CVE-2026-63988

bridge: Fix sleep in atomic context in sysfs path

5.5 MediumFix available

In the Linux kernel, the following vulnerability has been resolved:

bridge: Fix sleep in atomic context in sysfs path

Since the start of the git history, brport_store() always acquired the bridge lock. Back then this decision made sense: The bridge lock protects the STP state of the bridge and its ports and at that time the function was only used by two STP related attributes (cost and priority).

Nowadays, brport_store() processes a lot more attributes and most of them do not need the bridge lock:

Bridge flags: Only require RTNL. Read locklessly by the data path. Annotations can be added in net-next.
FDB port flushing: Only requires the FDB lock.
Multicast attributes: Only require the multicast lock.
Group forward mask: Only requires RTNL. Read locklessly by the data path. Annotations can be added in net-next.
Backup port: Only requires RTNL. Read locklessly by the data path.

This is a problem as the bridge calls dev_set_promiscuity() when certain bridge port flags change and this function can sleep since the commit cited below, resulting in a splat such as [1].

Fix this by reducing the scope of the bridge lock and only take it when processing the two STP related attributes that require it. Remove the now stale comment from br_switchdev_set_port_flag(). The SWITCHDEV_F_DEFER flag can be removed in net-next.

[1] BUG: sleeping function called from invalid context at net/core/dev_addr_lists.c:1262 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 372, name: bash preempt_count: 201, expected: 0 RCU nest depth: 0, expected: 0 5 locks held by bash/372: #0: ffff88810c51c3f0 (sb_writers#7){.+.+}-{0:0}, at: ksys_write (fs/read_write.c:740) #1: ffff888115ce9480 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter (fs/kernfs/file.c:343) #2: ffff88810b9fd330 (kn->active#37){.+.+}-{0:0}, at: kernfs_fop_write_iter (fs/kernfs/file.c:80 fs/kernfs/file.c:344) #3: ffffffffa59473a0 (rtnl_mutex){+.+.}-{4:4}, at: brport_store (net/bridge/br_sysfs_if.c:326) #4: ffff8881099d2d58 (&br->lock){+...}-{3:3}, at: brport_store (./include/linux/spinlock.h:348 net/bridge/br_sysfs_if.c:345) Preemption disabled at: 0x0 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 Call Trace: <TASK> dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120) __might_resched.cold (kernel/sched/core.c:9163) netif_rx_mode_run (net/core/dev_addr_lists.c:1262) netif_rx_mode_sync (net/core/dev_addr_lists.c:1428) dev_set_promiscuity (net/core/dev_api.c:289) br_manage_promisc (net/bridge/br_if.c:135 net/bridge/br_if.c:172) br_port_flags_change (net/bridge/br_if.c:242 net/bridge/br_if.c:747) store_learning (net/bridge/br_sysfs_if.c:79 net/bridge/br_sysfs_if.c:235) brport_store (net/bridge/br_sysfs_if.c:346) kernfs_fop_write_iter (fs/kernfs/file.c:352) new_sync_write (fs/read_write.c:595) vfs_write (fs/read_write.c:688) ksys_write (fs/read_write.c:740) do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)

Attack profile

How easy it is to exploit

Attack vector: Local
Complexity: Low
Privileges needed: Low
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: None
Availability: High

Exploit likelihood

0.12%Unchanged since Jul 20, 2026

What each source reports

NVD Score used 5.5

In the Linux kernel, the following vulnerability has been resolved:

bridge: Fix sleep in atomic context in sysfs path

Nowadays, brport_store() processes a lot more attributes and most of them do not need the bridge lock:

Bridge flags: Only require RTNL. Read locklessly by the data path. Annotations can be added in net-next.
FDB port flushing: Only requires the FDB lock.
Multicast attributes: Only require the multicast lock.
Group forward mask: Only requires RTNL. Read locklessly by the data path. Annotations can be added in net-next.
Backup port: Only requires RTNL. Read locklessly by the data path.

This is a problem as the bridge calls dev_set_promiscuity() when certain bridge port flags change and this function can sleep since the commit cited below, resulting in a splat such as [1].

Record: CVE-2026-63988
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-667
Updated: 2026-11-02

CVE List No score

bridge: Fix sleep in atomic context in sysfs path

In the Linux kernel, the following vulnerability has been resolved:

bridge: Fix sleep in atomic context in sysfs path

Nowadays, brport_store() processes a lot more attributes and most of them do not need the bridge lock:

Bridge flags: Only require RTNL. Read locklessly by the data path. Annotations can be added in net-next.
FDB port flushing: Only requires the FDB lock.
Multicast attributes: Only require the multicast lock.
Group forward mask: Only requires RTNL. Read locklessly by the data path. Annotations can be added in net-next.
Backup port: Only requires RTNL. Read locklessly by the data path.

This is a problem as the bridge calls dev_set_promiscuity() when certain bridge port flags change and this function can sleep since the commit cited below, resulting in a splat such as [1].

Record: CVE-2026-63988
Updated: 2026-11-02

EUVDEUVD-2026-45561 No score

In the Linux kernel, the following vulnerability has been resolved:

bridge: Fix sleep in atomic context in sysfs path

Nowadays, brport_store() processes a lot more attributes and most of them do not need the bridge lock:

Bridge flags: Only require RTNL. Read locklessly by the data path. Annotations can be added in net-next.
FDB port flushing: Only requires the FDB lock.
Multicast attributes: Only require the multicast lock.
Group forward mask: Only requires RTNL. Read locklessly by the data path. Annotations can be added in net-next.
Backup port: Only requires RTNL. Read locklessly by the data path.

