6.12-stable review patch. If anyone has any objections, please let me know.
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From: Chuck Lever chuck.lever@oracle.com
commit b662d858131da9a8a14e68661656989b14dbf113 upstream.
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 yukuai3@huawei.com 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 yukuai3@huawei.com Signed-off-by: Chuck Lever chuck.lever@oracle.com Link: https://lore.kernel.org/r/20241228175522.1854234-4-cel@kernel.org Reviewed-by: Yang Erkun yangerkun@huawei.com Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/libfs.c | 35 +++++++++++------------------------ 1 file changed, 11 insertions(+), 24 deletions(-)
--- a/fs/libfs.c +++ b/fs/libfs.c @@ -418,14 +418,6 @@ void simple_offset_destroy(struct offset 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 @@ -439,9 +431,6 @@ static int offset_dir_open(struct inode */ 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; @@ -455,8 +444,7 @@ static loff_t offset_dir_llseek(struct f }
/* 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); }
@@ -487,7 +475,7 @@ static bool offset_dir_emit(struct dir_c 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; @@ -495,21 +483,17 @@ static void offset_iterate_dir(struct in 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; }
/** @@ -536,19 +520,22 @@ static void offset_iterate_dir(struct in 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,