linux-kernel - [PATCH 4/7] pstore/ram_core: Better ECC size checking

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Date:	Mon, 18 Jun 2012 19:15:53 -0700
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Shuah Khan <shuahkhan@...il.com>, arve@...roid.com,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	Jesper Juhl <jj@...osbits.net>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Thomas Meyer <thomas@...3r.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com
Subject: [PATCH 4/7] pstore/ram_core: Better ECC size checking

- Instead of exploiting unsigned overflows (which doesn't work for all
  sizes), use straightforward checking for ECC total size not exceeding
  initial buffer size;

- Printing overflowed buffer_size is not informative. Instead, print
  ecc_size and buffer_size;

- No need for buffer_size argument in persistent_ram_init_ecc(),
  we can address prz->buffer_size directly.

Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
---
 fs/pstore/ram_core.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index f62ebf2..a5a7b13 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -171,12 +171,12 @@ static void persistent_ram_ecc_old(struct persistent_ram_zone *prz)
 	}
 }
 
-static int persistent_ram_init_ecc(struct persistent_ram_zone *prz,
-	size_t buffer_size)
+static int persistent_ram_init_ecc(struct persistent_ram_zone *prz)
 {
 	int numerr;
 	struct persistent_ram_buffer *buffer = prz->buffer;
 	int ecc_blocks;
+	size_t ecc_total;
 
 	if (!prz->ecc)
 		return 0;
@@ -187,14 +187,14 @@ static int persistent_ram_init_ecc(struct persistent_ram_zone *prz,
 	prz->ecc_poly = 0x11d;
 
 	ecc_blocks = DIV_ROUND_UP(prz->buffer_size, prz->ecc_block_size);
-	prz->buffer_size -= (ecc_blocks + 1) * prz->ecc_size;
-
-	if (prz->buffer_size > buffer_size) {
-		pr_err("persistent_ram: invalid size %zu, non-ecc datasize %zu\n",
-		       buffer_size, prz->buffer_size);
+	ecc_total = (ecc_blocks + 1) * prz->ecc_size;
+	if (ecc_total >= prz->buffer_size) {
+		pr_err("%s: invalid ecc_size %u (total %zu, buffer size %zu)\n",
+		       __func__, prz->ecc_size, ecc_total, prz->buffer_size);
 		return -EINVAL;
 	}
 
+	prz->buffer_size -= ecc_total;
 	prz->par_buffer = buffer->data + prz->buffer_size;
 	prz->par_header = prz->par_buffer + ecc_blocks * prz->ecc_size;
 
@@ -397,7 +397,7 @@ static int __devinit persistent_ram_post_init(struct persistent_ram_zone *prz,
 
 	prz->ecc = ecc;
 
-	ret = persistent_ram_init_ecc(prz, prz->buffer_size);
+	ret = persistent_ram_init_ecc(prz);
 	if (ret)
 		return ret;
 
-- 
1.7.10.4

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