On Tue, May 30, 2023 at 1:26 AM Christian Brauner <brauner@xxxxxxxxxx> wrote: > > On Sun, May 28, 2023 at 11:44:22AM -0700, Prince Kumar Maurya wrote: > > sb_getblk(inode->i_sb, parent) return a null ptr and taking lock on > > that leads to the null-ptr-deref bug. > > > > Reported-by: syzbot+aad58150cbc64ba41bdc@xxxxxxxxxxxxxxxxxxxxxxxxx > > Closes: https://syzkaller.appspot.com/bug?extid=aad58150cbc64ba41bdc > > Signed-off-by: Prince Kumar Maurya <princekumarmaurya06@xxxxxxxxx> > > --- > > Change since v2: Updated subject and added Reported-by and closes tags. > > > > fs/sysv/itree.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/fs/sysv/itree.c b/fs/sysv/itree.c > > index b22764fe669c..3a6b66e719fd 100644 > > --- a/fs/sysv/itree.c > > +++ b/fs/sysv/itree.c > > @@ -145,6 +145,8 @@ static int alloc_branch(struct inode *inode, > > */ > > parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key); > > bh = sb_getblk(inode->i_sb, parent); > > + if (!bh) > > + break; > > When you break here you'll hit: > > /* Allocation failed, free what we already allocated */ > for (i = 1; i < n; i++) > bforget(branch[i].bh); > for (i = 0; i < n; i++) > sysv_free_block(inode->i_sb, branch[i].key); > > below. The cleanup paths were coded in the assumption that sb_getblk() > can't fail. So bforget() can assume that branch[i].bh has been allocated > and set up. So that bforget(branch[i].bh) is your next pending NULL > deref afaict. I doubt that would happen. There is a break above as well, before we do sb_getblk(). /* Allocate the next block */ branch[n].key = sysv_new_block(inode->i_sb); if (!branch[n].key) break; The clean up code path runs till i is less than n not equal to n which would have caused the problem.
