[PATCH AUTOSEL 6.10 3/7] f2fs: fix to cover read extent cache access with lock

Sasha Levin
2024-07-30T12:45:25Z

From: Chao Yu <chao@kernel.org>

[ Upstream commit d7409b05a64f212735f0d33f5f1602051a886eab ]

syzbot reports a f2fs bug as below:

BUG: KASAN: slab-use-after-free in sanity_check_extent_cache+0x370/0x410 fs/f2fs/extent_cache.c:46
Read of size 4 at addr ffff8880739ab220 by task syz-executor200/5097

CPU: 0 PID: 5097 Comm: syz-executor200 Not tainted 6.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
print_address_description mm/kasan/report.c:377 [inline]
print_report+0x169/0x550 mm/kasan/report.c:488
kasan_report+0x143/0x180 mm/kasan/report.c:601
sanity_check_extent_cache+0x370/0x410 fs/f2fs/extent_cache.c:46
do_read_inode fs/f2fs/inode.c:509 [inline]
f2fs_iget+0x33e1/0x46e0 fs/f2fs/inode.c:560
f2fs_nfs_get_inode+0x74/0x100 fs/f2fs/super.c:3237
generic_fh_to_dentry+0x9f/0xf0 fs/libfs.c:1413
exportfs_decode_fh_raw+0x152/0x5f0 fs/exportfs/expfs.c:444
exportfs_decode_fh+0x3c/0x80 fs/exportfs/expfs.c:584
do_handle_to_path fs/fhandle.c:155 [inline]
handle_to_path fs/fhandle.c:210 [inline]
do_handle_open+0x495/0x650 fs/fhandle.c:226
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

We missed to cover sanity_check_extent_cache() w/ extent cache lock,
so, below race case may happen, result in use after free issue.

- f2fs_iget
- do_read_inode
- f2fs_init_read_extent_tree
: add largest extent entry in to cache
- shrink
- f2fs_shrink_read_extent_tree
- __shrink_extent_tree
- __detach_extent_node
: drop largest extent entry
- sanity_check_extent_cache
: access et->largest w/o lock

let's refactor sanity_check_extent_cache() to avoid extent cache access
and call it before f2fs_init_read_extent_tree() to fix this issue.

Reported-by: syzbot+74ebe2104433e9dc610d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-f2fs-devel/00000000000009beea061740a531@google.com
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/f2fs/extent_cache.c | 48 +++++++++++++++++-------------------------
fs/f2fs/f2fs.h | 2 +-
fs/f2fs/inode.c | 10 ++++-----
3 files changed, 25 insertions(+), 35 deletions(-)

diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
index 48048fa364276..fd1fc06359eea 100644
--- a/fs/f2fs/extent_cache.c
+++ b/fs/f2fs/extent_cache.c
@@ -19,33 +19,23 @@
#include "node.h"
#include <trace/events/f2fs.h>

-bool sanity_check_extent_cache(struct inode *inode)
+bool sanity_check_extent_cache(struct inode *inode, struct page *ipage)
{
struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
- struct f2fs_inode_info *fi = F2FS_I(inode);
- struct extent_tree *et = fi->extent_tree[EX_READ];
- struct extent_info *ei;
-
- if (!et)
- return true;
+ struct f2fs_extent *i_ext = &F2FS_INODE(ipage)->i_ext;
+ struct extent_info ei;

- ei = &et->largest;
- if (!ei->len)
- return true;
+ get_read_extent_info(&ei, i_ext);

- /* Let's drop, if checkpoint got corrupted. */
- if (is_set_ckpt_flags(sbi, CP_ERROR_FLAG)) {
- ei->len = 0;
- et->largest_updated = true;
+ if (!ei.len)
return true;
- }

- if (!f2fs_is_valid_blkaddr(sbi, ei->blk, DATA_GENERIC_ENHANCE) ||
- !f2fs_is_valid_blkaddr(sbi, ei->blk + ei->len - 1,
+ if (!f2fs_is_valid_blkaddr(sbi, ei.blk, DATA_GENERIC_ENHANCE) ||
+ !f2fs_is_valid_blkaddr(sbi, ei.blk + ei.len - 1,
DATA_GENERIC_ENHANCE)) {
f2fs_warn(sbi, "%s: inode (ino=%lx) extent info [%u, %u, %u] is incorrect, run fsck to fix",
__func__, inode->i_ino,
- ei->blk, ei->fofs, ei->len);
+ ei.blk, ei.fofs, ei.len);
return false;
}
return true;
@@ -394,24 +384,22 @@ void f2fs_init_read_extent_tree(struct inode *inode, struct page *ipage)

if (!__may_extent_tree(inode, EX_READ)) {
/* drop largest read extent */
- if (i_ext && i_ext->len) {
+ if (i_ext->len) {
f2fs_wait_on_page_writeback(ipage, NODE, true, true);
i_ext->len = 0;
set_page_dirty(ipage);
}
- goto out;
+ set_inode_flag(inode, FI_NO_EXTENT);
+ return;
}

et = __grab_extent_tree(inode, EX_READ);

- if (!i_ext || !i_ext->len)
- goto out;
-
get_read_extent_info(&ei, i_ext);

write_lock(&et->lock);
- if (atomic_read(&et->node_cnt))
- goto unlock_out;
+ if (atomic_read(&et->node_cnt) || !ei.len)
+ goto skip;

en = __attach_extent_node(sbi, et, &ei, NULL,
&et->root.rb_root.rb_node, true);
@@ -423,11 +411,13 @@ void f2fs_init_read_extent_tree(struct inode *inode, struct page *ipage)
list_add_tail(&en->list, &eti->extent_list);
spin_unlock(&eti->extent_lock);
}
-unlock_out:
+skip:
+ /* Let's drop, if checkpoint got corrupted. */
+ if (f2fs_cp_error(sbi)) {
+ et->largest.len = 0;
+ et->largest_updated = true;
+ }
write_unlock(&et->lock);
-out:
- if (!F2FS_I(inode)->extent_tree[EX_READ])
- set_inode_flag(inode, FI_NO_EXTENT);
}

void f2fs_init_age_extent_tree(struct inode *inode)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index f463961b497c4..86d4f7b198813 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -4190,7 +4190,7 @@ void f2fs_leave_shrinker(struct f2fs_sb_info *sbi);
/*
* extent_cache.c
*/
-bool sanity_check_extent_cache(struct inode *inode);
+bool sanity_check_extent_cache(struct inode *inode, struct page *ipage);
void f2fs_init_extent_tree(struct inode *inode);
void f2fs_drop_extent_tree(struct inode *inode);
void f2fs_destroy_extent_node(struct inode *inode);
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 33b2778d54525..db6a6c17114e0 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -508,16 +508,16 @@ static int do_read_inode(struct inode *inode)

init_idisk_time(inode);

- /* Need all the flag bits */
- f2fs_init_read_extent_tree(inode, node_page);
- f2fs_init_age_extent_tree(inode);
-
- if (!sanity_check_extent_cache(inode)) {
+ if (!sanity_check_extent_cache(inode, node_page)) {
f2fs_put_page(node_page, 1);
f2fs_handle_error(sbi, ERROR_CORRUPTED_INODE);
return -EFSCORRUPTED;
}

+ /* Need all the flag bits */
+ f2fs_init_read_extent_tree(inode, node_page);
+ f2fs_init_age_extent_tree(inode);
+
f2fs_put_page(node_page, 1);

stat_inc_inline_xattr(inode);
--
2.43.0