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scatterlist: add more safeguards 

Add more safeguards to protect against misinterpreting a chain entry
as a normal scatterlist and vice-versa.

* Make sure the entry isn't a chain when assigning and reading a
  normal sg.

* Clear offset and length when chaining.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Tejun Heo 2007-11-27 09:30:39 +01:00 committed by Jens Axboe
parent 7c9f29b128
commit 645a8d9462
1 changed files with 26 additions and 11 deletions
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37
include/linux/scatterlist.h
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@ -26,6 +26,16 @@
#define SG_MAGIC 0x87654321
/*
* We overload the LSB of the page pointer to indicate whether it's
* a valid sg entry, or whether it points to the start of a new scatterlist.
* Those low bits are there for everyone! (thanks mason :-)
*/
#define sg_is_chain(sg) ((sg)->page_link & 0x01)
#define sg_is_last(sg) ((sg)->page_link & 0x02)
#define sg_chain_ptr(sg) \
((struct scatterlist *) ((sg)->page_link & ~0x03))
/**
* sg_assign_page - Assign a given page to an SG entry
* @sg: SG entry
@ -47,6 +57,7 @@ static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
BUG_ON((unsigned long) page & 0x03);
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
BUG_ON(sg_is_chain(sg));
#endif
sg->page_link = page_link | (unsigned long) page;
}
@ -73,7 +84,14 @@ static inline void sg_set_page(struct scatterlist *sg, struct page *page,
sg->length = len;
}
#define sg_page(sg) ((struct page *) ((sg)->page_link & ~0x3))
static inline struct page *sg_page(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
BUG_ON(sg_is_chain(sg));
#endif
return (struct page *)((sg)->page_link & ~0x3);
}
/**
* sg_set_buf - Set sg entry to point at given data
@ -88,16 +106,6 @@ static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
}
/*
* We overload the LSB of the page pointer to indicate whether it's
* a valid sg entry, or whether it points to the start of a new scatterlist.
* Those low bits are there for everyone! (thanks mason :-)
*/
#define sg_is_chain(sg) ((sg)->page_link & 0x01)
#define sg_is_last(sg) ((sg)->page_link & 0x02)
#define sg_chain_ptr(sg) \
((struct scatterlist *) ((sg)->page_link & ~0x03))
/**
* sg_next - return the next scatterlist entry in a list
* @sg: The current sg entry
@ -179,6 +187,13 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
#ifndef ARCH_HAS_SG_CHAIN
BUG();
#endif
/*
* offset and length are unused for chain entry. Clear them.
*/
prv->offset = 0;
prv->length = 0;
/*
* Set lowest bit to indicate a link pointer, and make sure to clear
* the termination bit if it happens to be set.