Overview

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

net/rds: Fix circular locking dependency in rds_tcp_tune

syzbot reported a circular locking dependency in rds_tcp_tune() where sk_net_refcnt_upgrade() is called while holding the socket lock:

====================================================== WARNING: possible circular locking dependency detected

kworker/u10:8/15040 is trying to acquire lock: ffffffff8e9aaf80 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_noprof+0x4b/0x6f0

but task is already holding lock: ffff88805a3c1ce0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: rds_tcp_tune+0xd7/0x930

The issue occurs because sk_net_refcnt_upgrade() performs memory allocation (via get_net_track() -> ref_tracker_alloc()) while the socket lock is held, creating a circular dependency with fs_reclaim.

Fix this by moving sk_net_refcnt_upgrade() outside the socket lock critical section. This is safe because the fields modified by the sk_net_refcnt_upgrade() call (sk_net_refcnt, ns_tracker) are not accessed by any concurrent code path at this point.

v2:

• Corrected fixes tag
• check patch line wrap nits
• ai commentary nits

Affected

• Linux >= 3a58f13a881ed351198ffab4cf9953cf19d2ab3a < ce5be6703afd2ac2ff7dabd397137d71d22d4bc3
• Linux >= 3a58f13a881ed351198ffab4cf9953cf19d2ab3a < 8babb271403378ba6836f6c8599c5313d0e2355d
• Linux >= 3a58f13a881ed351198ffab4cf9953cf19d2ab3a < 8519e6883a942e510f33a0e634e27bcc3a844a40
• Linux >= 3a58f13a881ed351198ffab4cf9953cf19d2ab3a < 6ce948fa54599f369ff7fe8b793a6aae4b0762b2
• Linux >= 3a58f13a881ed351198ffab4cf9953cf19d2ab3a < 026bbaeeab9e04534ee58882b6447300629b42f6
• Linux >= 3a58f13a881ed351198ffab4cf9953cf19d2ab3a < 6a877ececd6daa002a9a0002cd0fbca6592a9244
• Linux 2a6efabed754c9dcf27e6def71317b374f58a852
• Linux >= 5.17.7 < 5.18
• Linux 5.18

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.