From: H. Peter Anvin <hpa@zytor.com>
Date: Fri, 11 Dec 2009 23:48:23 +0000 (-0800)
Subject: nvram: Fix write beyond end condition; prove to gcc copy is safe
X-Git-Tag: v2.6.27.51~11
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=8f0b4f678e7f82e415413643a22604925929a157;p=thirdparty%2Fkernel%2Fstable.git

nvram: Fix write beyond end condition; prove to gcc copy is safe

commit a01c7800420d2c294ca403988488a635d4087a6d upstream.

In nvram_write, first of all, correctly handle the case where the file
pointer is already beyond the end; we should return EOF in that case.

Second, make the logic a bit more explicit so that gcc can statically
prove that the copy_from_user() is safe.  Once the condition of the
beyond-end filepointer is eliminated, the copy is safe but gcc can't
prove it, causing build failures for i386 allyesconfig.

Third, eliminate the entirely superfluous variable "len", and just use
the passed-in variable "count" instead.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Wim Van Sebroeck <wim@iguana.be>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <tip-*@git.kernel.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

diff --git a/drivers/char/nvram.c b/drivers/char/nvram.c
index 39f6357e3b5d0..1a5d40daeb8ff 100644
--- a/drivers/char/nvram.c
+++ b/drivers/char/nvram.c
@@ -265,10 +265,16 @@ nvram_write(struct file *file, const char __user *buf, size_t count, loff_t *ppo
 	unsigned char contents[NVRAM_BYTES];
 	unsigned i = *ppos;
 	unsigned char *tmp;
-	int len;
 
-	len = (NVRAM_BYTES - i) < count ? (NVRAM_BYTES - i) : count;
-	if (copy_from_user(contents, buf, len))
+	if (i >= NVRAM_BYTES)
+		return 0;	/* Past EOF */
+
+	if (count > NVRAM_BYTES - i)
+		count = NVRAM_BYTES - i;
+	if (count > NVRAM_BYTES)
+		return -EFAULT;	/* Can't happen, but prove it to gcc */
+
+	if (copy_from_user(contents, buf, count))
 		return -EFAULT;
 
 	spin_lock_irq(&rtc_lock);
@@ -276,7 +282,7 @@ nvram_write(struct file *file, const char __user *buf, size_t count, loff_t *ppo
 	if (!__nvram_check_checksum())
 		goto checksum_err;
 
-	for (tmp = contents; count-- > 0 && i < NVRAM_BYTES; ++i, ++tmp)
+	for (tmp = contents; count--; ++i, ++tmp)
 		__nvram_write_byte(*tmp, i);
 
 	__nvram_set_checksum();