linux-kernel - [PATCH 3.12 07/72] pstore: Fix buffer overflow while write offset equal to buffer size

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Date:   Mon,  7 Nov 2016 14:04:14 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Liu ShuoX <shuox.liu@...el.com>,
        Tony Luck <tony.luck@...el.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 07/72] pstore: Fix buffer overflow while write offset equal to buffer size

From: Liu ShuoX <shuox.liu@...el.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 017321cf390045dd4c4afc4a232995ea50bcf66d upstream.

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@...el.com>
Acked-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 bda61a759b68..0b367ef7a7d6 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);
 
-- 
2.10.2