[PATCH stable v5.4+] s390/ptrace: return -ENOSYS when invalid syscall is supplied

[Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>]

From: Sven Schnelle <svens@linux.ibm.com>

commit cd29fa798001075a554b978df3a64e6656c25794 upstream.

The current code returns the syscall number which an invalid
syscall number is supplied and tracing is enabled. This makes
the strace testsuite fail.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Dan Streetman <ddstreet@canonical.com>
Link: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1895132
[krzysztof: adjusted the backport around missing ifdef CONFIG_SECCOMP,
 add Link and Fixes; apparently this should go with the referenced commit]
Fixes: 00332c16b160 ("s390/ptrace: pass invalid syscall numbers to tracing")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 arch/s390/kernel/ptrace.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/s390/kernel/ptrace.c b/arch/s390/kernel/ptrace.c
index c6aef2ecf289..ad74472ce967 100644
--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -867,6 +867,7 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
 {
 	unsigned long mask = -1UL;
+	long ret = -1;
 
 	/*
 	 * The sysc_tracesys code in entry.S stored the system
@@ -878,27 +879,33 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
 		 * Tracing decided this syscall should not happen. Skip
 		 * the system call and the system call restart handling.
 		 */
-		clear_pt_regs_flag(regs, PIF_SYSCALL);
-		return -1;
+		goto skip;
 	}
 
 	/* Do the secure computing check after ptrace. */
 	if (secure_computing(NULL)) {
 		/* seccomp failures shouldn't expose any additional code. */
-		return -1;
+		goto skip;
 	}
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
-		trace_sys_enter(regs, regs->gprs[2]);
+		trace_sys_enter(regs, regs->int_code & 0xffff);
 
 	if (is_compat_task())
 		mask = 0xffffffff;
 
-	audit_syscall_entry(regs->gprs[2], regs->orig_gpr2 & mask,
+	audit_syscall_entry(regs->int_code & 0xffff, regs->orig_gpr2 & mask,
 			    regs->gprs[3] &mask, regs->gprs[4] &mask,
 			    regs->gprs[5] &mask);
 
+	if ((signed long)regs->gprs[2] >= NR_syscalls) {
+		regs->gprs[2] = -ENOSYS;
+		ret = -ENOSYS;
+	}
 	return regs->gprs[2];
+skip:
+	clear_pt_regs_flag(regs, PIF_SYSCALL);
+	return ret;
 }
 
 asmlinkage void do_syscall_trace_exit(struct pt_regs *regs)
-- 
2.25.1