From 109ba779d6cca2d519c5dd624a3276d03e21948e Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Mon, 2 Dec 2019 18:02:13 +0100
Subject: [PATCH] ext4: check for directory entries too close to block end
Git-commit: 109ba779d6cca2d519c5dd624a3276d03e21948e
Patch-mainline: v5.5-rc3
References: bsc#1163861

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>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/ext4/dir.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index 9fdd2b269d61..6305d5ec25af 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -81,6 +81,11 @@ 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";
-- 
2.16.4