ext4: fail ext4_iget for root directory if unallocated

If the root directory has an i_links_count of zero, then when the file
system is mounted, then when ext4_fill_super() notices the problem and
tries to call iput() the root directory in the error return path,
ext4_evict_inode() will try to free the inode on disk, before all of
the file system structures are set up, and this will result in an OOPS
caused by a NULL pointer dereference.

This issue has been assigned CVE-2018-1092.

https://bugzilla.kernel.org/show_bug.cgi?id=199179
https://bugzilla.redhat.com/show_bug.cgi?id=1560777

Reported-by: Wen Xu <wen.xu@gatech.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
(cherry picked from commit 8e4b5eae5decd9dfe5a4ee369c22028f90ab4c44)

Orabug: 29048557
CVE: CVE-2018-1092

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>
The current patch borrows EFSBADCRC & EFSCORRUPTED flags from the patch below
6a797d27: ext4: call out CRC and corruption errors with specific error codes

Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0db69ab59cdf2f07094943cd3f19b4cef86c17be..d3ccdf3f2795f5401687f0ce1c721c290d29850f 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3171,4 +3171,7 @@ static inline void ext4_clear_io_unwritten_flag(ext4_io_end_t *io_end)
 
 #endif /* __KERNEL__ */
 
+#define EFSBADCRC      EBADMSG         /* Bad CRC detected */
+#define EFSCORRUPTED   EUCLEAN         /* Filesystem is corrupted */
+
 #endif /* _EXT4_H */

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 52b6edde511bc92593b48108fd54d2016052666a..a71df7f34c3fdc962210f29a0634a08f47cc2f4e 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4156,6 +4156,12 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
                goto bad_inode;
        raw_inode = ext4_raw_inode(&iloc);
 
+       if ((ino == EXT4_ROOT_INO) && (raw_inode->i_links_count == 0)) {
+               EXT4_ERROR_INODE(inode, "root inode unallocated");
+               ret = -EFSCORRUPTED;
+               goto bad_inode;
+       }
+
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
                if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >