ext4: check for directory entries too close to block end

commit 109ba779d6cca2d519c5dd624a3276d03e21948e upstream.

ext4_check_dir_entry() currently does not catch a case when a directory
entry ends so close to the block end that the header of the next
directory entry would not fit in the remaining space. This can lead to
directory iteration code trying to access address beyond end of current
buffer head leading to oops.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20191202170213.4761-3-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index 46d5c40f2835fec84ec26620113231fb619644b7..d947c5e439cf209170c827a13a8d07317f3b0aac 100644 (file)
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -77,6 +77,11 @@ int __ext4_check_dir_entry(const char *function, unsigned int line,
                error_msg = "rec_len is too small for name_len";
        else if (unlikely(((char *) de - buf) + rlen > size))
                error_msg = "directory entry overrun";
+       else if (unlikely(((char *) de - buf) + rlen >
+                         size - EXT4_DIR_REC_LEN(1) &&
+                         ((char *) de - buf) + rlen != size)) {
+               error_msg = "directory entry too close to block end";
+       }
        else if (unlikely(le32_to_cpu(de->inode) >
                        le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count)))
                error_msg = "inode out of bounds";