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linux/fs/9p
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Christian Schoenebeck 8522051c58 fs/9p: fix NULL pointer dereference on mkdir 
[ Upstream commit 3f61ac7c65 ]

When a 9p tree was mounted with option 'posixacl', parent directory had a
default ACL set for its subdirectories, e.g.:

  setfacl -m default:group:simpsons:rwx parentdir

then creating a subdirectory crashed 9p client, as v9fs_fid_add() call in
function v9fs_vfs_mkdir_dotl() sets the passed 'fid' pointer to NULL
(since dafbe68973) even though the subsequent v9fs_set_create_acl() call
expects a valid non-NULL 'fid' pointer:

  [   37.273191] BUG: kernel NULL pointer dereference, address: 0000000000000000
  ...
  [   37.322338] Call Trace:
  [   37.323043]  <TASK>
  [   37.323621] ? __die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434)
  [   37.324448] ? page_fault_oops (arch/x86/mm/fault.c:714)
  [   37.325532] ? search_module_extables (kernel/module/main.c:3733)
  [   37.326742] ? p9_client_walk (net/9p/client.c:1165) 9pnet
  [   37.328006] ? search_bpf_extables (kernel/bpf/core.c:804)
  [   37.329142] ? exc_page_fault (./arch/x86/include/asm/paravirt.h:686 arch/x86/mm/fault.c:1488 arch/x86/mm/fault.c:1538)
  [   37.330196] ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:574)
  [   37.331330] ? p9_client_walk (net/9p/client.c:1165) 9pnet
  [   37.332562] ? v9fs_fid_xattr_get (fs/9p/xattr.c:30) 9p
  [   37.333824] v9fs_fid_xattr_set (fs/9p/fid.h:23 fs/9p/xattr.c:121) 9p
  [   37.335077] v9fs_set_acl (fs/9p/acl.c:276) 9p
  [   37.336112] v9fs_set_create_acl (fs/9p/acl.c:307) 9p
  [   37.337326] v9fs_vfs_mkdir_dotl (fs/9p/vfs_inode_dotl.c:411) 9p
  [   37.338590] vfs_mkdir (fs/namei.c:4313)
  [   37.339535] do_mkdirat (fs/namei.c:4336)
  [   37.340465] __x64_sys_mkdir (fs/namei.c:4354)
  [   37.341455] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
  [   37.342447] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

Fix this by simply swapping the sequence of these two calls in
v9fs_vfs_mkdir_dotl(), i.e. calling v9fs_set_create_acl() before
v9fs_fid_add().

Fixes: dafbe68973 ("9p fid refcount: cleanup p9_fid_put calls")
Reported-by: syzbot+5b667f9a1fee4ba3775a@syzkaller.appspotmail.com
Signed-off-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Message-ID: <E1tsiI6-002iMG-Kh@kylie.crudebyte.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-04-10 14:39:32 +02:00
..
acl.c fs: port inode_owner_or_capable() to mnt_idmap 2023-01-19 09:24:29 +01:00
acl.h fs: port ->set_acl() to pass mnt_idmap 2023-01-19 09:24:27 +01:00
cache.c mm, netfs, fscache: stop read optimisation when folio removed from pagecache 2023-08-18 10:12:13 -07:00
cache.h fs/9p: Rework cache modes and add new options to Documentation 2023-04-09 21:41:21 +00:00
fid.c 9p: v9fs_fid_find: also lookup by inode if not found dentry 2024-09-23 05:51:27 +09:00
fid.h fs/9p: fix the cache always being enabled on files with qid flags 2024-03-28 15:10:29 +00:00
Kconfig 9p: Remove INET dependency 2023-05-04 21:46:57 +01:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
v9fs.c mm, slab: remove last vestiges of SLAB_MEM_SPREAD 2024-03-12 20:32:19 -07:00
v9fs.h Revert "fs/9p: simplify iget to remove unnecessary paths" 2024-10-25 06:26:09 +09:00
v9fs_vfs.h Revert "fs/9p: simplify iget to remove unnecessary paths" 2024-10-25 06:26:09 +09:00
vfs_addr.c netfs: Speed up buffered reading 2024-09-12 12:20:41 +02:00
vfs_dentry.c 9p: add missing locking around taking dentry fid list 2024-05-23 20:29:09 +09:00
vfs_dir.c fs/9p: rework qid2ino logic 2024-01-26 16:46:56 +00:00
vfs_file.c 9p: explicitly deny setlease attempts 2024-03-28 19:52:55 +00:00
vfs_inode.c Revert patches causing inode collision problems 2024-10-25 15:25:02 -07:00
vfs_inode_dotl.c fs/9p: fix NULL pointer dereference on mkdir 2025-04-10 14:39:32 +02:00
vfs_super.c Revert "fs/9p: simplify iget to remove unnecessary paths" 2024-10-25 06:26:09 +09:00
xattr.c Bunch of small fixes: 2023-11-04 09:20:04 -10:00
xattr.h 9p: move xattr-related structs to .rodata 2023-10-09 16:24:16 +02:00