Commit 828db212 authored Jun 29, 2017 by James Hogan Committed by Ralf Baechle Jul 11, 2017

MIPS: Traced negative syscalls should return -ENOSYS



If a negative system call number is used when system call tracing is
enabled, syscall_trace_enter() will return that negative system call
number without having written the return value and error flag into the
pt_regs.

The caller then treats it as a cancelled system call and assumes that
the return value and error flag are already written, leaving the
negative system call number in the return register ($v0), and the 4th
system call argument in the error register ($a3).

Add a special case to detect this at the end of syscall_trace_enter(),
to set the return value to error -ENOSYS when this happens.

Fixes: d218af78 ("MIPS: scall: Always run the seccomp syscall filters")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16653/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

parent becddba9

arch/mips/kernel/ptrace.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -894,6 +894,13 @@ asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall)

		audit_syscall_entry(syscall, regs->regs[4], regs->regs[5],
		regs->regs[6], regs->regs[7]);

		/*
		* Negative syscall numbers are mistaken for rejected syscalls, but
		* won't have had the return value set appropriately, so we do so now.
		*/
		if (syscall < 0)
		syscall_set_return_value(current, regs, -ENOSYS, 0);
		return syscall;
		}