[PATCH 1/2] pstore: fix buffer overflow while write offset equal to buffer size

[Liu Shuo]

From: Liu ShuoX <shuox.liu@xxxxxxxxx>

In case new offset is equal to prz->buffer_size, it won't wrap at this
time and will return old(overflow) value next time.

Signed-off-by: Liu ShuoX <shuox.liu@xxxxxxxxx>
---
fs/pstore/ram_core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index de272d4..ff7e3d4 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -54,7 +54,7 @@ static size_t buffer_start_add_atomic(struct persistent_ram_zone *prz, size_t a)
	do {
		old = atomic_read(&prz->buffer->start);
		new = old + a;
-		while (unlikely(new > prz->buffer_size))
+		while (unlikely(new >= prz->buffer_size))
			new -= prz->buffer_size;
	} while (atomic_cmpxchg(&prz->buffer->start, old, new) != old);

@@ -91,7 +91,7 @@ static size_t buffer_start_add_locked(struct persistent_ram_zone *prz, size_t a)

	old = atomic_read(&prz->buffer->start);
	new = old + a;
-	while (unlikely(new > prz->buffer_size))
+	while (unlikely(new >= prz->buffer_size))
		new -= prz->buffer_size;
	atomic_set(&prz->buffer->start, new);

--
1.8.3.2



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