proc_register() increments the parent directory's link count for every entry it registers, while remove_proc_entry() and remove_proc_subtree() decrement it only when the removed entry is a directory. Regular files thus inflate the parent's count while they exist, and leak one link permanently on every create and remove cycle. For example, /proc/bus/pci/00 with twenty-two device files and no subdirectories reports nlink 24 instead of 2, and SR-IOV VF enable and disable cycles, each creating and removing the VF config space entries under /proc/bus/pci/, inflate the link count of that directory without bound. Before commit e06689bf5701 ("proc: change ->nlink under proc_subdir_lock"), the increment lived in proc_mkdir_data() and proc_create_mount_point(), and was therefore applied only to directories. Moving it into proc_register() to bring it under proc_subdir_lock dropped the S_ISDIR check. Thus, move the nlink accounting into pde_subdir_insert() and pde_erase(), only updating it for directories in both, so the link count is always changed together with the directory entry itself. Fixes: e06689bf5701 ("proc: change ->nlink under proc_subdir_lock") Cc: stable@vger.kernel.org # v5.5+ Signed-off-by: Krzysztof Wilczyński --- Changes in v2: https://lore.kernel.org/linux-fsdevel/20260612153031.536525-1-kwilczynski@kernel.org/ - Moved the nlink accounting into pde_subdir_insert() and pde_erase() instead of adding a check in proc_register(), as suggested by Alexey Dobriyan. fs/proc/generic.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/fs/proc/generic.c b/fs/proc/generic.c index 8bb81e58c9d8..32b6b0f97967 100644 --- a/fs/proc/generic.c +++ b/fs/proc/generic.c @@ -112,6 +112,8 @@ static bool pde_subdir_insert(struct proc_dir_entry *dir, /* Add new node and rebalance tree. */ rb_link_node(&de->subdir_node, parent, new); rb_insert_color(&de->subdir_node, root); + if (S_ISDIR(de->mode)) + dir->nlink++; return true; } @@ -404,7 +406,6 @@ struct proc_dir_entry *proc_register(struct proc_dir_entry *dir, write_unlock(&proc_subdir_lock); goto out_free_inum; } - dir->nlink++; write_unlock(&proc_subdir_lock); return dp; @@ -702,6 +703,8 @@ static void pde_erase(struct proc_dir_entry *pde, struct proc_dir_entry *parent) { rb_erase(&pde->subdir_node, &parent->subdir); RB_CLEAR_NODE(&pde->subdir_node); + if (S_ISDIR(pde->mode)) + parent->nlink--; } /* @@ -727,8 +730,6 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent) de = NULL; } else { pde_erase(de, parent); - if (S_ISDIR(de->mode)) - parent->nlink--; } } write_unlock(&proc_subdir_lock); @@ -787,8 +788,6 @@ int remove_proc_subtree(const char *name, struct proc_dir_entry *parent) continue; } next = de->parent; - if (S_ISDIR(de->mode)) - next->nlink--; write_unlock(&proc_subdir_lock); proc_entry_rundown(de); -- 2.54.0