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Subject[PATCH] udf: limit the maximum number of TD redirections
Date
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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