CVE-2026-52939: net/rds: fix NULL deref in rds_ib_send_cqe_handler() on masked atomic completion
In the Linux kernel, the following vulnerability has been resolved:
net/rds: fix NULL deref in rdsibsendcqehandler() on masked atomic completion
rdsibxmitatomic() always programs a masked atomic opcode (IBWRMASKEDATOMICCMPANDSWP or IBWRMASKEDATOMICFETCHANDADD) for every RDS atomic cmsg. But the completion-side switch in rdsibsendunmapop() only handles the non-masked opcodes, so a masked atomic completion falls through to default and returns rm == NULL while send->sop is left set. rdsibsendcqehandler() then dereferences the NULL rm via rm->mfinalop, oopsing in softirq context. An unprivileged AFRDS sendmsg() of an atomic cmsg over an active RDS/IB connection triggers it; on hardware that natively accepts masked atomics (mlx4, mlx5) no extra setup is needed.
RDS/IB: rdsibsendunmapop: unexpected opcode 0xd in WR! Oops: general protection fault [#1] SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000190-0x0000000000000197] RIP: rdsibsendcqehandler+0x25c/0xb10 (net/rds/ibsend.c:282) Call Trace: <IRQ> rdsibsendcqehandler (net/rds/ibsend.c:282) pollscq (net/rds/ibcm.c:274) rdsibtaskletfnsend (net/rds/ibcm.c:294) taskletactioncommon (kernel/softirq.c:943) handlesoftirqs (kernel/softirq.c:573) runksoftirqd (kernel/softirq.c:479) </IRQ> Kernel panic - not syncing: Fatal exception in interrupt
Handle the masked atomic opcodes in the same case as the non-masked ones: they map to the same struct rdsmessage.atomic union member, so the existing containerof()/rdsibsendunmapatomic() body is correct for them.
Affected Software
Remediation
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Event History
Frequently Asked Questions
What is the severity of CVE-2026-52939?
CVE-2026-52939 has been assigned a risk score of 62, indicating a medium-high severity level.
How do I fix CVE-2026-52939?
To fix CVE-2026-52939, update the Linux kernel to the latest patched version that addresses this vulnerability.
What impact does CVE-2026-52939 have on systems?
CVE-2026-52939 can lead to a NULL dereference in the rds_ib_send_cqe_handler(), potentially resulting in system crashes.
Which versions of the Linux kernel are affected by CVE-2026-52939?
CVE-2026-52939 affects specific versions of the Linux kernel that implement the RDS (Reliable Datagram Sockets) protocol.
Is there a workaround for CVE-2026-52939 before applying a patch?
Currently, the best resolution for CVE-2026-52939 is to apply the available kernel patch, as no reliable workaround has been provided.