2tp_dfs_seq_release() when closing the file.
Comment 1 gkamathe 2026-08-27 11:53:13 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082656-CVE-2026-74735-e7ef@gregkh/T