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From:   Dongliang Mu <dzm91@hust.edu.cn>
To:     Dave Kleikamp <shaggy@kernel.org>
Cc:     Dongliang Mu <mudongliangabcd@gmail.com>,
        syzbot+15342c1aa6a00fb7a438@syzkaller.appspotmail.com,
        jfs-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: [PATCH] fs: jfs: fix shift-out-of-bounds in dbAllocAG
Date:   Thu, 29 Sep 2022 13:44:59 +0800
Message-Id: <20220929054500.488604-1-dzm91@hust.edu.cn>
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From: Dongliang Mu <mudongliangabcd@gmail.com>

Syzbot found a crash : UBSAN: shift-out-of-bounds in dbAllocAG. The
underlying bug is the missing check of bmp->db_agl2size. The field can
be greater than 32 and trigger the shift-out-of-bounds.

Fix this bug by adding a check of bmp->db_agl2size in dbMount since this
field is used in many following functions. Note that, for maintainance,
I reorganzie the error handling code of dbMount.

Reported-by: syzbot+15342c1aa6a00fb7a438@syzkaller.appspotmail.com
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
---
 fs/jfs/jfs_dmap.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 6b838d3ae7c2..4c717f245920 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -155,7 +155,7 @@ int dbMount(struct inode *ipbmap)
 	struct bmap *bmp;
 	struct dbmap_disk *dbmp_le;
 	struct metapage *mp;
-	int i;
+	int i, err;
 
 	/*
 	 * allocate/initialize the in-memory bmap descriptor
@@ -170,8 +170,8 @@ int dbMount(struct inode *ipbmap)
 			   BMAPBLKNO << JFS_SBI(ipbmap->i_sb)->l2nbperpage,
 			   PSIZE, 0);
 	if (mp == NULL) {
-		kfree(bmp);
-		return -EIO;
+		err = -EIO;
+		goto err_kfree_bmp;
 	}
 
 	/* copy the on-disk bmap descriptor to its in-memory version. */
@@ -181,9 +181,8 @@ int dbMount(struct inode *ipbmap)
 	bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
 	bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
 	if (!bmp->db_numag) {
-		release_metapage(mp);
-		kfree(bmp);
-		return -EINVAL;
+		err = -EINVAL;
+		goto err_release_metapage;
 	}
 
 	bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
@@ -194,6 +193,10 @@ int dbMount(struct inode *ipbmap)
 	bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);
 	bmp->db_agstart = le32_to_cpu(dbmp_le->dn_agstart);
 	bmp->db_agl2size = le32_to_cpu(dbmp_le->dn_agl2size);
+	if (bmp->db_agl2size >= 32) {
+		err = -EINVAL;
+		goto err_release_metapage;
+	}
 	for (i = 0; i < MAXAG; i++)
 		bmp->db_agfree[i] = le64_to_cpu(dbmp_le->dn_agfree[i]);
 	bmp->db_agsize = le64_to_cpu(dbmp_le->dn_agsize);
@@ -214,6 +217,12 @@ int dbMount(struct inode *ipbmap)
 	BMAP_LOCK_INIT(bmp);
 
 	return (0);
+
+err_release_metapage:
+	release_metapage(mp);
+err_kfree_bmp:
+	kfree(bmp);
+	return err;
 }
 
 
-- 
2.35.1