scatterlist: prevent invalid free when alloc fails
Jeffrey Carlyle [Mon, 30 Aug 2010 17:55:09 +0000 (19:55 +0200)]
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>

lib/scatterlist.c

index a5ec428..4ceb05d 100644 (file)
@@ -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;