From b99debf92f590200a441b215fb8546c6ae6fdaab Mon Sep 17 00:00:00 2001
From: "Todd C. Miller" <Todd.Miller@sudo.ws>
Date: Thu, 12 May 2022 10:23:27 -0600
Subject: [PATCH] Add arm-specific code to set the system call number. Fixes
 rejection of commands due to policy on arm when in intercept mode.

---
 src/exec_ptrace.c | 12 ++++++------
 src/exec_ptrace.h | 25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/src/exec_ptrace.c b/src/exec_ptrace.c
index 40782386f..26c7f669c 100644
--- a/src/exec_ptrace.c
+++ b/src/exec_ptrace.c
@@ -84,12 +84,12 @@ get_syscallno(struct sudo_ptrace_regs *regs)
 }
 
 static inline void
-set_syscallno(struct sudo_ptrace_regs *regs, int syscallno)
+set_syscallno(pid_t pid, struct sudo_ptrace_regs *regs, int syscallno)
 {
     if (regs->compat) {
-	compat_reg_syscall(regs->u.compat) = syscallno;
+	compat_reg_set_syscall(regs->u.compat, syscallno);
     } else {
-	reg_syscall(regs->u.native) = syscallno;
+	reg_set_syscall(regs->u.native, syscallno);
     }
 }
 
@@ -194,9 +194,9 @@ get_syscallno(struct sudo_ptrace_regs *regs)
 }
 
 static inline void
-set_syscallno(struct sudo_ptrace_regs *regs, int syscallno)
+set_syscallno(pid_t pid, struct sudo_ptrace_regs *regs, int syscallno)
 {
-    reg_syscall(regs->u.native) = syscallno;
+    reg_set_syscall(regs->u.native, syscallno);
 }
 
 static inline unsigned long
@@ -687,7 +687,7 @@ ptrace_fail_syscall(pid_t pid, struct sudo_ptrace_regs *regs, int ecode)
     debug_decl(ptrace_fail_syscall, SUDO_DEBUG_EXEC);
 
     /* Cause the syscall to fail by changing its number to -1. */
-    set_syscallno(regs, -1);
+    set_syscallno(pid, regs, -1);
     if (!ptrace_setregs(pid, regs)) {
 	sudo_warn(U_("unable to set registers for process %d"), (int)pid);
 	debug_return_bool(false);
diff --git a/src/exec_ptrace.h b/src/exec_ptrace.h
index 1927a539e..722538852 100644
--- a/src/exec_ptrace.h
+++ b/src/exec_ptrace.h
@@ -74,6 +74,13 @@
 # define reg_arg2(x)		(x).regs[1]	/* x1 */
 # define reg_arg3(x)		(x).regs[2]	/* x2 */
 # define reg_arg4(x)		(x).regs[3]	/* x3 */
+# define reg_set_syscall(_r, _nr) do {					\
+    struct iovec _iov;							\
+    long syscallno = (_nr);						\
+    _iov.iov_base = &syscallno;						\
+    _iov.iov_len = sizeof(syscallno);					\
+    ptrace(PTRACE_SETREGSET, pid, NT_ARM_SYSTEM_CALL, &_iov);		\
+} while (0)
 #elif defined(__arm__)
 /* Note: assumes arm EABI, not OABI */
 /* Untested */
@@ -86,6 +93,9 @@
 # define reg_arg2(x)		(x).ARM_r1
 # define reg_arg3(x)		(x).ARM_r2
 # define reg_arg4(x)		(x).ARM_r3
+# define reg_set_syscall(_r, _nr) do {					\
+    ptrace(PTRACE_SET_SYSCALL, pid, NULL, _nr);				\
+} while (0)
 #elif defined (__hppa__)
 /* Untested (should also support hppa64) */
 # define SECCOMP_AUDIT_ARCH	AUDIT_ARCH_PARISC
@@ -228,6 +238,9 @@ struct arm_pt_regs {
 # define compat_reg_arg2(x)		(x).uregs[1]	/* r1 */
 # define compat_reg_arg3(x)		(x).uregs[2]	/* r2 */
 # define compat_reg_arg4(x)		(x).uregs[3]	/* r3 */
+# define compat_reg_set_syscall(_r, _nr) do {				\
+    ptrace(PTRACE_SET_SYSCALL, pid, NULL, _nr);				\
+} while (0)
 #elif defined(__powerpc64__)
 struct ppc_pt_regs {
     unsigned int gpr[32];
@@ -263,6 +276,18 @@ struct ppc_pt_regs {
 # define compat_reg_set_retval(_r, _v)	reg_set_retval(_r, _v)
 #endif
 
+/* Set the syscall number the "normal" way by default. */
+#ifndef reg_set_syscall
+# define reg_set_syscall(_r, _nr) do {					\
+    reg_syscall(_r) = (_nr);						\
+} while (0)
+#endif
+#ifndef compat_reg_set_syscall
+# define compat_reg_set_syscall(_r, _nr) do {				\
+    compat_reg_syscall(_r) = (_nr);					\
+} while (0)
+#endif
+
 /* Set the syscall return value the "normal" way by default. */
 #ifndef reg_set_retval
 # define reg_set_retval(_r, _v) do {					\