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From:   Rustam Kovhaev <rkovhaev@gmail.com>
To:     anton@tuxera.com, linux-ntfs-dev@lists.sourceforge.net
Cc:     linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org,
        Rustam Kovhaev <rkovhaev@gmail.com>
Subject: [PATCH] ntfs: move check for valid resident attribute offset and length
Date:   Sun, 14 Feb 2021 14:12:47 -0800
Message-Id: <20210214221247.621431-1-rkovhaev@gmail.com>
MIME-Version: 1.0
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we should check for valid resident atribute offset and length before
loading STANDARD_INFORMATION attribute in ntfs_read_locked_inode()
let's make that check a bit earlier in the same function to avoid
use-after-free bug

Reported-and-tested-by: syzbot+c584225dabdea2f71969@syzkaller.appspotmail.com
Signed-off-by: Rustam Kovhaev <rkovhaev@gmail.com>
Link: https://syzkaller.appspot.com/bug?extid=c584225dabdea2f71969
---
 fs/ntfs/inode.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
index f7e4cbc26eaf..70745aea5106 100644
--- a/fs/ntfs/inode.c
+++ b/fs/ntfs/inode.c
@@ -629,6 +629,13 @@ static int ntfs_read_locked_inode(struct inode *vi)
 	}
 	a = ctx->attr;
 	/* Get the standard information attribute value. */
+	if ((u8 *)a + le16_to_cpu(a->data.resident.value_offset)
+			+ le32_to_cpu(
+			a->data.resident.value_length) >
+			(u8 *)ctx->mrec + vol->mft_record_size) {
+		ntfs_error(vi->i_sb, "Corrupt attribute list in inode.");
+		goto unm_err_out;
+	}
 	si = (STANDARD_INFORMATION*)((u8*)a +
 			le16_to_cpu(a->data.resident.value_offset));
 
@@ -731,14 +738,6 @@ static int ntfs_read_locked_inode(struct inode *vi)
 				goto unm_err_out;
 			}
 		} else /* if (!a->non_resident) */ {
-			if ((u8*)a + le16_to_cpu(a->data.resident.value_offset)
-					+ le32_to_cpu(
-					a->data.resident.value_length) >
-					(u8*)ctx->mrec + vol->mft_record_size) {
-				ntfs_error(vi->i_sb, "Corrupt attribute list "
-						"in inode.");
-				goto unm_err_out;
-			}
 			/* Now copy the attribute list. */
 			memcpy(ni->attr_list, (u8*)a + le16_to_cpu(
 					a->data.resident.value_offset),
-- 
2.30.0