parisc: Fix ptrace syscall number modification (ebe390b4) · Commits · e / devices / android_kernel_fairphone_FP4

commit b7dc5a071ddf69c0350396b203cba32fe5bab510 upstream. Commit ("parisc: Fix and enable seccomp filter support") introduced a regression in ptrace-based syscall tampering: when tracer changes syscall number to -1, the kernel fails to initialize %r28 with -ENOSYS and subsequently fails to return the error code of the failed syscall to userspace. This erroneous behaviour could be observed with a simple strace syscall fault injection command which is expected to print something like this: $ strace -a0 -ewrite -einject=write:error=enospc echo hello write(1, "hello\n", 6) = -1 ENOSPC (No space left on device) (INJECTED) write(2, "echo: ", 6) = -1 ENOSPC (No space left on device) (INJECTED) write(2, "write error", 11) = -1 ENOSPC (No space left on device) (INJECTED) write(2, "\n", 1) = -1 ENOSPC (No space left on device) (INJECTED) +++ exited with 1 +++ After commit it loops printing something like this instead: write(1, "hello\n", 6../strace: Failed to tamper with process 12345: unexpectedly got no error (return value 0, error 0) ) = 0 (INJECTED) This bug was found by strace test suite. Fixes: ("parisc: Fix and enable seccomp filter support") Cc: stable@vger.kernel.org # v4.5+ Signed-off-by:

Dmitry V. Levin <ldv@altlinux.org> Tested-by:

Helge Deller <deller@gmx.de> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/parisc/kernel/ptrace.c

+21 −8

Original line number	Original line	Diff line number	Diff line
	@@ -308,15 +308,29 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,

	long do_syscall_trace_enter(struct pt_regs *regs)		long do_syscall_trace_enter(struct pt_regs *regs)
	{		{
	if (test_thread_flag(TIF_SYSCALL_TRACE) &&		if (test_thread_flag(TIF_SYSCALL_TRACE)) {
	tracehook_report_syscall_entry(regs)) {		int rc = tracehook_report_syscall_entry(regs);

	/*		/*
	* Tracing decided this syscall should not happen or the		* As tracesys_next does not set %r28 to -ENOSYS
	* debugger stored an invalid system call number. Skip		* when %r20 is set to -1, initialize it here.
	* the system call and the system call restart handling.		*/
			regs->gr[28] = -ENOSYS;

			if (rc) {
			/*
			* A nonzero return code from
			* tracehook_report_syscall_entry() tells us
			* to prevent the syscall execution. Skip
			* the syscall call and the syscall restart handling.
			*
			* Note that the tracer may also just change
			* regs->gr[20] to an invalid syscall number,
			* that is handled by tracesys_next.
	*/		*/
	regs->gr[20] = -1UL;		regs->gr[20] = -1UL;
	goto out;		return -1;
			}
	}		}

	/* Do the secure computing check after ptrace. */		/* Do the secure computing check after ptrace. */
	@@ -340,7 +354,6 @@ long do_syscall_trace_enter(struct pt_regs *regs)
	regs->gr[24] & 0xffffffff,		regs->gr[24] & 0xffffffff,
	regs->gr[23] & 0xffffffff);		regs->gr[23] & 0xffffffff);

	out:
	/*		/*
	* Sign extend the syscall number to 64bit since it may have been		* Sign extend the syscall number to 64bit since it may have been
	* modified by a compat ptrace call		* modified by a compat ptrace call