• yangerkun's avatar
    libfs: fix infinite directory reads for offset dir · 64a7ce76
    yangerkun authored
    After we switch tmpfs dir operations from simple_dir_operations to
    simple_offset_dir_operations, every rename happened will fill new dentry
    to dest dir's maple tree(&SHMEM_I(inode)->dir_offsets->mt) with a free
    key starting with octx->newx_offset, and then set newx_offset equals to
    free key + 1. This will lead to infinite readdir combine with rename
    happened at the same time, which fail generic/736 in xfstests(detail show
    as below).
    
    1. create 5000 files(1 2 3...) under one dir
    2. call readdir(man 3 readdir) once, and get one entry
    3. rename(entry, "TEMPFILE"), then rename("TEMPFILE", entry)
    4. loop 2~3, until readdir return nothing or we loop too many
       times(tmpfs break test with the second condition)
    
    We choose the same logic what commit 9b378f6a ("btrfs: fix infinite
    directory reads") to fix it, record the last_index when we open dir, and
    do not emit the entry which index >= last_index. The file->private_data
    now used in offset dir can use directly to do this, and we also update
    the last_index when we llseek the dir file.
    
    Fixes: a2e45955 ("shmem: stable directory offsets")
    Signed-off-by: default avataryangerkun <yangerkun@huawei.com>
    Link: https://lore.kernel.org/r/20240731043835.1828697-1-yangerkun@huawei.comReviewed-by: default avatarChuck Lever <chuck.lever@oracle.com>
    [brauner: only update last_index after seek when offset is zero like Jan suggested]
    Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
    64a7ce76
libfs.c 59.3 KB