[CRYPTO] blkcipher: Fix handling of kmalloc page straddling
The function blkcipher_get_spot tries to return a buffer of
the specified length that does not straddle a page. It has
an off-by-one bug so it may advance a page unnecessarily.
What's worse, one of its callers doesn't provide a buffer
that's sufficiently long for this operation.
This patch fixes both problems. Thanks to Bob Gilligan for
diagnosing this problem and providing a fix.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/blkcipher.c b/crypto/blkcipher.c
index 7755834..97586af 100644
--- a/crypto/blkcipher.c
+++ b/crypto/blkcipher.c
@@ -59,11 +59,13 @@
scatterwalk_unmap(walk->dst.virt.addr, 1);
}
+/* Get a spot of the specified length that does not straddle a page.
+ * The caller needs to ensure that there is enough space for this operation.
+ */
static inline u8 *blkcipher_get_spot(u8 *start, unsigned int len)
{
- if (offset_in_page(start + len) < len)
- return (u8 *)((unsigned long)(start + len) & PAGE_MASK);
- return start;
+ u8 *end_page = (u8 *)(((unsigned long)(start + len - 1)) & PAGE_MASK);
+ return start < end_page ? start : end_page;
}
static inline unsigned int blkcipher_done_slow(struct crypto_blkcipher *tfm,
@@ -155,7 +157,8 @@
if (walk->buffer)
goto ok;
- n = bsize * 2 + (alignmask & ~(crypto_tfm_ctx_alignment() - 1));
+ n = bsize * 3 - (alignmask + 1) +
+ (alignmask & ~(crypto_tfm_ctx_alignment() - 1));
walk->buffer = kmalloc(n, GFP_ATOMIC);
if (!walk->buffer)
return blkcipher_walk_done(desc, walk, -ENOMEM);