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Subject[PATCH] scatterlist: prevent invalid free when alloc fails
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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;

@@ -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]);
return -ENOMEM;
+ }
+
+ total_alloc += alloc_size;

sg_init_table(sg, alloc_size);
table->nents = table->orig_nents += sg_size;
--
1.6.3.3

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