linux-kernel - [PATCH] udf: limit the maximum number of TD redirections

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Date:	Thu, 10 Dec 2015 17:13:41 +0100
From:	Vegard Nossum <vegard.nossum@...cle.com>
To:	Jan Kara <jack@...e.com>
Cc:	linux-kernel@...r.kernel.org, quentin.casasnovas@...cle.com,
	Vegard Nossum <vegard.nossum@...cle.com>
Subject: [PATCH] udf: limit the maximum number of TD redirections

Filesystem fuzzing revealed that we could get stuck in the
udf_process_sequence() loop.

The maximum limit was chosen arbitrarily but fixes the problem I saw.
---
 fs/udf/super.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git fs/udf/super.c fs/udf/super.c
index 81155b9..fd45537 100644
--- fs/udf/super.c
+++ fs/udf/super.c
@@ -1586,6 +1586,13 @@ static void udf_load_logicalvolint(struct super_block *sb, struct kernel_extent_
 }
 
 /*
+ * Maximum number of Terminating Descriptor redirections. The chosen number is
+ * arbitrary - just that we hopefully don't limit any real use of rewritten
+ * inode on write-once media but avoid looping for too long on corrupted media.
+ */
+#define UDF_MAX_TD_NESTING 64
+
+/*
  * Process a main/reserve volume descriptor sequence.
  *   @block		First block of first extent of the sequence.
  *   @lastblock		Lastblock of first extent of the sequence.
@@ -1609,6 +1616,7 @@ static noinline int udf_process_sequence(
 	uint16_t ident;
 	long next_s = 0, next_e = 0;
 	int ret;
+	unsigned int indirections = 0;
 
 	memset(vds, 0, sizeof(struct udf_vds_record) * VDS_POS_LENGTH);
 
@@ -1679,6 +1687,12 @@ static noinline int udf_process_sequence(
 			}
 			break;
 		case TAG_IDENT_TD: /* ISO 13346 3/10.9 */
+			if (++indirections > UDF_MAX_TD_NESTING) {
+				udf_err(sb, "too many TDs (max %u supported)\n", UDF_MAX_TD_NESTING);
+				brelse(bh);
+				return -EIO;
+			}
+
 			vds[VDS_POS_TERMINATING_DESC].block = block;
 			if (next_e) {
 				block = next_s;
-- 
1.9.1

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