Messages in this thread | | | Date | Fri, 27 Aug 2010 12:18:57 +0200 | From | Tejun Heo <> | Subject | Re: [PATCH] scatterlist: prevent invalid free when alloc fails |
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Hello,
First of all, the patch is line-wrapped. Please check your email settings.
On 08/26/2010 06:04 PM, Jeffrey Carlyle wrote: > When alloc fails, free_table is being called. Depending on the number of > bytes requested, we determine if we are going to call _get_free_page() > or kmalloc(). When alloc fails, our math is wrong (due to sg_size - 1), > and the last buffer is wrongfully assumed to have been allocated by > kmalloc. Hence, kfree gets called and a panic occurs. > > This fix sets the end marker and allows the proper freeing of the > buffers. > > Signed-off-by: Olusanya Soyannwo <c23746@motorola.com> > Cc: Tejun Heo <tj@kernel.org> > Cc: Jens Axboe <jaxboe@fusionio.com> > Signed-off-by: Jeffrey Carlyle <jeff.carlyle@motorola.com> > --- > lib/scatterlist.c | 11 +++++++++-- > 1 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/lib/scatterlist.c b/lib/scatterlist.c > index a5ec428..acf2c6e 100644 > --- a/lib/scatterlist.c > +++ b/lib/scatterlist.c > @@ -163,7 +163,7 @@ void __sg_free_table(struct sg_table *table, > unsigned int max_ents, > return; > > sgl = table->sgl; > - while (table->orig_nents) { > + while (table->orig_nents && sgl) { > unsigned int alloc_size = table->orig_nents; > unsigned int sg_size;
Why is this change necessary?
> @@ -227,6 +227,7 @@ int __sg_alloc_table(struct sg_table *table, > unsigned int nents, > { > struct scatterlist *sg, *prv; > unsigned int left; > + unsigned int total_alloc = 0; > > #ifndef ARCH_HAS_SG_CHAIN > BUG_ON(nents > max_ents); > @@ -248,8 +249,14 @@ int __sg_alloc_table(struct sg_table *table, > unsigned int nents, > left -= sg_size; > > sg = alloc_fn(alloc_size, gfp_mask); > - if (unlikely(!sg)) > + if (unlikely(!sg)) { > + table->orig_nents = total_alloc; > + /* mark the end of previous entry */ > + sg_mark_end(&prv[alloc_size - 1]);
prv[alloc_size - 1] is already marked as end by sg_init_table() during the previous iteration. Also, prv can be NULL at this point. AFAICS, the only thing necessary would be "if (prv) table->nents++", no?
Thanks.
-- tejun
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