fs/minix: don't allow getting deleted inodes

If an inode has no links, we need to mark it bad rather than allowing it
to be accessed.  This avoids WARNINGs in inc_nlink() and drop_nlink() when
doing directory operations on a fuzzed filesystem.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+a9ac3de1b5de5fb10efc@syzkaller.appspotmail.com
Reported-by: syzbot+df958cf5688a96ad3287@syzkaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Qiujun Huang <anenbupt@gmail.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200628060846.682158-3-ebiggers@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/minix/inode.c b/fs/minix/inode.c
index 7cb5fd38eb149ffebd76aa68e61990cbf52820c8..2bca95abe8f49d1d632c115783720fc2edadfda3 100644 (file)
--- a/fs/minix/inode.c
+++ b/fs/minix/inode.c
@@ -468,6 +468,13 @@ static struct inode *V1_minix_iget(struct inode *inode)
                iget_failed(inode);
                return ERR_PTR(-EIO);
        }
+       if (raw_inode->i_nlinks == 0) {
+               printk("MINIX-fs: deleted inode referenced: %lu\n",
+                      inode->i_ino);
+               brelse(bh);
+               iget_failed(inode);
+               return ERR_PTR(-ESTALE);
+       }
        inode->i_mode = raw_inode->i_mode;
        i_uid_write(inode, raw_inode->i_uid);
        i_gid_write(inode, raw_inode->i_gid);
@@ -501,6 +508,13 @@ static struct inode *V2_minix_iget(struct inode *inode)
                iget_failed(inode);
                return ERR_PTR(-EIO);
        }
+       if (raw_inode->i_nlinks == 0) {
+               printk("MINIX-fs: deleted inode referenced: %lu\n",
+                      inode->i_ino);
+               brelse(bh);
+               iget_failed(inode);
+               return ERR_PTR(-ESTALE);
+       }
        inode->i_mode = raw_inode->i_mode;
        i_uid_write(inode, raw_inode->i_uid);
        i_gid_write(inode, raw_inode->i_gid);