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Date: Mon, 14 Aug 2023 15:43:51 +0800
From: Baokun Li <libaokun1@...wei.com>
To: <linux-ext4@...r.kernel.org>
CC: <tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>,
<ritesh.list@...il.com>, <linux-kernel@...r.kernel.org>,
<yi.zhang@...wei.com>, <yangerkun@...wei.com>,
<yukuai3@...wei.com>, <libaokun1@...wei.com>,
Yikebaer Aizezi <yikebaer61@...il.com>
Subject: [PATCH] ext4: fix slab-use-after-free in ext4_es_insert_extent()
Yikebaer reported an issue:
==================================================================
BUG: KASAN: slab-use-after-free in ext4_es_insert_extent+0xc68/0xcb0
fs/ext4/extents_status.c:894
Read of size 4 at addr ffff888112ecc1a4 by task syz-executor/8438
CPU: 1 PID: 8438 Comm: syz-executor Not tainted 6.5.0-rc5 #1
Call Trace:
[...]
kasan_report+0xba/0xf0 mm/kasan/report.c:588
ext4_es_insert_extent+0xc68/0xcb0 fs/ext4/extents_status.c:894
ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680
ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462
ext4_zero_range fs/ext4/extents.c:4622 [inline]
ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721
[...]
Allocated by task 8438:
[...]
kmem_cache_zalloc include/linux/slab.h:693 [inline]
__es_alloc_extent fs/ext4/extents_status.c:469 [inline]
ext4_es_insert_extent+0x672/0xcb0 fs/ext4/extents_status.c:873
ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680
ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462
ext4_zero_range fs/ext4/extents.c:4622 [inline]
ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721
[...]
Freed by task 8438:
[...]
kmem_cache_free+0xec/0x490 mm/slub.c:3823
ext4_es_try_to_merge_right fs/ext4/extents_status.c:593 [inline]
__es_insert_extent+0x9f4/0x1440 fs/ext4/extents_status.c:802
ext4_es_insert_extent+0x2ca/0xcb0 fs/ext4/extents_status.c:882
ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680
ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462
ext4_zero_range fs/ext4/extents.c:4622 [inline]
ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721
[...]
==================================================================
The flow of issue triggering is as follows:
1. remove es
raw es es removed es1
|-------------------| -> |----|.......|------|
2. insert es
es insert es1 merge with es es1 merge with es and free es1
|----|.......|------| -> |------------|------| -> |-------------------|
es merges with newes, then merges with es1, frees es1, then determines
if es1->es_len is 0 and triggers a UAF.
The code flow is as follows:
ext4_es_insert_extent
es1 = __es_alloc_extent(true);
es2 = __es_alloc_extent(true);
__es_remove_extent(inode, lblk, end, NULL, es1)
__es_insert_extent(inode, &newes, es1) ---> insert es1 to es tree
__es_insert_extent(inode, &newes, es2)
ext4_es_try_to_merge_right
ext4_es_free_extent(inode, es1) ---> es1 is freed
if (es1 && !es1->es_len)
// Trigger UAF by determining if es1 is used.
We determine whether es1 or es2 is used immediately after calling
__es_remove_extent() or __es_insert_extent() to avoid triggering a
UAF if es1 or es2 is freed.
Reported-by: Yikebaer Aizezi <yikebaer61@...il.com>
Closes: https://lore.kernel.org/lkml/CALcu4raD4h9coiyEBL4Bm0zjDwxC2CyPiTwsP3zFuhot6y9Beg@mail.gmail.com
Fixes: 2a69c450083d ("ext4: using nofail preallocation in ext4_es_insert_extent()")
Signed-off-by: Baokun Li <libaokun1@...wei.com>
---
fs/ext4/extents_status.c | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 9b5b8951afb4..cceac517265f 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -878,23 +878,21 @@ void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
err1 = __es_remove_extent(inode, lblk, end, NULL, es1);
if (err1 != 0)
goto error;
+ if (es1 && !es1->es_len)
+ __es_free_extent(es1);
err2 = __es_insert_extent(inode, &newes, es2);
if (err2 == -ENOMEM && !ext4_es_must_keep(&newes))
err2 = 0;
if (err2 != 0)
goto error;
+ if (es2 && !es2->es_len)
+ __es_free_extent(es2);
if (sbi->s_cluster_ratio > 1 && test_opt(inode->i_sb, DELALLOC) &&
(status & EXTENT_STATUS_WRITTEN ||
status & EXTENT_STATUS_UNWRITTEN))
__revise_pending(inode, lblk, len);
-
- /* es is pre-allocated but not used, free it. */
- if (es1 && !es1->es_len)
- __es_free_extent(es1);
- if (es2 && !es2->es_len)
- __es_free_extent(es2);
error:
write_unlock(&EXT4_I(inode)->i_es_lock);
if (err1 || err2)
@@ -2047,19 +2045,17 @@ void ext4_es_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk,
err1 = __es_remove_extent(inode, lblk, lblk, NULL, es1);
if (err1 != 0)
goto error;
+ if (es1 && !es1->es_len)
+ __es_free_extent(es1);
err2 = __es_insert_extent(inode, &newes, es2);
if (err2 != 0)
goto error;
+ if (es2 && !es2->es_len)
+ __es_free_extent(es2);
if (allocated)
__insert_pending(inode, lblk);
-
- /* es is pre-allocated but not used, free it. */
- if (es1 && !es1->es_len)
- __es_free_extent(es1);
- if (es2 && !es2->es_len)
- __es_free_extent(es2);
error:
write_unlock(&EXT4_I(inode)->i_es_lock);
if (err1 || err2)
--
2.31.1
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