crypto: ablkcipher - fix crash flushing dcache in error path

Like the skcipher_walk and blkcipher_walk cases:

scatterwalk_done() is only meant to be called after a nonzero number of
bytes have been processed, since scatterwalk_pagedone() will flush the
dcache of the *previous* page.  But in the error case of
ablkcipher_walk_done(), e.g. if the input wasn't an integer number of
blocks, scatterwalk_done() was actually called after advancing 0 bytes.
This caused a crash ("BUG: unable to handle kernel paging request")
during '!PageSlab(page)' on architectures like arm and arm64 that define
ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE, provided that the input was
page-aligned as in that case walk->offset == 0.

Fix it by reorganizing ablkcipher_walk_done() to skip the
scatterwalk_advance() and scatterwalk_done() if an error has occurred.

Reported-by: Liu Chao <liuchao741@huawei.com>
Fixes: bf06099db18a ("crypto: skcipher - Add ablkcipher_walk interfaces")
Cc: <stable@vger.kernel.org> # v2.6.35+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 26 insertions, 31 deletions

diff --git a/crypto/ablkcipher.c b/crypto/ablkcipher.c
index 1edb5000d783..8882e90e868e 100644
--- a/crypto/ablkcipher.c
+++ b/crypto/ablkcipher.c
@@ -71,11 +71,9 @@ static inline u8 *ablkcipher_get_spot(u8 *start, unsigned int len)
         return max(start, end_page);
 }
 
-static inline unsigned int ablkcipher_done_slow(struct ablkcipher_walk *walk,
-                                                unsigned int bsize)
+static inline void ablkcipher_done_slow(struct ablkcipher_walk *walk,
+                                        unsigned int n)
 {
-        unsigned int n = bsize;
-
         for (;;) {
                 unsigned int len_this_page = scatterwalk_pagelen(&walk->out);
 
@@ -87,17 +85,13 @@ static inline unsigned int ablkcipher_done_slow(struct ablkcipher_walk *walk,
                 n -= len_this_page;
                 scatterwalk_start(&walk->out, sg_next(walk->out.sg));
         }
-
-        return bsize;
 }
 
-static inline unsigned int ablkcipher_done_fast(struct ablkcipher_walk *walk,
-                                                unsigned int n)
+static inline void ablkcipher_done_fast(struct ablkcipher_walk *walk,
+                                        unsigned int n)
 {
         scatterwalk_advance(&walk->in, n);
         scatterwalk_advance(&walk->out, n);
-
-        return n;
 }
 
 static int ablkcipher_walk_next(struct ablkcipher_request *req,
@@ -107,39 +101,40 @@ int ablkcipher_walk_done(struct ablkcipher_request *req,
                          struct ablkcipher_walk *walk, int err)
 {
         struct crypto_tfm *tfm = req->base.tfm;
-        unsigned int nbytes = 0;
+        unsigned int n; /* bytes processed */
+        bool more;
 
-        if (likely(err >= 0)) {
-                unsigned int n = walk->nbytes - err;
+        if (unlikely(err < 0))
+                goto finish;
 
-                if (likely(!(walk->flags & ABLKCIPHER_WALK_SLOW)))
-                        n = ablkcipher_done_fast(walk, n);
-                else if (WARN_ON(err)) {
-                        err = -EINVAL;
-                        goto err;
-                } else
-                        n = ablkcipher_done_slow(walk, n);
+        n = walk->nbytes - err;
+        walk->total -= n;
+        more = (walk->total != 0);
 
-                nbytes = walk->total - n;
-                err = 0;
+        if (likely(!(walk->flags & ABLKCIPHER_WALK_SLOW))) {
+                ablkcipher_done_fast(walk, n);
+        } else {
+                if (WARN_ON(err)) {
+                        /* unexpected case; didn't process all bytes */
+                        err = -EINVAL;
+                        goto finish;
+                }
+                ablkcipher_done_slow(walk, n);
         }
 
-        scatterwalk_done(&walk->in, 0, nbytes);
-        scatterwalk_done(&walk->out, 1, nbytes);
-
-err:
-        walk->total = nbytes;
-        walk->nbytes = nbytes;
+        scatterwalk_done(&walk->in, 0, more);
+        scatterwalk_done(&walk->out, 1, more);
 
-        if (nbytes) {
+        if (more) {
                 crypto_yield(req->base.flags);
                 return ablkcipher_walk_next(req, walk);
         }
-
+        err = 0;
+finish:
+        walk->nbytes = 0;
         if (walk->iv != req->info)
                 memcpy(req->info, walk->iv, tfm->crt_ablkcipher.ivsize);
         kfree(walk->iv_buffer);
-
         return err;
 }
 EXPORT_SYMBOL_GPL(ablkcipher_walk_done);