ARM: 7851/1: check for number of arguments in syscall_get/set_arguments()

In ftrace_syscall_enter(),
    syscall_get_arguments(..., 0, n, ...)
        if (i == 0) { <handle ORIG_r0> ...; n--;}
        memcpy(..., n * sizeof(args[0]));
If 'number of arguments(n)' is zero and 'argument index(i)' is also zero in
syscall_get_arguments(), none of arguments should be copied by memcpy().
Otherwise 'n--' can be a big positive number and unexpected amount of data
will be copied. Tracing system calls which take no argument, say sync(void),
may hit this case and eventually make the system corrupted.
This patch fixes the issue both in syscall_get_arguments() and
syscall_set_arguments().

Cc: <stable@vger.kernel.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h
index f1d96d4e8092a652aeb84f5825082a8f9064cd20..73ddd7239b33aa77d178ae1341c0c46c736a08e5 100644 (file)
--- a/arch/arm/include/asm/syscall.h
+++ b/arch/arm/include/asm/syscall.h
@@ -57,6 +57,9 @@ static inline void syscall_get_arguments(struct task_struct *task,
                                         unsigned int i, unsigned int n,
                                         unsigned long *args)
 {
+       if (n == 0)
+               return;
+
        if (i + n > SYSCALL_MAX_ARGS) {
                unsigned long *args_bad = args + SYSCALL_MAX_ARGS - i;
                unsigned int n_bad = n + i - SYSCALL_MAX_ARGS;
@@ -81,6 +84,9 @@ static inline void syscall_set_arguments(struct task_struct *task,
                                         unsigned int i, unsigned int n,
                                         const unsigned long *args)
 {
+       if (n == 0)
+               return;
+
        if (i + n > SYSCALL_MAX_ARGS) {
                pr_warning("%s called with max args %d, handling only %d\n",
                           __func__, i + n, SYSCALL_MAX_ARGS);