scatterlist: prevent invalid free when alloc fails

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.

Signed-off-by: Jeffrey Carlyle <jeff.carlyle@motorola.com>
Signed-off-by: Olusanya Soyannwo <c23746@motorola.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index a5ec42868f99..4ceb05d772ae 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -248,8 +248,18 @@ int __sg_alloc_table(struct sg_table *table, unsigned int nents,
                 left -= sg_size;
 
                 sg = alloc_fn(alloc_size, gfp_mask);
-                if (unlikely(!sg))
-                        return -ENOMEM;
+                if (unlikely(!sg)) {
+                        /*
+                         * Adjust entry count to reflect that the last
+                         * entry of the previous table won't be used for
+                         * linkage.  Without this, sg_kfree() may get
+                         * confused.
+                         */
+                        if (prv)
+                                table->nents = ++table->orig_nents;
+
+                        return -ENOMEM;
+                }
 
                 sg_init_table(sg, alloc_size);
                 table->nents = table->orig_nents += sg_size;