kernel/git/stable/linux-stable.git/fs/binfmt_misc.c, branch linux-4.19.y

binfmt_misc: cleanup on filesystem umount

2024-09-04T11:13:01+00:00

[ Upstream commit 1c5976ef0f7ad76319df748ccb99a4c7ba2ba464 ] Currently, registering a new binary type pins the binfmt_misc filesystem. Specifically, this means that as long as there is at least one binary type registered the binfmt_misc filesystem survives all umounts, i.e. the superblock is not destroyed. Meaning that a umount followed by another mount will end up with the same superblock and the same binary type handlers. This is a behavior we tend to discourage for any new filesystems (apart from a few special filesystems such as e.g. configfs or debugfs). A umount operation without the filesystem being pinned - by e.g. someone holding a file descriptor to an open file - should usually result in the destruction of the superblock and all associated resources. This makes introspection easier and leads to clearly defined, simple and clean semantics. An administrator can rely on the fact that a umount will guarantee a clean slate making it possible to reinitialize a filesystem. Right now all binary types would need to be explicitly deleted before that can happen. This allows us to remove the heavy-handed calls to simple_pin_fs() and simple_release_fs() when creating and deleting binary types. This in turn allows us to replace the current brittle pinning mechanism abusing dget() which has caused a range of bugs judging from prior fixes in [2] and [3]. The additional dget() in load_misc_binary() pins the dentry but only does so for the sake to prevent ->evict_inode() from freeing the node when a user removes the binary type and kill_node() is run. Which would mean ->interpreter and ->interp_file would be freed causing a UAF. This isn't really nicely documented nor is it very clean because it relies on simple_pin_fs() pinning the filesystem as long as at least one binary type exists. Otherwise it would cause load_misc_binary() to hold on to a dentry belonging to a superblock that has been shutdown. Replace that implicit pinning with a clean and simple per-node refcount and get rid of the ugly dget() pinning. A similar mechanism exists for e.g. binderfs (cf. [4]). All the cleanup work can now be done in ->evict_inode(). In a follow-up patch we will make it possible to use binfmt_misc in sandboxes. We will use the cleaner semantics where a umount for the filesystem will cause the superblock and all resources to be deallocated. In preparation for this apply the same semantics to the initial binfmt_misc mount. Note, that this is a user-visible change and as such a uapi change but one that we can reasonably risk. We've discussed this in earlier versions of this patchset (cf. [1]). The main user and provider of binfmt_misc is systemd. Systemd provides binfmt_misc via autofs since it is configurable as a kernel module and is used by a few exotic packages and users. As such a binfmt_misc mount is triggered when /proc/sys/fs/binfmt_misc is accessed and is only provided on demand. Other autofs on demand filesystems include EFI ESP which systemd umounts if the mountpoint stays idle for a certain amount of time. This doesn't apply to the binfmt_misc autofs mount which isn't touched once it is mounted meaning this change can't accidently wipe binary type handlers without someone having explicitly unmounted binfmt_misc. After speaking to systemd folks they don't expect this change to affect them. In line with our general policy, if we see a regression for systemd or other users with this change we will switch back to the old behavior for the initial binfmt_misc mount and have binary types pin the filesystem again. But while we touch this code let's take the chance and let's improve on the status quo. [1]: https://lore.kernel.org/r/20191216091220.465626-2-laurent@vivier.eu [2]: commit 43a4f2619038 ("exec: binfmt_misc: fix race between load_misc_binary() and kill_node()" [3]: commit 83f918274e4b ("exec: binfmt_misc: shift filp_close(interp_file) from kill_node() to bm_evict_inode()") [4]: commit f0fe2c0f050d ("binder: prevent UAF for binderfs devices II") Link: https://lore.kernel.org/r/20211028103114.2849140-1-brauner@kernel.org (v1) Cc: Sargun Dhillon Cc: Serge Hallyn Cc: Jann Horn Cc: Henning Schild Cc: Andrei Vagin Cc: Al Viro Cc: Laurent Vivier Cc: linux-fsdevel@vger.kernel.org Acked-by: Serge Hallyn Signed-off-by: Christian Brauner Signed-off-by: Christian Brauner Signed-off-by: Kees Cook Signed-off-by: Sasha Levin

binfmt_misc: fix shift-out-of-bounds in check_special_flags

2023-01-18T10:30:33+00:00

[ Upstream commit 6a46bf558803dd2b959ca7435a5c143efe837217 ] UBSAN reported a shift-out-of-bounds warning: left shift of 1 by 31 places cannot be represented in type 'int' Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x8d/0xcf lib/dump_stack.c:106 ubsan_epilogue+0xa/0x44 lib/ubsan.c:151 __ubsan_handle_shift_out_of_bounds+0x1e7/0x208 lib/ubsan.c:322 check_special_flags fs/binfmt_misc.c:241 [inline] create_entry fs/binfmt_misc.c:456 [inline] bm_register_write+0x9d3/0xa20 fs/binfmt_misc.c:654 vfs_write+0x11e/0x580 fs/read_write.c:582 ksys_write+0xcf/0x120 fs/read_write.c:637 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x34/0x80 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x4194e1 Since the type of Node's flags is unsigned long, we should define these macros with same type too. Signed-off-by: Liu Shixin Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20221102025123.1117184-1-liushixin2@huawei.com Signed-off-by: Sasha Levin

