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Fri, 20 Dec 2024 15:33:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1734708800; bh=44QvGk8cIKJkG2AbH47kX36uIs9FlMTaiShWTtz/ZcE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EfUEtpDihevl5FaH91uNvj3qNDv+vCgXN/+wQmjpCG+c95edl47dkT2mQSFMPQklp K+JIysQ1B01PYNBuNlda1NkEHbGvmjoclasvpYJQ1dboVZjyLiCpwrPgiWsSSx0U3O TjzlwRlMr9b9qb7iskCxs+FhFpgP0rXHVTKnbKdOT22i5VKYwR6WJh0A1TWex93mT7 NPmCUXC/tb+p6kDt61+M94b++o/yFr7+57PHIaHBJaS/emfM6tCViLuEhn2cc1poi2 qUVbH19l2VoDV1BPh+LHZTenKyKN5BwsH7x2gHw2T8v/O7ER3MZ0Ftv/SZ6ni7GYca SQ0VIffdoEkNw== From: cel@kernel.org To: Hugh Dickins , Christian Brauner , Al Viro Cc: , , yukuai3@huawei.com, yangerkun@huaweicloud.com, Chuck Lever Subject: [PATCH v6 3/5] Revert "libfs: fix infinite directory reads for offset dir" Date: Fri, 20 Dec 2024 10:33:12 -0500 Message-ID: <20241220153314.5237-4-cel@kernel.org> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241220153314.5237-1-cel@kernel.org> References: <20241220153314.5237-1-cel@kernel.org> MIME-Version: 1.0 X-Stat-Signature: xobwbze7id7d61wjiufwgitiffpu1qsa X-Rspamd-Queue-Id: 944A4180012 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1734708777-448357 X-HE-Meta: U2FsdGVkX19uUFvDJUVv6nUKwZcyfrUyb/cqEyhnPrR9YT9o1yNJV6Vl11JcXjfG/3fQE4h/ezFyPU0L8mtQDP2c7buJkJwyQXPVWXGPE6Jt+yy8E+0ploIPfcGakyRezOgkBAuZb5h93eVJZqrLKLeUR2LjyOP7Sb94mUxg4Vq1/ccwLwyXJolozymOvh+JtQFHbWuLlqeRYRYmdBMWsZ78gl+afmArPzgfboyvjJD7EtF4kF+1stFwTjCJSucevSnq+d6pVOdvhyX35XghlHRizPB5MlazAo/klthBT6bXPMUSLPcw6E0OrgDIvlBQ1RGwBA58gKpNORsIL5O4/P6pSx9LdzVdaAtm5oyYKlSuMDhJU7GC7T9TxhATEDxxeiiW8cT0Gtn7TZPIyCA1+tfEIKsHcMOMYtVQSs8kZ8rRq0u+HtNtmZlDX2yRa8nEDDoG3bTtowfLhZs3BZWHmsIDRGY3X4vAc8rEtSMDtP1S4AhSlYqfVlW4PEWGXk6NFkdnFZaRnz0faUv5WiLY5IumKahyP3Z6cxAQZI7qZqsbUXiE5ASXtslzVuzHjmiNu8IfIqRzUG7+xIPW8CtSaRreCj4y1pQ46tWKytNEZhZ9KNcNr/rSRsIo3PJOTQMbw4hPK0Z1Ntpt/iUS5qhCHD9z9KDXwu/6lNbLpCc+L2QHbTN8EFQuWc/jnwxjg1oiItvBfAnP9vsoLYnOr+utU48QyuUGCjNZce4pIPalX32616Bvc8JDEuXMd1UBN7xUNRATAi5pnghrPflQTryEtFhgMwff4B9mSKnVQGlktYKX95cLrQlX+alrwXfbK+oYCy7ZqGbMz3Zt9S7oUK58NKoc7EYUWclHQeFryl20CriSBxtj68V8CIzQrA1/44mCK40b2Nm+VRvGhoJuQTGy9pKcLrdktiyY+nfudml7/oa5u874Dx/h/4FwlGxhO2QHagzEhRi4pEenczuwkv3 4nE3dq02 SWzsSVP/+qE4tSAroWI5/gjWE++wZXykkopAfzn7buCRbY+/4SPb4a42HKh564mF5Y8ZyeeXzRek5yCmHGYBE8oyeWe/+ZTuAL6BVh+dvdSjmYEGP3WtEUNOKpY7FUaoyiboBHMI3LeJeesfxSZVscSp+VKDNtOgKoEGDmbOmQfyC2uSbI41veAoH0wyO4eo0SkUMfihug+rsZNCuhd84cOgoCOvm1oM0+EVXEWoJwSxVAnnnzBTWYm+kiNOPKGz/aBpW 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,