[parted-devel] aix.c: Avoid memory overrun. Don't assume logical sector size <= 512B

[David Cantrell]

On Thu, 2007-03-08 at 23:41 +0100, Jim Meyering wrote:
> David Cantrell <dcantrell at redhat.com> wrote:
> 
> > On Thu, 2007-03-08 at 22:26 +0100, Jim Meyering wrote:
> >> David Cantrell <dcantrell at redhat.com> wrote:
> >> > On Thu, 2007-03-08 at 15:43 +0100, Jim Meyering wrote:
> >> >> Here's a fix for the first memory overrun bug I found:
> >> >>
> >> >> 	aix.c: Avoid memory overrun.  Don't assume logical sector size <= 512B
> >> >> 	* libparted/labels/aix.c (aix_probe): Return 0 if the
> >> >> 	sector size is larger than our AixLabel size.
> >> >> 	(aix_clobber): Rather than PED_ASSERT'ing that aix_probe returns 1,
> >> >> 	simply return 0 if aix_probe returns fails.
> >> ...
> >> > I like the approach of allocating the required buffer size instead of
> >> > using fixed-size buffers.
> >> >
> >> > Either solution is fine, but I would prefer we go with the ped_malloc()
> >> > approach that's used in amiga_probe so we are consistent throughout
> >> > libparted.
> >>
> >> OK.  I've reworked it and tested the read-only parts.
> ...
> > Should we not be using unsigned int where we're using int?
> 
> Yep.  Good catch.
> Actually, it should probably be uint32_t,
> but if "unsigned int" ever ends up with size different
> from 32 bits, this will be the least of our problems.

Very true.  I would like to think that we're safe with unsigned int and
32-bits for its storage on the platforms we support, but there's always
the corner case.

> Here's an updated patch:
> 
> --------------------
> aix.c: Avoid memory overrun.  Don't assume logical sector size <= 512B
> 
> From: Jim Meyering <jim at meyering.net>
> 
> * libparted/labels/aix.c (struct AixLabel): Remove definition.
> (aix_label_magic_get, aix_label_magic_set): New functions.
> (read_sector): New function.
> (aix_probe): Rewrite not to use the above, and not a static buffer.
> (aix_clobber): Likewise.
> Also, rather than PED_ASSERT'ing that aix_probe returns 1,
> simply return 0 if aix_probe returns fails.
> (ped_disk_aix_init): Remove assertion, now that AixLabel is gone.
> ---
> 
>  libparted/labels/aix.c |   64 ++++++++++++++++++++++++++++++++----------------
>  1 files changed, 43 insertions(+), 21 deletions(-)
> 
> diff --git a/libparted/labels/aix.c b/libparted/labels/aix.c
> index a16ead4..9e7a3e2 100644
> --- a/libparted/labels/aix.c
> +++ b/libparted/labels/aix.c
> @@ -33,45 +33,68 @@
>  #  define _(String) (String)
>  #endif /* ENABLE_NLS */
>  
> -typedef struct {
> -	unsigned int   magic;        /* expect AIX_LABEL_MAGIC */
> -	unsigned int   fillbytes[127];
> -} AixLabel;
> -
>  #define	AIX_LABEL_MAGIC		0xc9c2d4c1
>  
>  static PedDiskType aix_disk_type;
>  
> -static int
> -aix_probe (const PedDevice *dev)
> +static inline int
> +aix_label_magic_get (const char *label)
>  {
> -	AixLabel	label;
> +	return *(unsigned int *)label;
> +}
>  
> -	PED_ASSERT (dev != NULL, return 0);
> +static inline void
> +aix_label_magic_set (char *label, int magic_val)
> +{
> +	*(unsigned int *)label = magic_val;
> +}
>  
> -	if (!ped_device_read (dev, &label, 0, 1))
> +/* Read a single sector, of length DEV->sector_size, into malloc'd storage.
> +   If the read fails, free the memory and return zero without modifying *BUF.
> +   Otherwise, set *BUF to the new buffer and return 1.  */
> +static int
> +read_sector (const PedDevice *dev, char **buf)
> +{
> +	char *b = ped_malloc (dev->sector_size);
> +	PED_ASSERT (b != NULL, return 0);
> +	if (!ped_device_read (dev, b, 0, 1)) {
> +		ped_free (b);
>  		return 0;
> +	}
> +	*buf = b;
> +	return 1;
> +}
>  
> -	if (PED_BE32_TO_CPU (label.magic) != AIX_LABEL_MAGIC)
> -		return 0;
> +static int
> +aix_probe (const PedDevice *dev)
> +{
> +	PED_ASSERT (dev != NULL, return 0);
>  
> -	return 1;
> +	char *label;
> +	if (!read_sector (dev, &label))
> +		return 0;
> +	unsigned int magic = aix_label_magic_get (label);
> +	ped_free (label);
> +	return magic == AIX_LABEL_MAGIC;
>  }
>  
>  #ifndef DISCOVER_ONLY
>  static int
>  aix_clobber (PedDevice* dev)
>  {
> -	AixLabel label;
> -
>  	PED_ASSERT (dev != NULL, return 0);
> -	PED_ASSERT (aix_probe (dev), return 0);
>  
> -	if (!ped_device_read (dev, &label, 0, 1))
> +	if (!aix_probe (dev))
>  		return 0;
> -	
> -	label.magic = 0;
> -	return ped_device_write (dev, &label, 0, 1);
> +
> +	char *label;
> +	if (!read_sector (dev, &label))
> +		return 0;
> +
> +	aix_label_magic_set (label, 0);
> +	int result = ped_device_write (dev, label, 0, 1);
> +	ped_free (label);
> +	return result;
>  }
>  #endif /* !DISCOVER_ONLY */
>  
> @@ -263,7 +286,6 @@ static PedDiskType aix_disk_type = {
>  void
>  ped_disk_aix_init ()
>  {
> -	PED_ASSERT (sizeof (AixLabel) == 512, return);
>  	ped_disk_type_register (&aix_disk_type);
>  }

ACK.

-- 
David Cantrell <dcantrell at redhat.com>
Red Hat / Westford, MA
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