There is an integer overflow bug in the FBIOPUTCMAP ioctl if
cmap->len * 2 overflows.
It's harmless, except that it messes up the cmap until someone types
`reset`. It could have been caught by checking the return from
fb_copy_cmap().
Or it could have been caught by limiting the size of the cmaps to one
page. The cmaps are allocated with GFP_ATOMIC and it makes sense to
limit them.
Different drivers use different sizes of cmaps. There are about 150
drivers. I've checked a bunch (50) of them and the larges cmap.len I've
found is gxt4500 which maxes out at 1024 so PAGE_SIZE is about twice that
length. For some of the 50 I wasn't sure on the limit.
Is PAGE_SIZE a reasonable limit? Does anyone know or do I have to audit
all 150 drivers?
diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c
index f53b9f1..6dc5817 100644
--- a/drivers/video/fbcmap.c
+++ b/drivers/video/fbcmap.c
@@ -110,7 +110,9 @@ int fb_alloc_cmap(struct fb_cmap *cmap, int len, int transp)
}
cmap->start = 0;
cmap->len = len;
- fb_copy_cmap(fb_default_cmap(len), cmap);
+ if (fb_copy_cmap(fb_default_cmap(len), cmap))
+ goto fail;
+
return 0;
fail:
@@ -250,6 +252,9 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info)
int rc, size = cmap->len * sizeof(u16);
struct fb_cmap umap;
+ if (cmap->len > PAGE_SIZE || cmap->len * sizeof(u16) > PAGE_SIZE)
+ return -EINVAL;
+
memset(&umap, 0, sizeof(struct fb_cmap));
rc = fb_alloc_cmap(&umap, cmap->len, cmap->transp != NULL);
if (rc)
--
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