From: Alexey Dobriyan <adobriyan@xxxxxxxxx> Subject: proc: change ->nlink under proc_subdir_lock Currently gluing PDE into global /proc tree is done under lock, but changing ->nlink is not. Additionally struct proc_dir_entry::nlink is not atomic so updates can be lost. Link: http://lkml.kernel.org/r/20190925202436.GA17388@avx2 Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/proc/generic.c | 31 +++++++++++++++---------------- 1 file changed, 15 insertions(+), 16 deletions(-) --- a/fs/proc/generic.c~proc-change-nlink-under-proc_subdir_lock +++ a/fs/proc/generic.c @@ -138,8 +138,12 @@ static int proc_getattr(const struct pat { struct inode *inode = d_inode(path->dentry); struct proc_dir_entry *de = PDE(inode); - if (de && de->nlink) - set_nlink(inode, de->nlink); + if (de) { + nlink_t nlink = READ_ONCE(de->nlink); + if (nlink > 0) { + set_nlink(inode, nlink); + } + } generic_fillattr(inode, stat); return 0; @@ -362,6 +366,7 @@ struct proc_dir_entry *proc_register(str write_unlock(&proc_subdir_lock); goto out_free_inum; } + dir->nlink++; write_unlock(&proc_subdir_lock); return dp; @@ -472,10 +477,7 @@ struct proc_dir_entry *proc_mkdir_data(c ent->data = data; ent->proc_fops = &proc_dir_operations; ent->proc_iops = &proc_dir_inode_operations; - parent->nlink++; ent = proc_register(parent, ent); - if (!ent) - parent->nlink--; } return ent; } @@ -505,10 +507,7 @@ struct proc_dir_entry *proc_create_mount ent->data = NULL; ent->proc_fops = NULL; ent->proc_iops = NULL; - parent->nlink++; ent = proc_register(parent, ent); - if (!ent) - parent->nlink--; } return ent; } @@ -666,8 +665,12 @@ void remove_proc_entry(const char *name, len = strlen(fn); de = pde_subdir_find(parent, fn, len); - if (de) + if (de) { rb_erase(&de->subdir_node, &parent->subdir); + if (S_ISDIR(de->mode)) { + parent->nlink--; + } + } write_unlock(&proc_subdir_lock); if (!de) { WARN(1, "name '%s'\n", name); @@ -676,9 +679,6 @@ void remove_proc_entry(const char *name, proc_entry_rundown(de); - if (S_ISDIR(de->mode)) - parent->nlink--; - de->nlink = 0; WARN(pde_subdir_first(de), "%s: removing non-empty directory '%s/%s', leaking at least '%s'\n", __func__, de->parent->name, de->name, pde_subdir_first(de)->name); @@ -714,13 +714,12 @@ int remove_proc_subtree(const char *name de = next; continue; } - write_unlock(&proc_subdir_lock); - - proc_entry_rundown(de); next = de->parent; if (S_ISDIR(de->mode)) next->nlink--; - de->nlink = 0; + write_unlock(&proc_subdir_lock); + + proc_entry_rundown(de); if (de == root) break; pde_put(de); _
