From fb44d589bf3148e13452185a6e772a7efbf2d684 Mon Sep 17 00:00:00 2001 From: Ashutosh Desai Date: Wed, 15 Apr 2026 05:00:00 +0000 Subject: drm/v3d: Reject empty multisync extension to prevent infinite loop MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit v3d_get_extensions() walks a userspace-provided singly-linked list of ioctl extensions without any bound on the chain length. A local user can craft a self-referential extension (ext->next == &ext) with zero in_sync_count and out_sync_count, which bypasses the existing duplicate- extension guard: if (se->in_sync_count || se->out_sync_count) return -EINVAL; The guard never fires because v3d_get_multisync_post_deps() returns immediately when count is zero, leaving both fields at zero on every iteration. The result is an infinite loop in kernel context, blocking the calling thread and pegging a CPU core indefinitely. Fix this by rejecting a multisync extension where both in_sync_count and out_sync_count are zero in v3d_get_multisync_submit_deps(). An empty multisync carries no synchronization information and serves no useful purpose, so returning -EINVAL for such an extension is the correct defense against this attack vector. Fixes: e4165ae8304e ("drm/v3d: add multiple syncobjs support") Cc: stable@vger.kernel.org Signed-off-by: Ashutosh Desai Link: https://patch.msgid.link/20260415050000.3816128-1-ashutoshdesai993@gmail.com Signed-off-by: Maíra Canal --- drivers/gpu/drm/v3d/v3d_submit.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'drivers') diff --git a/drivers/gpu/drm/v3d/v3d_submit.c b/drivers/gpu/drm/v3d/v3d_submit.c index 18f2bf1fe89f..fc74351efad5 100644 --- a/drivers/gpu/drm/v3d/v3d_submit.c +++ b/drivers/gpu/drm/v3d/v3d_submit.c @@ -393,6 +393,11 @@ v3d_get_multisync_submit_deps(struct drm_file *file_priv, if (multisync.pad) return -EINVAL; + if (!multisync.in_sync_count && !multisync.out_sync_count) { + drm_dbg(&v3d->drm, "Empty multisync extension\n"); + return -EINVAL; + } + ret = v3d_get_multisync_post_deps(file_priv, se, multisync.out_sync_count, multisync.out_syncs); if (ret) -- cgit v1.2.3