powerpc/syscall: Fix syscall skip handling for seccomp and ptrace

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Summary

CVECVE-2026-90339
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 17:17:32 UTC
Updated2026-09-17 17:17:32 UTC
DescriptionIn 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.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected bee25f97ad24641df55cb3887eb5bfcb2b9d8fbc 19b54740e2e1102c7d48553d9e0347c1f6af22b0 git Not specified
CNA Linux Linux affected bee25f97ad24641df55cb3887eb5bfcb2b9d8fbc 69cb2be898be6d5826cacd1a628f6945a24480b6 git Not specified
CNA Linux Linux affected 7.2 Not specified
CNA Linux Linux unaffected 7.2 semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/19b54740e2e1102c7d48553d9e0347c1f6af22b0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/69cb2be898be6d5826cacd1a628f6945a24480b6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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