[PATCH 5.4 11/27] bpf: Explicitly memset the bpf_attr structure

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

commit 8096f229421f7b22433775e928d506f0342e5907 upstream.

For the bpf syscall, we are relying on the compiler to properly zero out
the bpf_attr union that we copy userspace data into. Unfortunately that
doesn't always work properly, padding and other oddities might not be
correctly zeroed, and in some tests odd things have been found when the
stack is pre-initialized to other values.

Fix this by explicitly memsetting the structure to 0 before using it.

Reported-by: Maciej Åenczykowski <maze@xxxxxxxxxx>
Reported-by: John Stultz <john.stultz@xxxxxxxxxx>
Reported-by: Alexander Potapenko <glider@xxxxxxxxxx>
Reported-by: Alistair Delva <adelva@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
Link: https://android-review.googlesource.com/c/kernel/common/+/1235490
Link: https://lore.kernel.org/bpf/20200320094813.GA421650@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/bpf/syscall.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2836,7 +2836,7 @@ out:
 
 SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
 {
-	union bpf_attr attr = {};
+	union bpf_attr attr;
 	int err;
 
 	if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN))
@@ -2848,6 +2848,7 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf
 	size = min_t(u32, size, sizeof(attr));
 
 	/* copy attributes from user space, may be less than sizeof(bpf_attr) */
+	memset(&attr, 0, sizeof(attr));
 	if (copy_from_user(&attr, uattr, size) != 0)
 		return -EFAULT;