From: David Howells dhowells@redhat.com
[ Upstream commit 5e0b17b026eb7c6de9baa9b0d45a51b05f05abe1 ]
If an error occurs during the construction of an afs superblock, it's possible that an error occurs after a superblock is created, but before we've created the root dentry. If the superblock has a dynamic root (ie. what's normally mounted on /afs), the afs_kill_super() will call afs_dynroot_depopulate() to unpin any created dentries - but this will oops if the root hasn't been created yet.
Fix this by skipping that bit of code if there is no root dentry.
This leads to an oops looking like:
general protection fault, ... KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f] ... RIP: 0010:afs_dynroot_depopulate+0x25f/0x529 fs/afs/dynroot.c:385 ... Call Trace: afs_kill_super+0x13b/0x180 fs/afs/super.c:535 deactivate_locked_super+0x94/0x160 fs/super.c:335 afs_get_tree+0x1124/0x1460 fs/afs/super.c:598 vfs_get_tree+0x89/0x2f0 fs/super.c:1547 do_new_mount fs/namespace.c:2875 [inline] path_mount+0x1387/0x2070 fs/namespace.c:3192 do_mount fs/namespace.c:3205 [inline] __do_sys_mount fs/namespace.c:3413 [inline] __se_sys_mount fs/namespace.c:3390 [inline] __x64_sys_mount+0x27f/0x300 fs/namespace.c:3390 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9
which is oopsing on this line:
inode_lock(root->d_inode);
presumably because sb->s_root was NULL.
Fixes: 0da0b7fd73e4 ("afs: Display manually added cells in dynamic root mount") Reported-by: syzbot+c1eff8205244ae7e11a6@syzkaller.appspotmail.com Signed-off-by: David Howells dhowells@redhat.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/afs/dynroot.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-)
diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c index b79879aacc02e..7b784af604fd9 100644 --- a/fs/afs/dynroot.c +++ b/fs/afs/dynroot.c @@ -382,15 +382,17 @@ void afs_dynroot_depopulate(struct super_block *sb) net->dynroot_sb = NULL; mutex_unlock(&net->proc_cells_lock);
- inode_lock(root->d_inode); - - /* Remove all the pins for dirs created for manually added cells */ - list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) { - if (subdir->d_fsdata) { - subdir->d_fsdata = NULL; - dput(subdir); + if (root) { + inode_lock(root->d_inode); + + /* Remove all the pins for dirs created for manually added cells */ + list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) { + if (subdir->d_fsdata) { + subdir->d_fsdata = NULL; + dput(subdir); + } } - }
- inode_unlock(root->d_inode); + inode_unlock(root->d_inode); + } }