[PATCH 4.9 121/159] iommu/omap: Fix buffer overflow in debugfs

[Greg Kroah-Hartman]

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

[ Upstream commit 184233a5202786b20220acd2d04ddf909ef18f29 ]

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@xxxxxxxxxx>
Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/YuvYh1JbE3v+abd5@kili
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/iommu/omap-iommu-debug.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/omap-iommu-debug.c b/drivers/iommu/omap-iommu-debug.c
index cec33e90e399..a15c4d99b888 100644
--- a/drivers/iommu/omap-iommu-debug.c
+++ b/drivers/iommu/omap-iommu-debug.c
@@ -35,12 +35,12 @@ 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
-- 
2.35.1