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* [PATCH master] fs: /dev/mem: handle copy at offset 0 correctly
@ 2021-11-29  7:14 Ahmad Fatoum
  2021-12-07  9:13 ` Sascha Hauer
  0 siblings, 1 reply; 2+ messages in thread
From: Ahmad Fatoum @ 2021-11-29  7:14 UTC (permalink / raw)
  To: barebox; +Cc: Ahmad Fatoum

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@a3f.at>
---
 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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2021-11-29  7:14 [PATCH master] fs: /dev/mem: handle copy at offset 0 correctly Ahmad Fatoum
2021-12-07  9:13 ` Sascha Hauer

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