[4.2.y-ckt stable] Patch "fat: fix fake_offset handling on error path" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    fat: fix fake_offset handling on error path

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 081e697fe3080f1eb48fa0cef22a5f7618f517c0 Mon Sep 17 00:00:00 2001
From: OGAWA Hirofumi <hirofumi at mail.parknet.co.jp>
Date: Fri, 20 Nov 2015 15:57:15 -0800
Subject: fat: fix fake_offset handling on error path

commit 928a477102c4fc6739883415b66987207e3502f4 upstream.

For the root directory, .  and ..  are faked (using dir_emit_dots()) and
ctx->pos is reset from 2 to 0.

A corrupted root directory could cause fat_get_entry() to fail, but
->iterate() (fat_readdir()) reports progress to the VFS (with ctx->pos
rewound to 0), so any following calls to ->iterate() continue to return
the same entries again and again.

The result is that userspace will never see the end of the directory,
causing e.g.  'ls' to hang in a getdents() loop.

[hirofumi at mail.parknet.co.jp: cleanup and make sure to correct fake_offset]
Reported-by: Vegard Nossum <vegard.nossum at oracle.com>
Tested-by: Vegard Nossum <vegard.nossum at oracle.com>
Signed-off-by: Richard Weinberger <richard.weinberger at gmail.com>
Signed-off-by: OGAWA Hirofumi <hirofumi at mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/fat/dir.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 4afc4d9..8b2127f 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -610,9 +610,9 @@ parse_record:
 		int status = fat_parse_long(inode, &cpos, &bh, &de,
 					    &unicode, &nr_slots);
 		if (status < 0) {
-			ctx->pos = cpos;
+			bh = NULL;
 			ret = status;
-			goto out;
+			goto end_of_dir;
 		} else if (status == PARSE_INVALID)
 			goto record_end;
 		else if (status == PARSE_NOT_LONGNAME)
@@ -654,8 +654,9 @@ parse_record:
 	fill_len = short_len;

 start_filldir:
-	if (!fake_offset)
-		ctx->pos = cpos - (nr_slots + 1) * sizeof(struct msdos_dir_entry);
+	ctx->pos = cpos - (nr_slots + 1) * sizeof(struct msdos_dir_entry);
+	if (fake_offset && ctx->pos < 2)
+		ctx->pos = 2;

 	if (!memcmp(de->name, MSDOS_DOT, MSDOS_NAME)) {
 		if (!dir_emit_dot(file, ctx))
@@ -681,14 +682,19 @@ record_end:
 	fake_offset = 0;
 	ctx->pos = cpos;
 	goto get_new;
+
 end_of_dir:
-	ctx->pos = cpos;
+	if (fake_offset && cpos < 2)
+		ctx->pos = 2;
+	else
+		ctx->pos = cpos;
 fill_failed:
 	brelse(bh);
 	if (unicode)
 		__putname(unicode);
 out:
 	mutex_unlock(&sbi->s_lock);
+
 	return ret;
 }

--
1.9.1