[PATCH] gen_init_cpio: Avoid race between call to stat() and call to open()

[PATCH] gen_init_cpio: Avoid race between call to stat() and call to open()

[Jesper Juhl]

Hi,

In usr/gen_init_cpio.c::cpio_mkfile() a call to stat() is made based on 
pathname, subsequently the file is open()'ed and then the value of the 
initial stat() call is used to allocate a buffer. This is not safe since 
the file may change between the call to stat() and the call to open().
Safer to just open() the file and then do fstat() using the filedescriptor 
returned by open.


Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
 gen_init_cpio.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
index b2b3c2d..7cd4538 100644
--- a/usr/gen_init_cpio.c
+++ b/usr/gen_init_cpio.c
@@ -303,18 +303,18 @@ static int cpio_mkfile(const char *name, const char *location,
 
 	mode |= S_IFREG;
 
-	retval = stat (location, &buf);
-	if (retval) {
-		fprintf (stderr, "File %s could not be located\n", location);
-		goto error;
-	}
-
 	file = open (location, O_RDONLY);
 	if (file < 0) {
 		fprintf (stderr, "File %s could not be opened for reading\n", location);
 		goto error;
 	}
 
+	retval = fstat (file, &buf);
+	if (retval) {
+		fprintf (stderr, "File %s could not be stat()'ed\n", location);
+		goto error;
+	}
+
 	filebuf = malloc(buf.st_size);
 	if (!filebuf) {
 		fprintf (stderr, "out of memory\n");




-- 
Jesper Juhl <jj@chaosbits.net>            http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.

Re: [PATCH] gen_init_cpio: Avoid race between call to stat() and call to open()

[Jesper Juhl]

Bad subject.
Better subject: Avoid risk of file changing between calls to stat() and open().

-- 
Jesper Juhl <jj@chaosbits.net>            http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.

Re: [PATCH] gen_init_cpio: Avoid race between call to stat() and call to open()

[Jeff Garzik]

On 12/24/2010 03:28 PM, Jesper Juhl wrote:
> Hi,
>
> In usr/gen_init_cpio.c::cpio_mkfile() a call to stat() is made based on
> pathname, subsequently the file is open()'ed and then the value of the
> initial stat() call is used to allocate a buffer. This is not safe since
> the file may change between the call to stat() and the call to open().
> Safer to just open() the file and then do fstat() using the filedescriptor
> returned by open.
>
>
> Signed-off-by: Jesper Juhl<jj@chaosbits.net>

Acked-by: Jeff Garzik <jgarzik@redhat.com>

Re: [PATCH] gen_init_cpio: Avoid race between call to stat() and call to open()

[Michal Marek]

On Fri, Dec 24, 2010 at 05:33:48PM -0500, Jeff Garzik wrote:
> On 12/24/2010 03:28 PM, Jesper Juhl wrote:
> >Hi,
> >
> >In usr/gen_init_cpio.c::cpio_mkfile() a call to stat() is made based on
> >pathname, subsequently the file is open()'ed and then the value of the
> >initial stat() call is used to allocate a buffer. This is not safe since
> >the file may change between the call to stat() and the call to open().
> >Safer to just open() the file and then do fstat() using the filedescriptor
> >returned by open.
> >
> >
> >Signed-off-by: Jesper Juhl<jj@chaosbits.net>
> 
> Acked-by: Jeff Garzik <jgarzik@redhat.com>

Looks like an academic issue to me, but the kernel should promote good
programming practices :). Applied to kbuild-2.6.git#kbuild, thanks.

Michal