Despite that /dev/mem has a size of 0, the check preventing
out-of-bounds access works for /dev/mem as well, because of unsigned
wrap around. Corner case is when offset is zero. There will be no wrap
around and
count = min(count, 0 - 0) = 0
Leading to unexpected behavior with e.g.
memcmp -s /dev/mem 0
on systems without MMU. Fix this.
Signed-off-by: Ahmad Fatoum <ahmad@xxxxxx>
---
fs/devfs-core.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/devfs-core.c b/fs/devfs-core.c
index 3715e543e632..2d016e0e4861 100644
--- a/fs/devfs-core.c
+++ b/fs/devfs-core.c
@@ -573,7 +573,10 @@ ssize_t mem_copy(struct device_d *dev, void *dst, const void *src,
if (!dev || dev->num_resources < 1)
return -1;
- count = size = min(count, resource_size(&dev->resource[0]) - offset);
+ if (resource_size(&dev->resource[0]) > 0 || offset != 0)
+ count = min(count, resource_size(&dev->resource[0]) - offset);
+
+ size = count;
/* no rwsize specification given. Do whatever memcpy likes best */
if (!rwsize) {
--
2.33.0
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