This is a problem as the bridge calls dev_set_promiscuity() when certain bridge port flags change and this function can sleep since the commit cited below, resulting in a splat such as [1].

Record: EUVD-2026-45561
Updated: 2026-11-02

GitHub AdvisoriesGHSA-qqj9-pc4p-85gc 5.5

In the Linux kernel, the following vulnerability has been resolved: bridge: Fix sleep in atomic...

In the Linux kernel, the following vulnerability has been resolved:

bridge: Fix sleep in atomic context in sysfs path

Nowadays, brport_store() processes a lot more attributes and most of them do not need the bridge lock:

Bridge flags: Only require RTNL. Read locklessly by the data path. Annotations can be added in net-next.
FDB port flushing: Only requires the FDB lock.
Multicast attributes: Only require the multicast lock.
Group forward mask: Only requires RTNL. Read locklessly by the data path. Annotations can be added in net-next.
Backup port: Only requires RTNL. Read locklessly by the data path.

This is a problem as the bridge calls dev_set_promiscuity() when certain bridge port flags change and this function can sleep since the commit cited below, resulting in a splat such as [1].

Record: GHSA-qqj9-pc4p-85gc
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-667
Updated: 2026-11-02

OSVBELL-CVE-2026-63988 5.5

Record: BELL-CVE-2026-63988
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVDEBIAN-CVE-2026-63988 5.5

In the Linux kernel, the following vulnerability has been resolved: bridge: Fix sleep in atomic context in sysfs path Since the start of the git history, brport_store() always acquired the bridge lock. Back then this decision made sense: The bridge lock protects the STP state of the bridge and its ports and at that time the function was only used by two STP related attributes (cost and priority). Nowadays, brport_store() processes a lot more attributes and most of them do not need the bridge lock: * Bridge flags: Only require RTNL. Read locklessly by the data path. Annotations can be added in net-next. * FDB port flushing: Only requires the FDB lock. * Multicast attributes: Only require the multicast lock. * Group forward mask: Only requires RTNL. Read locklessly by the data path. Annotations can be added in net-next. * Backup port: Only requires RTNL. Read locklessly by the data path. This is a problem as the bridge calls dev_set_promiscuity() when certain bridge port flags change and this function can sleep since the commit cited below, resulting in a splat such as [1]. Fix this by reducing the scope of the bridge lock and only take it when processing the two STP related attributes that require it. Remove the now stale comment from br_switchdev_set_port_flag(). The SWITCHDEV_F_DEFER flag can be removed in net-next. [1] BUG: sleeping function called from invalid context at net/core/dev_addr_lists.c:1262 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 372, name: bash preempt_count: 201, expected: 0 RCU nest depth: 0, expected: 0 5 locks held by bash/372: #0: ffff88810c51c3f0 (sb_writers#7){.+.+}-{0:0}, at: ksys_write (fs/read_write.c:740) #1: ffff888115ce9480 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter (fs/kernfs/file.c:343) #2: ffff88810b9fd330 (kn->active#37){.+.+}-{0:0}, at: kernfs_fop_write_iter (fs/kernfs/file.c:80 fs/kernfs/file.c:344) #3: ffffffffa59473a0 (rtnl_mutex){+.+.}-{4:4}, at: brport_store (net/bridge/br_sysfs_if.c:326) #4: ffff8881099d2d58 (&br->lock){+...}-{3:3}, at: brport_store (./include/linux/spinlock.h:348 net/bridge/br_sysfs_if.c:345) Preemption disabled at: 0x0 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 Call Trace: <TASK> dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120) __might_resched.cold (kernel/sched/core.c:9163) netif_rx_mode_run (net/core/dev_addr_lists.c:1262) netif_rx_mode_sync (net/core/dev_addr_lists.c:1428) dev_set_promiscuity (net/core/dev_api.c:289) br_manage_promisc (net/bridge/br_if.c:135 net/bridge/br_if.c:172) br_port_flags_change (net/bridge/br_if.c:242 net/bridge/br_if.c:747) store_learning (net/bridge/br_sysfs_if.c:79 net/bridge/br_sysfs_if.c:235) brport_store (net/bridge/br_sysfs_if.c:346) kernfs_fop_write_iter (fs/kernfs/file.c:352) new_sync_write (fs/read_write.c:595) vfs_write (fs/read_write.c:688) ksys_write (fs/read_write.c:740) do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)

Record: DEBIAN-CVE-2026-63988
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

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OSVUBUNTU-CVE-2026-63988 6.8

Record: UBUNTU-CVE-2026-63988
CVSS 4.0: 6.8 MediumCVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-06

OSV No score

bridge: Fix sleep in atomic context in sysfs path

In the Linux kernel, the following vulnerability has been resolved:

bridge: Fix sleep in atomic context in sysfs path

Nowadays, brport_store() processes a lot more attributes and most of them do not need the bridge lock:

Bridge flags: Only require RTNL. Read locklessly by the data path. Annotations can be added in net-next.
FDB port flushing: Only requires the FDB lock.
Multicast attributes: Only require the multicast lock.
Group forward mask: Only requires RTNL. Read locklessly by the data path. Annotations can be added in net-next.
Backup port: Only requires RTNL. Read locklessly by the data path.

This is a problem as the bridge calls dev_set_promiscuity() when certain bridge port flags change and this function can sleep since the commit cited below, resulting in a splat such as [1].

Record: CVE-2026-63988
Updated: 2026-11-02

OSVUSN-8593-1 No score

linux-ibm, linux-oracle vulnerabilities

It was discovered that some AMD Zen 2 processors did not properly isolate shared resources in the operation cache. A local attacker could possibly use this issue to corrupt instructions executed at a higher privilege level, resulting in privilege escalation. (CVE-2025-54518)