From d2d0727b1654e11563f181f4d3d48b9275514480 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 20 May 2019 09:29:39 -0700 Subject: fscrypt: simplify bounce page handling Currently, bounce page handling for writes to encrypted files is unnecessarily complicated. A fscrypt_ctx is allocated along with each bounce page, page_private(bounce_page) points to this fscrypt_ctx, and fscrypt_ctx::w::control_page points to the original pagecache page. However, because writes don't use the fscrypt_ctx for anything else, there's no reason why page_private(bounce_page) can't just point to the original pagecache page directly. Therefore, this patch makes this change. In the process, it also cleans up the API exposed to filesystems that allows testing whether a page is a bounce page, getting the pagecache page from a bounce page, and freeing a bounce page. Reviewed-by: Chandan Rajendra Signed-off-by: Eric Biggers --- fs/crypto/crypto.c | 104 ++++++++++++++++++----------------------------------- 1 file changed, 34 insertions(+), 70 deletions(-) (limited to 'fs/crypto/crypto.c') diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c index 335a362ee446..881e2a69f8a6 100644 --- a/fs/crypto/crypto.c +++ b/fs/crypto/crypto.c @@ -64,18 +64,11 @@ EXPORT_SYMBOL(fscrypt_enqueue_decrypt_work); * * If the encryption context was allocated from the pre-allocated pool, returns * it to that pool. Else, frees it. - * - * If there's a bounce page in the context, this frees that. */ void fscrypt_release_ctx(struct fscrypt_ctx *ctx) { unsigned long flags; - if (ctx->flags & FS_CTX_HAS_BOUNCE_BUFFER_FL && ctx->w.bounce_page) { - mempool_free(ctx->w.bounce_page, fscrypt_bounce_page_pool); - ctx->w.bounce_page = NULL; - } - ctx->w.control_page = NULL; if (ctx->flags & FS_CTX_REQUIRES_FREE_ENCRYPT_FL) { kmem_cache_free(fscrypt_ctx_cachep, ctx); } else { @@ -100,14 +93,8 @@ struct fscrypt_ctx *fscrypt_get_ctx(gfp_t gfp_flags) unsigned long flags; /* - * We first try getting the ctx from a free list because in - * the common case the ctx will have an allocated and - * initialized crypto tfm, so it's probably a worthwhile - * optimization. For the bounce page, we first try getting it - * from the kernel allocator because that's just about as fast - * as getting it from a list and because a cache of free pages - * should generally be a "last resort" option for a filesystem - * to be able to do its job. + * First try getting a ctx from the free list so that we don't have to + * call into the slab allocator. */ spin_lock_irqsave(&fscrypt_ctx_lock, flags); ctx = list_first_entry_or_null(&fscrypt_free_ctxs, @@ -123,11 +110,31 @@ struct fscrypt_ctx *fscrypt_get_ctx(gfp_t gfp_flags) } else { ctx->flags &= ~FS_CTX_REQUIRES_FREE_ENCRYPT_FL; } - ctx->flags &= ~FS_CTX_HAS_BOUNCE_BUFFER_FL; return ctx; } EXPORT_SYMBOL(fscrypt_get_ctx); +struct page *fscrypt_alloc_bounce_page(gfp_t gfp_flags) +{ + return mempool_alloc(fscrypt_bounce_page_pool, gfp_flags); +} + +/** + * fscrypt_free_bounce_page() - free a ciphertext bounce page + * + * Free a bounce page that was allocated by fscrypt_encrypt_page(), or by + * fscrypt_alloc_bounce_page() directly. + */ +void fscrypt_free_bounce_page(struct page *bounce_page) +{ + if (!bounce_page) + return; + set_page_private(bounce_page, (unsigned long)NULL); + ClearPagePrivate(bounce_page); + mempool_free(bounce_page, fscrypt_bounce_page_pool); +} +EXPORT_SYMBOL(fscrypt_free_bounce_page); + void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num, const struct fscrypt_info *ci) { @@ -186,16 +193,6 @@ int fscrypt_do_page_crypto(const