From: Oleg Nesterov <oleg@xxxxxxxxxx> Subject: exec: binfmt_misc: don't nullify Node->dentry in kill_node() kill_node() nullifies/checks Node->dentry to avoid double free. This complicates the next changes and this is very confusing: - we do not need to check dentry != NULL under entries_lock, kill_node() is always called under inode_lock(d_inode(root)) and we rely on this inode_lock() anyway, without this lock the MISC_FMT_OPEN_FILE cleanup could race with itself. - if kill_inode() was already called and ->dentry == NULL we should not even try to close e->interp_file. We can change bm_entry_write() to simply check !list_empty(list) before kill_node. Again, we rely on inode_lock(), in particular it saves us from the race with bm_status_write(), another caller of kill_node(). Link: http://lkml.kernel.org/r/20170922143641.GA17210@xxxxxxxxxx Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Ben Woodard <woodard@xxxxxxxxxx> Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> Cc: Jim Foraker <foraker1@xxxxxxxx> Cc: <tdhooge@xxxxxxxx> Cc: Travis Gummels <tgummels@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/binfmt_misc.c | 22 +++++++++------------- 1 file changed, 9 insertions(+), 13 deletions(-) diff -puN fs/binfmt_misc.c~exec-binfmt_misc-dont-nullify-node-dentry-in-kill_node fs/binfmt_misc.c --- a/fs/binfmt_misc.c~exec-binfmt_misc-dont-nullify-node-dentry-in-kill_node +++ a/fs/binfmt_misc.c @@ -603,11 +603,7 @@ static void kill_node(Node *e) struct dentry *dentry; write_lock(&entries_lock); - dentry = e->dentry; - if (dentry) { - list_del_init(&e->list); - e->dentry = NULL; - } + list_del_init(&e->list); write_unlock(&entries_lock); if ((e->flags & MISC_FMT_OPEN_FILE) && e->interp_file) { @@ -615,12 +611,11 @@ static void kill_node(Node *e) e->interp_file = NULL; } - if (dentry) { - drop_nlink(d_inode(dentry)); - d_drop(dentry); - dput(dentry); - simple_release_fs(&bm_mnt, &entry_count); - } + dentry = e->dentry; + drop_nlink(d_inode(dentry)); + d_drop(dentry); + dput(dentry); + simple_release_fs(&bm_mnt, &entry_count); } /* /<entry> */ @@ -665,7 +660,8 @@ static ssize_t bm_entry_write(struct fil root = file_inode(file)->i_sb->s_root; inode_lock(d_inode(root)); - kill_node(e); + if (!list_empty(&e->list)) + kill_node(e); inode_unlock(d_inode(root)); break; @@ -794,7 +790,7 @@ static ssize_t bm_status_write(struct fi inode_lock(d_inode(root)); while (!list_empty(&entries)) - kill_node(list_entry(entries.next, Node, list)); + kill_node(list_first_entry(&entries, Node, list)); inode_unlock(d_inode(root)); break; _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
