CVE-2026-90339 powerpc/syscall: Fix syscall skip handling for seccomp and ptrace
A flaw in the Linux kernel PowerPC syscall handling allows bypassing seccomp or ptrace restrictions, potentially enabling unauthorized system call execution.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90339?
CVE-2026-90339 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
powerpc/syscall: Fix syscall skip handling for seccomp and ptrace
After enabling GENERIC_ENTRY on PowerPC, syscall_enter_from_user_mode() returns -1 as a sentinel to signal that seccomp or ptrace has intercepted the syscall and already set a return value via syscall_set_return_value(). system_call_exception() was not handling this sentinel, and since -1UL is >= NR_syscalls, the code fell into the out-of-range path and returned -ENOSYS, overwriting the errno already placed in regs->gpr[3].
The naive fix of checking r0 == -1L before the NR_syscalls bounds check is ambiguous: a user legitimately calling syscall(-1) also produces r0 == -1L, and a tracer intercepting such a call would have its injected return value silently discarded.
Fix this by introducing a thread flag that is set whenever syscall_set_return_value() explicitly updates the return value. In system_call_exception(), check and clear this flag before dispatching the syscall, and return the preset value directly when it is present. This ensures that an explicitly supplied return value always suppresses syscall execution, regardless of the syscall number.
This handles all seccomp actions correctly:
- SECCOMP_RET_ERRNO, SECCOMP_RET_TRACE (no tracer), SECCOMP_RET_USER_NOTIF: all call syscall_set_return_value(), flag is set, injected value returned. - SECCOMP_RET_TRAP, SECCOMP_RET_KILL: call syscall_rollback() and deliver a signal; flag is not set, but the process is dying so the return value is irrelevant.
The fix covers both ppc32 and ppc64 with no #ifdefs.
Which versions are affected by CVE-2026-90339?
How do I fix CVE-2026-90339?
Apply the vendor's patch.
Is CVE-2026-90339 being exploited?
There is no known exploitation of CVE-2026-90339 in the wild and no public exploit code.
Sources
Also known as GHSA-qfw2-5x2v-5xgv, UBUNTU-CVE-2026-90339.