Subject: [PATCH 2.6.32 09/12] udf: Check component length before reading it

From: Jan Kara <[email-masked]>
Date: Fri, 19 Dec 2014 14:27:55 +0100

commit e237ec37ec154564f8690c5bd1795339955eeef9 upstream.

Check that length specified in a component of a symlink fits in the
input buffer we are reading. Also properly ignore component length for
component types that do not use it. Otherwise we read memory after end
of buffer for corrupted udf image.

Reported-by: Carl Henrik Lunde <[email-masked]>
Signed-off-by: Jan Kara <[email-masked]>
Signed-off-by: Ben Hutchings <[email-masked]>
---
 fs/udf/symlink.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/udf/symlink.c b/fs/udf/symlink.c
index 500c146..c45bb43 100644
--- a/fs/udf/symlink.c
+++ b/fs/udf/symlink.c
@@ -44,14 +44,17 @@ static int udf_pc_to_char(struct super_block *sb, char *from,
 	tolen--;
 	while (elen < fromlen) {
 		pc = (struct pathComponent *)(from + elen);
+		elen += sizeof(struct pathComponent);
 		switch (pc->componentType) {
 		case 1:
 			/*
 			 * Symlink points to some place which should be agreed
  			 * upon between originator and receiver of the media. Ignore.
 			 */
-			if (pc->lengthComponentIdent > 0)
+			if (pc->lengthComponentIdent > 0) {
+				elen += pc->lengthComponentIdent;
 				break;
+			}
 			/* Fall through */
 		case 2:
 			if (tolen == 0)
@@ -76,6 +79,9 @@ static int udf_pc_to_char(struct super_block *sb, char *from,
 			/* that would be . - just ignore */
 			break;
 		case 5:
+			elen += pc->lengthComponentIdent;
+			if (elen > fromlen)
+				return -EIO;
 			comp_len = udf_get_filename(sb, pc->componentIdent,
 						    pc->lengthComponentIdent,
 						    p, tolen);
@@ -87,7 +93,6 @@ static int udf_pc_to_char(struct super_block *sb, char *from,
 			tolen--;
 			break;
 		}
-		elen += sizeof(struct pathComponent) + pc->lengthComponentIdent;
 	}
 	if (p > to + 1)
 		p[-1] = '\0';