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authorOleg Nesterov <oleg@redhat.com>2017-10-03 16:15:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-10-03 17:54:25 -0700
commitbaba1b29731c79d605100087b8f02f9e1cf5a344 (patch)
tree23f11135fccb4464ce80d3f18ed162d7c667e420
parentc2315c187fa0d3ab363fdebe22718170b40473e3 (diff)
downloadlinux-baba1b29731c79d605100087b8f02f9e1cf5a344.tar.bz2
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@redhat.com Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Ben Woodard <woodard@redhat.com> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Jim Foraker <foraker1@llnl.gov> Cc: <tdhooge@llnl.gov> Cc: Travis Gummels <tgummels@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/binfmt_misc.c22
1 files changed, 9 insertions, 13 deletions
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index ce7181ea60fa..6451e7520e05 100644
--- a/fs/binfmt_misc.c
+++ b/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 file *file, const char __user *buffer,
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 file *file, const char __user *buffer,
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;