On 8/31/26 10:09 AM, Mukesh Kumar Chaurasiya wrote:
On Fri, Aug 28, 2026 at 11:08:11AM +0530, Shrikanth Hegde wrote:Shivaprasad reported a boot failure due to userspace processes crash on abort() from libc.so.6. It was bisected to merge request commit '3424d8c18a7d ("Merge tag 'core-entry-2026-08-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")' Upon checking the merge, when syscall_enter_from_user_mode_randomize_stack fails, which could happen when a tracer like seccomp or ptrace intercepts and skips the syscall, the code returns to userspace immediately without clearing the intermediate flag which was set. When the next syscall is made, it immediately aborts the valid syscall since the flag is still set. Hence clear the flag on occurrence of first failure. Reported-by: Shivaprasad G Bhat <[email protected]> Closes: https://lore.kernel.org/all/[email protected]/ Fixes: 3424d8c18a7d ("Merge tag 'core-entry-2026-08-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip") Signed-off-by: Shrikanth Hegde <[email protected]> --- PS: I have kept the block below since earlier code was checking it regardless of result of syscall_enter_from_user_mode. If it turns out to be a redundant, it can be removed later.I think it is redundant as of now. The TIF_SYSCALL_RET flag is set when error is set by the ptrace or seccomp, If the error value is set then the syscall_enter_from_user_mode_randomize_stack will return false. Hence the next check will become redundant. I also see that TIF_SYSCALL_RET is also set when processing the ptrace syscall, Which can leave the flag set for next syscall execution. Which can again trigger the same issue.
I believe it is a pre-existing bug which can be fixed independent of this issue. Since merge request broke the userspace it is better we fix it right away and this pre-existing issue fix can be done subsequently. No?
Regards, Mukesharch/powerpc/kernel/syscall.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c index 4916c205c4bb..fbefe1927b10 100644 --- a/arch/powerpc/kernel/syscall.c +++ b/arch/powerpc/kernel/syscall.c @@ -18,8 +18,10 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0) long ret; syscall_fn f;- if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0)))+ if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0))) { + clear_thread_flag(TIF_SYSCALL_RET); return syscall_get_error(current, regs); + }if (unlikely(test_and_clear_thread_flag(TIF_SYSCALL_RET)))return syscall_get_error(current, regs); -- 2.47.3
