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drm/v3d: Reject empty multisync extension to prevent infinite loop

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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: e4165ae830 ("drm/v3d: add multiple syncobjs support")
Cc: stable@vger.kernel.org
Signed-off-by: Ashutosh Desai <ashutoshdesai993@gmail.com>
Link: https://patch.msgid.link/20260415050000.3816128-1-ashutoshdesai993@gmail.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>
This commit is contained in:
Ashutosh Desai
2026-04-15 05:00:00 +00:00
committed by Maíra Canal
parent 4a92ef0c57
commit fb44d589bf
1 changed files with 5 additions and 0 deletions
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5
drivers/gpu/drm/v3d/v3d_submit.c
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@@ -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)