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: d218af78492a ("MIPS: scall: Always run the seccomp syscall filters")
Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
---
arch/mips/kernel/ptrace.c | 7 +++++++
1 file changed, 7 insertions(+), 0 deletions(-)
diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index 8e2ea86dc23e..6dd13641a418 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -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;
}
--
git-series 0.8.10