struct inode *inode, fscrypt_direction_t rw, return 0; } -struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx, - gfp_t gfp_flags) -{ - ctx->w.bounce_page = mempool_alloc(fscrypt_bounce_page_pool, gfp_flags); - if (ctx->w.bounce_page == NULL) - return ERR_PTR(-ENOMEM); - ctx->flags |= FS_CTX_HAS_BOUNCE_BUFFER_FL; - return ctx->w.bounce_page; -} - /** * fscypt_encrypt_page() - Encrypts a page * @inode: The inode for which the encryption should take place @@ -210,22 +207,12 @@ struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx, * previously written data. * @gfp_flags: The gfp flag for memory allocation * - * Encrypts @page using the ctx encryption context. Performs encryption - * either in-place or into a newly allocated bounce page. - * Called on the page write path. - * - * Bounce page allocation is the default. - * In this case, the contents of @page are encrypted and stored in an - * allocated bounce page. @page has to be locked and the caller must call - * fscrypt_restore_control_page() on the returned ciphertext page to - * release the bounce buffer and the encryption context. - * - * In-place encryption is used by setting the FS_CFLG_OWN_PAGES flag in - * fscrypt_operations. Here, the input-page is returned with its content - * encrypted. + * Encrypts @page. If the filesystem set FS_CFLG_OWN_PAGES, then the data is + * encrypted in-place and @page is returned. Else, a bounce page is allocated, + * the data is encrypted into the bounce page, and the bounce page is returned. + * The caller is responsible for calling fscrypt_free_bounce_page(). * - * Return: A page with the encrypted content on success. Else, an - * error value or NULL. + * Return: A page containing the encrypted data on success, else an ERR_PTR() */ struct page *fscrypt_encrypt_page(const struct inode *inode, struct page *page, @@ -234,7 +221,6 @@ struct page *fscrypt_encrypt_page(const struct inode *inode, u64 lblk_num, gfp_t gfp_flags) { - struct fscrypt_ctx *ctx; struct page *ciphertext_page = page; int err; @@ -253,30 +239,20 @@ struct page *fscrypt_encrypt_page(const struct inode *inode, BUG_ON(!PageLocked(page)); - ctx = fscrypt_get_ctx(gfp_flags); - if (IS_ERR(ctx)) - return ERR_CAST(ctx); - /* The encryption operation will require a bounce page. */ - ciphertext_page = fscrypt_alloc_bounce_page(ctx, gfp_flags); - if (IS_ERR(ciphertext_page)) - goto errout; + ciphertext_page = fscrypt_alloc_bounce_page(gfp_flags); + if (!ciphertext_page) + return ERR_PTR(-ENOMEM); - ctx->w.control_page = page; err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num, page, ciphertext_page, len, offs, gfp_flags); if (err) { - ciphertext_page = ERR_PTR(err); - goto errout; + fscrypt_free_bounce_page(ciphertext_page); + return ERR_PTR(err); } SetPagePrivate(ciphertext_page); - set_page_private(ciphertext_page, (unsigned long)ctx); - lock_page(ciphertext_page); - return ciphertext_page; - -errout: - fscrypt_release_ctx(ctx); + set_page_private(ciphertext_page, (unsigned long)page); return ciphertext_page; } EXPORT_SYMBOL(fscrypt_encrypt_page); @@ -355,18 +331,6 @@ const struct dentry_operations fscrypt_d_ops = { .d_revalidate = fscrypt_d_revalidate, }; -void fscrypt_restore_control_page(struct page *page) -{ - struct fscrypt_ctx *ctx; - - ctx = (struct fscrypt_ctx *)page_private(page); - set_page_private(page, (unsigned long)NULL); - ClearPagePrivate(page); - unlock_page(page); - fscrypt_release_ctx(ctx); -} -EXPORT_SYMBOL(fscrypt_restore_control_page); - static void fscrypt_destroy(void) { struct fscrypt_ctx *pos, *n; -- cgit v1.2.3