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Sat, 28 Dec 2024 17:54:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E53DC4CEDD; Sat, 28 Dec 2024 17:55:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1735408531; bh=44QvGk8cIKJkG2AbH47kX36uIs9FlMTaiShWTtz/ZcE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aGHkO4sy4HrHvpB8SLIsBftKGlob3Y95jIV20+LqDjkuubgCgBp8qFAcAK5Fyj8G7 brz14rgKpeBEykZnI3EHT6iMSv2V5q/3SB7jCob0Bo64VO5FG1UmkL9Mq8mBRdnslm LTd6np81J77a2AJ2+9DlXJSAQiKQehAT/UxsopL35XOJ4iCJD7gyfwKJpfLq2NUMX3 /EdIhLT6f2fKRwpfPRC8USHkCUXZoI92E6Oj/VKi/9iAg5E0qJ5QQoEo/CU5PNtoIy CYqin619Ts4VWpGorEiJiKrlXr8Aac9zFI+VLdJr7zTo8JrOSijNrppBVh9usbkXTL BWQ+I5KvQXstg== From: cel@kernel.org To: Hugh Dickins , Christian Brauner , Al Viro Cc: , , yukuai3@huawei.com, yangerkun@huaweicloud.com, Liam.Howlett@oracle.com, Chuck Lever Subject: [PATCH v7 3/5] Revert "libfs: fix infinite directory reads for offset dir" Date: Sat, 28 Dec 2024 12:55:19 -0500 Message-ID: <20241228175522.1854234-4-cel@kernel.org> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241228175522.1854234-1-cel@kernel.org> References: <20241228175522.1854234-1-cel@kernel.org> MIME-Version: 1.0 X-Rspamd-Queue-Id: DFC711C0009 X-Stat-Signature: 3o6riq4e696rnw34pocw1i7rx58ochue X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1735408446-699459 X-HE-Meta: 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 wqAMMeWG UbjNWi0bvRK6ik2WUzbc3+7NyKbHZs9Mh8ThylisWD2Dsirp6tdePjypBk8qM+AnY2r8I0rM870tqTIhbN1jI0LyabLMWg3B+NDxaqhkOv/y2DAkgOVLl8Hxye9hYvFbtoLeav5eVwPavJNS+BcfhNJmkF2LlBpag3x+TrGa8dzMtHy56EztURh85scFMeJ7nOnd8rPmSP55/vPx1FHk3x2bSVm0TNah7HlnHZ2QWOuMJDR57ZHKmucMXUdz04h9/HXE6 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 8380d9314ebd..8c9364a0174c 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -422,14 +422,6 @@ 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 @@ -443,9 +435,6 @@ 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; @@ -459,8 +448,7 @@ 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); } @@ -491,7 +479,7 @@ 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; @@ -499,21 +487,17 @@ 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; } /** @@ -540,19 +524,22 @@ 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,