udf: Check path length when reading symlink

Symlink reading code does not check whether the resulting path fits into
the page provided by the generic code. This isn't as easy as just
checking the symlink size because of various encoding conversions we
perform on path. So we have to check whether there is still enough space
in the buffer on the fly.

CC: stable@vger.kernel.org
Reported-by: Carl Henrik Lunde <chlunde@ping.uio.no>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 26 insertions, 5 deletions

diff --git a/fs/udf/symlink.c b/fs/udf/symlink.c
index c3aa6fa..0f1b3a2 100644
--- a/fs/udf/symlink.c
+++ b/fs/udf/symlink.c
@@ -30,13 +30,16 @@
 #include <linux/buffer_head.h>
 #include "udf_i.h"
 
-static void udf_pc_to_char(struct super_block *sb, unsigned char *from,
-			   int fromlen, unsigned char *to)
+static int udf_pc_to_char(struct super_block *sb, unsigned char *from,
+			  int fromlen, unsigned char *to, int tolen)
 {
 	struct pathComponent *pc;
 	int elen = 0;
+	int comp_len;
 	unsigned char *p = to;
 
+	/* Reserve one byte for terminating \0 */
+	tolen--;
 	while (elen < fromlen) {
 		pc = (struct pathComponent *)(from + elen);
 		switch (pc->componentType) {
@@ -49,22 +52,37 @@ static void udf_pc_to_char(struct super_block *sb, unsigned char *from,
 				break;
 			/* Fall through */
 		case 2:
+			if (tolen == 0)
+				return -ENAMETOOLONG;
 			p = to;
 			*p++ = '/';
+			tolen--;
 			break;
 		case 3:
+			if (tolen < 3)
+				return -ENAMETOOLONG;
 			memcpy(p, "../", 3);
 			p += 3;
+			tolen -= 3;
 			break;
 		case 4:
+			if (tolen < 2)
+				return -ENAMETOOLONG;
 			memcpy(p, "./", 2);
 			p += 2;
+			tolen -= 2;
 			/* that would be . - just ignore */
 			break;
 		case 5:
-			p += udf_get_filename(sb, pc->componentIdent, p,
-					      pc->lengthComponentIdent);
+			comp_len = udf_get_filename(sb, pc->componentIdent,
+						    pc->lengthComponentIdent,
+						    p, tolen);
+			p += comp_len;
+			tolen -= comp_len;
+			if (tolen == 0)
+				return -ENAMETOOLONG;
 			*p++ = '/';
+			tolen--;
 			break;
 		}
 		elen += sizeof(struct pathComponent) + pc->lengthComponentIdent;
@@ -73,6 +91,7 @@ static void udf_pc_to_char(struct super_block *sb, unsigned char *from,
 		p[-1] = '\0';
 	else
 		p[0] = '\0';
+	return 0;
 }
 
 static int udf_symlink_filler(struct file *file, struct page *page)
@@ -108,8 +127,10 @@ static int udf_symlink_filler(struct file *file, struct page *page)
 		symlink = bh->b_data;
 	}
 
-	udf_pc_to_char(inode->i_sb, symlink, inode->i_size, p);
+	err = udf_pc_to_char(inode->i_sb, symlink, inode->i_size, p, PAGE_SIZE);
 	brelse(bh);
+	if (err)
+		goto out_unlock_inode;
 
 	up_read(&iinfo->i_data_sem);
 	SetPageUptodate(page);