PATCH: fix 2 byte data leak due to padding

PATCH: fix 2 byte data leak due to padding

[Alan Cox]

diff -u --new-file --recursive --exclude-from /usr/src/exclude linux-2.6.0-test2/fs/stat.c linux-2.6.0-test2-ac1/fs/stat.c
--- linux-2.6.0-test2/fs/stat.c	2003-07-14 14:11:56.000000000 +0100
+++ linux-2.6.0-test2-ac1/fs/stat.c	2003-07-23 16:27:42.000000000 +0100
@@ -106,7 +106,7 @@
 {
 	static int warncount = 5;
 	struct __old_kernel_stat tmp;
-
+	
 	if (warncount > 0) {
 		warncount--;
 		printk(KERN_WARNING "VFS: Warning: %s using old stat() call. Recompile your binary.\n",
@@ -116,6 +116,7 @@
 		warncount = 0;
 	}
 
+	memset(&tmp, 0, sizeof(struct __old_kernel_stat));
 	tmp.st_dev = stat->dev;
 	tmp.st_ino = stat->ino;
 	tmp.st_mode = stat->mode;

Re: PATCH: fix 2 byte data leak due to padding

[Lou Langholtz]

Alan Cox wrote:

>diff -u --new-file --recursive --exclude-from /usr/src/exclude linux-2.6.0-test2/fs/stat.c linux-2.6.0-test2-ac1/fs/stat.c
>--- linux-2.6.0-test2/fs/stat.c	2003-07-14 14:11:56.000000000 +0100
>+++ linux-2.6.0-test2-ac1/fs/stat.c	2003-07-23 16:27:42.000000000 +0100
>@@ -106,7 +106,7 @@
> {
> 	static int warncount = 5;
> 	struct __old_kernel_stat tmp;
>-
>+	
> 	if (warncount > 0) {
> 		warncount--;
> 		printk(KERN_WARNING "VFS: Warning: %s using old stat() call. Recompile your binary.\n",
>@@ -116,6 +116,7 @@
> 		warncount = 0;
> 	}
> 
>+	memset(&tmp, 0, sizeof(struct __old_kernel_stat));
>
Wouldn't it be more clear (better) to use sizeof(tmp) here rather than 
sizeof(struct _old_kernel_stat)?

Re: PATCH: fix 2 byte data leak due to padding

[Alan Cox]

On Llu, 2003-07-28 at 04:49, Lou Langholtz wrote:
> >+	memset(&tmp, 0, sizeof(struct __old_kernel_stat));
> >
> Wouldn't it be more clear (better) to use sizeof(tmp) here rather than 
> sizeof(struct _old_kernel_stat)?

sizeof(variable) can be suprising some times so I always use sizeof(type) out
of habit. (Think sizeof(x) when X later becomes a pointer)

Re: PATCH: fix 2 byte data leak due to padding

[Wichert Akkerman]

Previously Alan Cox wrote:
> sizeof(variable) can be suprising some times so I always use sizeof(type) out
> of habit. (Think sizeof(x) when X later becomes a pointer)

when X becomes a pointer and you use sizeof(type of what X points to)
you'll be in trouble anyway.

Wichert.

-- 
Wichert Akkerman <wichert@wiggy.net>    It is simple to make things.
http://www.wiggy.net/                   It is hard to make things simple.

Re: PATCH: fix 2 byte data leak due to padding

[Andrew Morton]

Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
>
> On Llu, 2003-07-28 at 04:49, Lou Langholtz wrote:
> > >+	memset(&tmp, 0, sizeof(struct __old_kernel_stat));
> > >
> > Wouldn't it be more clear (better) to use sizeof(tmp) here rather than 
> > sizeof(struct _old_kernel_stat)?
> 
> sizeof(variable) can be suprising some times so I always use sizeof(type) out
> of habit. (Think sizeof(x) when X later becomes a pointer)

#define memzero(addr) memset(addr, 0, sizeof(*addr))

would robustify a lot of these things...