[3.19.y-ckt stable] Patch "btrfs: properly set the termination value of ctx->pos in readdir" has been added to the 3.19.y-ckt tree
Kamal Mostafa
kamal at canonical.com
Wed Mar 9 00:24:40 UTC 2016
This is a note to let you know that I have just added a patch titled
btrfs: properly set the termination value of ctx->pos in readdir
to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue
This patch is scheduled to be released in version 3.19.8-ckt16.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
---8<------------------------------------------------------------
>From a8e106ef672d1f3838e36f170cde577feadf7a9b Mon Sep 17 00:00:00 2001
From: David Sterba <dsterba at suse.com>
Date: Fri, 13 Nov 2015 13:44:28 +0100
Subject: btrfs: properly set the termination value of ctx->pos in readdir
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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commit bc4ef7592f657ae81b017207a1098817126ad4cb upstream.
The value of ctx->pos in the last readdir call is supposed to be set to
INT_MAX due to 32bit compatibility, unless 'pos' is intentially set to a
larger value, then it's LLONG_MAX.
There's a report from PaX SIZE_OVERFLOW plugin that "ctx->pos++"
overflows (https://forums.grsecurity.net/viewtopic.php?f=1&t=4284), on a
64bit arch, where the value is 0x7fffffffffffffff ie. LLONG_MAX before
the increment.
We can get to that situation like that:
* emit all regular readdir entries
* still in the same call to readdir, bump the last pos to INT_MAX
* next call to readdir will not emit any entries, but will reach the
bump code again, finds pos to be INT_MAX and sets it to LLONG_MAX
Normally this is not a problem, but if we call readdir again, we'll find
'pos' set to LLONG_MAX and the unconditional increment will overflow.
The report from Victor at
(http://thread.gmane.org/gmane.comp.file-systems.btrfs/49500) with debugging
print shows that pattern:
Overflow: e
Overflow: 7fffffff
Overflow: 7fffffffffffffff
PAX: size overflow detected in function btrfs_real_readdir
fs/btrfs/inode.c:5760 cicus.935_282 max, count: 9, decl: pos; num: 0;
context: dir_context;
CPU: 0 PID: 2630 Comm: polkitd Not tainted 4.2.3-grsec #1
Hardware name: Gigabyte Technology Co., Ltd. H81ND2H/H81ND2H, BIOS F3 08/11/2015
ffffffff81901608 0000000000000000 ffffffff819015e6 ffffc90004973d48
ffffffff81742f0f 0000000000000007 ffffffff81901608 ffffc90004973d78
ffffffff811cb706 0000000000000000 ffff8800d47359e0 ffffc90004973ed8
Call Trace:
[<ffffffff81742f0f>] dump_stack+0x4c/0x7f
[<ffffffff811cb706>] report_size_overflow+0x36/0x40
[<ffffffff812ef0bc>] btrfs_real_readdir+0x69c/0x6d0
[<ffffffff811dafc8>] iterate_dir+0xa8/0x150
[<ffffffff811e6d8d>] ? __fget_light+0x2d/0x70
[<ffffffff811dba3a>] SyS_getdents+0xba/0x1c0
Overflow: 1a
[<ffffffff811db070>] ? iterate_dir+0x150/0x150
[<ffffffff81749b69>] entry_SYSCALL_64_fastpath+0x12/0x83
The jump from 7fffffff to 7fffffffffffffff happens when new dir entries
are not yet synced and are processed from the delayed list. Then the code
could go to the bump section again even though it might not emit any new
dir entries from the delayed list.
The fix avoids entering the "bump" section again once we've finished
emitting the entries, both for synced and delayed entries.
References: https://forums.grsecurity.net/viewtopic.php?f=1&t=4284
Reported-by: Victor <services at swwu.com>
Signed-off-by: David Sterba <dsterba at suse.com>
Tested-by: Holger Hoffstätte <holger.hoffstaette at googlemail.com>
Signed-off-by: Chris Mason <clm at fb.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
fs/btrfs/delayed-inode.c | 3 ++-
fs/btrfs/delayed-inode.h | 2 +-
fs/btrfs/inode.c | 14 +++++++++++++-
3 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index de4e70f..3784816 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1689,7 +1689,7 @@ int btrfs_should_delete_dir_index(struct list_head *del_list,
*
*/
int btrfs_readdir_delayed_dir_index(struct dir_context *ctx,
- struct list_head *ins_list)
+ struct list_head *ins_list, bool *emitted)
{
struct btrfs_dir_item *di;
struct btrfs_delayed_item *curr, *next;
@@ -1733,6 +1733,7 @@ int btrfs_readdir_delayed_dir_index(struct dir_context *ctx,
if (over)
return 1;
+ *emitted = true;
}
return 0;
}
diff --git a/fs/btrfs/delayed-inode.h b/fs/btrfs/delayed-inode.h
index f70119f..0167853 100644
--- a/fs/btrfs/delayed-inode.h
+++ b/fs/btrfs/delayed-inode.h
@@ -144,7 +144,7 @@ void btrfs_put_delayed_items(struct list_head *ins_list,
int btrfs_should_delete_dir_index(struct list_head *del_list,
u64 index);
int btrfs_readdir_delayed_dir_index(struct dir_context *ctx,
- struct list_head *ins_list);
+ struct list_head *ins_list, bool *emitted);
/* for init */
int __init btrfs_delayed_inode_init(void);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 0f48c7c..b89c8b7 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5447,6 +5447,7 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
char *name_ptr;
int name_len;
int is_curr = 0; /* ctx->pos points to the current index? */
+ bool emitted;
/* FIXME, use a real flag for deciding about the key type */
if (root->fs_info->tree_root == root)
@@ -5475,6 +5476,7 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
if (ret < 0)
goto err;
+ emitted = false;
while (1) {
leaf = path->nodes[0];
slot = path->slots[0];
@@ -5554,6 +5556,7 @@ skip:
if (over)
goto nopos;
+ emitted = true;
di_len = btrfs_dir_name_len(leaf, di) +
btrfs_dir_data_len(leaf, di) + sizeof(*di);
di_cur += di_len;
@@ -5566,11 +5569,20 @@ next:
if (key_type == BTRFS_DIR_INDEX_KEY) {
if (is_curr)
ctx->pos++;
- ret = btrfs_readdir_delayed_dir_index(ctx, &ins_list);
+ ret = btrfs_readdir_delayed_dir_index(ctx, &ins_list, &emitted);
if (ret)
goto nopos;
}
+ /*
+ * If we haven't emitted any dir entry, we must not touch ctx->pos as
+ * it was was set to the termination value in previous call. We assume
+ * that "." and ".." were emitted if we reach this point and set the
+ * termination value as well for an empty directory.
+ */
+ if (ctx->pos > 2 && !emitted)
+ goto nopos;
+
/* Reached end of directory/root. Bump pos past the last item. */
ctx->pos++;
--
2.7.0
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