drm/amdgpu/vcn4: Avoid overflow on msg bound check

commit 65bce27 upstream.

As pointed out by SDL, the previous condition may be vulnerable to
overflow.

Fixes: 0a78f2b ("drm/amdgpu/vcn4: Prevent OOB reads when parsing dec msg")
Cc: SDL <sdl@nppct.ru>
Signed-off-by: Benjamin Cheng <benjamin.cheng@amd.com>
Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 3c5367d)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: lolzballs

drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c

@@ -1731,14 +1731,16 @@ static int vcn_v4_0_dec_msg(struct amdgpu_cs_parser *p, struct amdgpu_job *job,
 
 	for (i = 0, msg = &msg[6]; i < num_buffers; ++i, msg += 4) {
 		uint32_t offset, size, *create;
+		uint64_t buf_end;
 
 		if (msg[0] != RDECODE_MESSAGE_CREATE)
 			continue;
 
 		offset = msg[1];
 		size = msg[2];
 
-		if (size < 4 || offset + size > end - addr) {
+		if (size < 4 || check_add_overflow(offset, size, &buf_end) ||
+		    buf_end > end - addr) {
 			DRM_ERROR("VCN message buffer exceeds BO bounds!\n");
 			r = -EINVAL;
 			goto out;