ARM: 7411/1: audit: fix treatment of saved ip register during syscall tracing

The ARM audit code incorrectly uses the saved application ip register
value to infer syscall entry or exit. Additionally, the saved value will
be clobbered if the current task is not being traced, which can lead to
libc corruption if ip is live (apparently glibc uses it for the TLS
pointer).

This patch fixes the syscall tracing code so that the why parameter is
used to infer the syscall direction and the saved ip is only updated if
we know that we will be signalling a ptrace trap.

Reported-and-Tested-by: Jon Masters <jcm@jonmasters.org>

Cc: stable@vger.kernel.org
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 8 insertions, 8 deletions

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 80abafb9bf33..d8dbe9ca66b0 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -916,14 +916,7 @@ asmlinkage int syscall_trace(int why, struct pt_regs *regs, int scno)
 {
         unsigned long ip;
 
-        /*
-         * Save IP.  IP is used to denote syscall entry/exit:
-         *  IP = 0 -> entry, = 1 -> exit
-         */
-        ip = regs->ARM_ip;
-        regs->ARM_ip = why;
-
-        if (!ip)
+        if (why)
                 audit_syscall_exit(regs);
         else
                 audit_syscall_entry(AUDIT_ARCH_NR, scno, regs->ARM_r0,
@@ -936,6 +929,13 @@ asmlinkage int syscall_trace(int why, struct pt_regs *regs, int scno)
 
         current_thread_info()->syscall = scno;
 
+        /*
+         * IP is used to denote syscall entry/exit:
+         * IP = 0 -> entry, =1 -> exit
+         */
+        ip = regs->ARM_ip;
+        regs->ARM_ip = why;
+
         /* the 0x80 provides a way for the tracing parent to distinguish
            between a syscall stop and SIGTRAP delivery */
         ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)