iommu/omap: Fix buffer overflow in debugfs

There are two issues here:

1) The "len" variable needs to be checked before the very first write.
   Otherwise if omap2_iommu_dump_ctx() with "bytes" less than 32 it is a
   buffer overflow.
2) The snprintf() function returns the number of bytes that *would* have
   been copied if there were enough space.  But we want to know the
   number of bytes which were *actually* copied so use scnprintf()
   instead.

Fixes: bd4396f09a4a ("iommu/omap: Consolidate OMAP IOMMU modules")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/YuvYh1JbE3v+abd5@kili
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/drivers/iommu/omap-iommu-debug.c b/drivers/iommu/omap-iommu-debug.c
index a99afb5..259f652 100644 (file)
--- a/drivers/iommu/omap-iommu-debug.c
+++ b/drivers/iommu/omap-iommu-debug.c
@@ -32,12 +32,12 @@ static inline bool is_omap_iommu_detached(struct omap_iommu *obj)
                ssize_t bytes;                                          \
                const char *str = "%20s: %08x\n";                       \
                const int maxcol = 32;                                  \
-               bytes = snprintf(p, maxcol, str, __stringify(name),     \
+               if (len < maxcol)                                       \
+                       goto out;                                       \
+               bytes = scnprintf(p, maxcol, str, __stringify(name),    \
                                 iommu_read_reg(obj, MMU_##name));      \
                p += bytes;                                             \
                len -= bytes;                                           \
-               if (len < maxcol)                                       \
-                       goto out;                                       \
        } while (0)
 
 static ssize_t