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Sun, 15 Dec 2024 18:57:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68EE3C4CEDE; Sun, 15 Dec 2024 18:58:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1734289103; bh=kCPvW5FxPOYga8gMnuTxx4jZhRkpftnsIXUFxGq60Z0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=C5ntpeov+8jzlqBsYyFs3l5HVfXviB9nAAzmvK64xTn1UYiKjw1SB7c0JlaVKBJfS G4XcptzghgKtD1BQkJVfe1RECm3Yl7yGtai5oWP6sH+q4dHej1RwnoS8tga8aIZXEH GVOG+3GrmojLwShFeV8wgrqymn4csMiqrfXErD9klwvBYpIJU8p9eZtnhNQsCSd+Er Upd1Rch8Kw4JHMtW4+celCN3TcIs0W6PzhzqyPRI6rn65f7k0YHvnZJlWZCgmeuAwU 1DKJnhYRR9wpZ/zrq+lDRaTyF/GlFc5f9Y2JApXvWSzz1oKZFXQvXbgYH8j50dwpid KvaqMwEteUZhg== From: cel@kernel.org To: Hugh Dickins , Christian Brauner , Al Viro Cc: , , yukuai3@huawei.com, yangerkun@huaweicloud.com, Chuck Lever Subject: [PATCH v5 3/5] Revert "libfs: fix infinite directory reads for offset dir" Date: Sun, 15 Dec 2024 13:58:14 -0500 Message-ID: <20241215185816.1826975-4-cel@kernel.org> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241215185816.1826975-1-cel@kernel.org> References: <20241215185816.1826975-1-cel@kernel.org> MIME-Version: 1.0 X-Stat-Signature: ytj9remne9oziikxmnhbtwohwpwqfwtg X-Rspam-User: X-Rspamd-Queue-Id: E8655A000A X-Rspamd-Server: rspam08 X-HE-Tag: 1734289065-351266 X-HE-Meta: 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 qiH9Ymik wc8DnumHl18JJvPHRsbCBYqqbTTJTT1wShpcM7nUyfzxDe2WYHlTXGR80rd7XLtgm3WZ4pJNbcm637bbsUXwUIBxTdjaokNoGkug7X7sgImzf5J+Xzi9+eXeMoIiKjGjN6yMBDqH4Yq6IEemSjVs1HibvHIEl/agdtbf8uflFjnY5aWY3Bf1zQCOzXdWgIRXvcCi7E92DH18tvcAm+5UNGbKZxBMfgCaTS8xqzkkWHAXToSvS6vpdVVHx8HK4snOI6LvY X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Chuck Lever The current directory offset allocator (based on mtree_alloc_cyclic) stores the next offset value to return in octx->next_offset. This mechanism typically returns values that increase monotonically over time. Eventually, though, the newly allocated offset value wraps back to a low number (say, 2) which is smaller than other already- allocated offset values. Yu Kuai reports that, after commit 64a7ce76fb90 ("libfs: fix infinite directory reads for offset dir"), if a directory's offset allocator wraps, existing entries are no longer visible via readdir/getdents because offset_readdir() stops listing entries once an entry's offset is larger than octx->next_offset. These entries vanish persistently -- they can be looked up, but will never again appear in readdir(3) output. The reason for this is that the commit treats directory offsets as monotonically increasing integer values rather than opaque cookies, and introduces this comparison: if (dentry2offset(dentry) >= last_index) { On 64-bit platforms, the directory offset value upper bound is 2^63 - 1. Directory offsets will monotonically increase for millions of years without wrapping. On 32-bit platforms, however, LONG_MAX is 2^31 - 1. The allocator can wrap after only a few weeks (at worst). Revert commit 64a7ce76fb90 ("libfs: fix infinite directory reads for offset dir") to prepare for a fix that can work properly on 32-bit systems and might apply to recent LTS kernels where shmem employs the simple_offset mechanism. Reported-by: Yu Kuai Signed-off-by: Chuck Lever --- fs/libfs.c | 35 +++++++++++------------------------ 1 file changed, 11 insertions(+), 24 deletions(-) diff --git a/fs/libfs.c b/fs/libfs.c index 9bcc97ffae48..fdf6ba305112 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -424,14 +424,6 @@ void simple_offset_destroy(struct offset_ctx *octx) mtree_destroy(&octx->mt); } -static int offset_dir_open(struct inode *inode, struct file *file) -{ - struct offset_ctx *ctx = inode->i_op->get_offset_ctx(inode); - - file->private_data = (void *)ctx->next_offset; - return 0; -} - /** * offset_dir_llseek - Advance the read position of a directory descriptor * @file: an open directory whose position is to be updated @@ -445,9 +437,6 @@ static int offset_dir_open(struct inode *inode, struct file *file) */ static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence) { - struct inode *inode = file->f_inode; - struct offset_ctx *ctx = inode->i_op->get_offset_ctx(inode); - switch (whence) { case SEEK_CUR: offset += file->f_pos; @@ -461,8 +450,7 @@ static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence) } /* In this case, ->private_data is protected by f_pos_lock */ - if (!offset) - file->private_data = (void *)ctx->next_offset; + file->private_data = NULL; return vfs_setpos(file, offset, LONG_MAX); } @@ -493,7 +481,7 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) inode->i_ino, fs_umode_to_dtype(inode->i_mode)); } -static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx, long last_index) +static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) { struct offset_ctx *octx = inode->i_op->get_offset_ctx(inode); struct dentry *dentry; @@ -501,21 +489,17 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx, lon while (true) { dentry = offset_find_next(octx, ctx->pos); if (!dentry) - return; - - if (dentry2offset(dentry) >= last_index) { - dput(dentry); - return; - } + return ERR_PTR(-ENOENT); if (!offset_dir_emit(ctx, dentry)) { dput(dentry); - return; + break; } ctx->pos = dentry2offset(dentry) + 1; dput(dentry); } + return NULL; } /** @@ -542,19 +526,22 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx, lon static int offset_readdir(struct file *file, struct dir_context *ctx) { struct dentry *dir = file->f_path.dentry; - long last_index = (long)file->private_data; lockdep_assert_held(&d_inode(dir)->i_rwsem); if (!dir_emit_dots(file, ctx)) return 0; - offset_iterate_dir(d_inode(dir), ctx, last_index); + /* In this case, ->private_data is protected by f_pos_lock */ + if (ctx->pos == DIR_OFFSET_MIN) + file->private_data = NULL; + else if (file->private_data == ERR_PTR(-ENOENT)) + return 0; + file->private_data = offset_iterate_dir(d_inode(dir), ctx); return 0; } const struct file_operations simple_offset_dir_operations = { - .open = offset_dir_open, .llseek = offset_dir_llseek, .iterate_shared = offset_readdir, .read = generic_read_dir,