CVE-2026-90339
UnknownSummary
In the Linux kernel for PowerPC, a vulnerability was found in syscall handling after enabling GENERIC_ENTRY. When seccomp or ptrace intercepts a syscall and sets a return value, system_call_exception() did not handle the -1 sentinel, overwriting the set value with -ENOSYS. The fix introduces a thread flag to track explicit return value setting and prevents overwriting.
Risk Assessment
The vulnerability may cause incorrect behavior of seccomp and ptrace filters, replacing intended error codes with -ENOSYS. This could allow bypassing security restrictions or unexpected system behavior.
Recommendation
It is recommended to apply the official Linux kernel patch fixing this issue immediately, especially on PowerPC systems where seccomp or ptrace are used.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS