linux-kernel - [PATCH 3.2 21/87] udf: limit the maximum number of indirect extents in a row

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Message-ID: <lsq.1454975631.78308899@decadent.org.uk>
Date:	Mon, 08 Feb 2016 23:53:51 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Quentin Casasnovas" <quentin.casasnovas@...cle.com>,
	"Vegard Nossum" <vegard.nossum@...cle.com>,
	"Jan Kara" <jack@...e.com>, "Jan Kara" <jack@...e.cz>
Subject: [PATCH 3.2 21/87] udf: limit the maximum number of indirect
 extents in a row

3.2.77-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Vegard Nossum <vegard.nossum@...cle.com>

commit b0918d9f476a8434b055e362b83fa4fd1d462c3f upstream.

udf_next_aext() just follows extent pointers while extents are marked as
indirect. This can loop forever for corrupted filesystem. Limit number
the of indirect extents we are willing to follow in a row.

[JK: Updated changelog, limit, style]

Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
Cc: Jan Kara <jack@...e.com>
Cc: Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/udf/inode.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -1975,14 +1975,29 @@ void udf_write_aext(struct inode *inode,
 		epos->offset += adsize;
 }
 
+/*
+ * Only 1 indirect extent in a row really makes sense but allow upto 16 in case
+ * someone does some weird stuff.
+ */
+#define UDF_MAX_INDIR_EXTS 16
+
 int8_t udf_next_aext(struct inode *inode, struct extent_position *epos,
 		     struct kernel_lb_addr *eloc, uint32_t *elen, int inc)
 {
 	int8_t etype;
+	unsigned int indirections = 0;
 
 	while ((etype = udf_current_aext(inode, epos, eloc, elen, inc)) ==
 	       (EXT_NEXT_EXTENT_ALLOCDECS >> 30)) {
 		int block;
+
+		if (++indirections > UDF_MAX_INDIR_EXTS) {
+			udf_err(inode->i_sb,
+				"too many indirect extents in inode %lu\n",
+				inode->i_ino);
+			return -1;
+		}
+
 		epos->block = *eloc;
 		epos->offset = sizeof(struct allocExtDesc);
 		brelse(epos->bh);