1 files changed, 30 insertions, 2 deletions

diff --git a/fs/udf/dir.c b/fs/udf/dir.c
index 70abdfad2df1..42e3e551fa4c 100644
--- a/fs/udf/dir.c
+++ b/fs/udf/dir.c
@@ -31,6 +31,7 @@
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/bio.h>
+#include <linux/iversion.h>
 
 #include "udf_i.h"
 #include "udf_sb.h"
@@ -43,7 +44,7 @@ static int udf_readdir(struct file *file, struct dir_context *ctx)
 	struct fileIdentDesc *fi = NULL;
 	struct fileIdentDesc cfi;
 	udf_pblk_t block, iblock;
-	loff_t nf_pos;
+	loff_t nf_pos, emit_pos = 0;
 	int flen;
 	unsigned char *fname = NULL, *copy_name = NULL;
 	unsigned char *nameptr;
@@ -57,6 +58,7 @@ static int udf_readdir(struct file *file, struct dir_context *ctx)
 	int i, num, ret = 0;
 	struct extent_position epos = { NULL, 0, {0, 0} };
 	struct super_block *sb = dir->i_sb;
+	bool pos_valid = false;
 
 	if (ctx->pos == 0) {
 		if (!dir_emit_dot(file, ctx))
@@ -67,6 +69,21 @@ static int udf_readdir(struct file *file, struct dir_context *ctx)
 	if (nf_pos >= size)
 		goto out;
 
+	/*
+	 * Something changed since last readdir (either lseek was called or dir
+	 * changed)?  We need to verify the position correctly points at the
+	 * beginning of some dir entry so that the directory parsing code does
+	 * not get confused. Since UDF does not have any reliable way of
+	 * identifying beginning of dir entry (names are under user control),
+	 * we need to scan the directory from the beginning.
+	 */
+	if (!inode_eq_iversion(dir, file->f_version)) {
+		emit_pos = nf_pos;
+		nf_pos = 0;
+	} else {
+		pos_valid = true;
+	}
+
 	fname = kmalloc(UDF_NAME_LEN, GFP_NOFS);
 	if (!fname) {
 		ret = -ENOMEM;
@@ -122,13 +139,21 @@ static int udf_readdir(struct file *file, struct dir_context *ctx)
 
 	while (nf_pos < size) {
 		struct kernel_lb_addr tloc;
+		loff_t cur_pos = nf_pos;
 
-		ctx->pos = (nf_pos >> 2) + 1;
+		/* Update file position only if we got past the current one */
+		if (nf_pos >= emit_pos) {
+			ctx->pos = (nf_pos >> 2) + 1;
+			pos_valid = true;
+		}
 
 		fi = udf_fileident_read(dir, &nf_pos, &fibh, &cfi, &epos, &eloc,
 					&elen, &offset);
 		if (!fi)
 			goto out;
+		/* Still not at offset where user asked us to read from? */
+		if (cur_pos < emit_pos)
+			continue;
 
 		liu = le16_to_cpu(cfi.lengthOfImpUse);
 		lfi = cfi.lengthFileIdent;
@@ -186,8 +211,11 @@ static int udf_readdir(struct file *file, struct dir_context *ctx)
 	} /* end while */
 
 	ctx->pos = (nf_pos >> 2) + 1;
+	pos_valid = true;
 
 out:
+	if (pos_valid)
+		file->f_version = inode_query_iversion(dir);
 	if (fibh.sbh != fibh.ebh)
 		brelse(fibh.ebh);
 	brelse(fibh.sbh);