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.