binfmt_misc: fix possible deadlock in bm_register_write

2021-03-17T15:43:51+00:00

commit e7850f4d844e0acfac7e570af611d89deade3146 upstream. There is a deadlock in bm_register_write: First, in the begining of the function, a lock is taken on the binfmt_misc root inode with inode_lock(d_inode(root)). Then, if the user used the MISC_FMT_OPEN_FILE flag, the function will call open_exec on the user-provided interpreter. open_exec will call a path lookup, and if the path lookup process includes the root of binfmt_misc, it will try to take a shared lock on its inode again, but it is already locked, and the code will get stuck in a deadlock To reproduce the bug: $ echo ":iiiii:E::ii::/proc/sys/fs/binfmt_misc/bla:F" > /proc/sys/fs/binfmt_misc/register backtrace of where the lock occurs (#5): 0 schedule () at ./arch/x86/include/asm/current.h:15 1 0xffffffff81b51237 in rwsem_down_read_slowpath (sem=0xffff888003b202e0, count=, state=state@entry=2) at kernel/locking/rwsem.c:992 2 0xffffffff81b5150a in __down_read_common (state=2, sem=) at kernel/locking/rwsem.c:1213 3 __down_read (sem=) at kernel/locking/rwsem.c:1222 4 down_read (sem=) at kernel/locking/rwsem.c:1355 5 0xffffffff811ee22a in inode_lock_shared (inode=) at ./include/linux/fs.h:783 6 open_last_lookups (op=0xffffc9000022fe34, file=0xffff888004098600, nd=0xffffc9000022fd10) at fs/namei.c:3177 7 path_openat (nd=nd@entry=0xffffc9000022fd10, op=op@entry=0xffffc9000022fe34, flags=flags@entry=65) at fs/namei.c:3366 8 0xffffffff811efe1c in do_filp_open (dfd=, pathname=pathname@entry=0xffff8880031b9000, op=op@entry=0xffffc9000022fe34) at fs/namei.c:3396 9 0xffffffff811e493f in do_open_execat (fd=fd@entry=-100, name=name@entry=0xffff8880031b9000, flags=, flags@entry=0) at fs/exec.c:913 10 0xffffffff811e4a92 in open_exec (name=) at fs/exec.c:948 11 0xffffffff8124aa84 in bm_register_write (file=, buffer=, count=19, ppos=) at fs/binfmt_misc.c:682 12 0xffffffff811decd2 in vfs_write (file=file@entry=0xffff888004098500, buf=buf@entry=0xa758d0 ":iiiii:E::ii::i:CF ", count=count@entry=19, pos=pos@entry=0xffffc9000022ff10) at fs/read_write.c:603 13 0xffffffff811defda in ksys_write (fd=, buf=0xa758d0 ":iiiii:E::ii::i:CF ", count=19) at fs/read_write.c:658 14 0xffffffff81b49813 in do_syscall_64 (nr=, regs=0xffffc9000022ff58) at arch/x86/entry/common.c:46 15 0xffffffff81c0007c in entry_SYSCALL_64 () at arch/x86/entry/entry_64.S:120 To solve the issue, the open_exec call is moved to before the write lock is taken by bm_register_write Link: https://lkml.kernel.org/r/20210228224414.95962-1-liorribak@gmail.com Fixes: 948b701a607f1 ("binfmt_misc: add persistent opened binary handler for containers") Signed-off-by: Lior Ribak Acked-by: Helge Deller Cc: Al Viro Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

turn filp_clone_open() into inline wrapper for dentry_open()

2018-07-11T03:29:03+00:00

it's exactly the same thing as dentry_open(&file->f_path, file->f_flags, file->f_cred) ... and rename it to file_clone_open(), while we are at it. 'filp' naming convention is bogus; sure, it's "file pointer", but we generally don't do that kind of Hungarian notation. Some of the instances have too many callers to touch, but this one has only two, so let's sanitize it while we can... Acked-by: Linus Torvalds Signed-off-by: Al Viro

docs: Fix more broken references

2018-06-15T21:11:26+00:00

As we move stuff around, some doc references are broken. Fix some of them via this script: ./scripts/documentation-file-ref-check --fix Manually checked that produced results are valid. Acked-by: Matthias Brugger Acked-by: Takashi Iwai Acked-by: Jeff Kirsher Acked-by: Guenter Roeck Acked-by: Miguel Ojeda Signed-off-by: Mauro Carvalho Chehab Acked-by: Jonathan Corbet

fs/binfmt_misc.c: do not allow offset overflow

2018-06-08T00:34:39+00:00

WHen registering a new binfmt_misc handler, it is possible to overflow the offset to get a negative value, which might crash the system, or possibly leak kernel data. Here is a crash log when 2500000000 was used as an offset: BUG: unable to handle kernel paging request at ffff989cfd6edca0 IP: load_misc_binary+0x22b/0x470 [binfmt_misc] PGD 1ef3e067 P4D 1ef3e067 PUD 0 Oops: 0000 [#1] SMP NOPTI Modules linked in: binfmt_misc kvm_intel ppdev kvm irqbypass joydev input_leds serio_raw mac_hid parport_pc qemu_fw_cfg parpy CPU: 0 PID: 2499 Comm: bash Not tainted 4.15.0-22-generic #24-Ubuntu Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-1 04/01/2014 RIP: 0010:load_misc_binary+0x22b/0x470 [binfmt_misc] Call Trace: search_binary_handler+0x97/0x1d0 do_execveat_common.isra.34+0x667/0x810 SyS_execve+0x31/0x40 do_syscall_64+0x73/0x130 entry_SYSCALL_64_after_hwframe+0x3d/0xa2 Use kstrtoint instead of simple_strtoul. It will work as the code already set the delimiter byte to '\0' and we only do it when the field is not empty. Tested with offsets -1, 2500000000, UINT_MAX and INT_MAX. Also tested with examples documented at Documentation/admin-guide/binfmt-misc.rst and other registrations from packages on Ubuntu. Link: http://lkml.kernel.org/r/20180529135648.14254-1-cascardo@canonical.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Thadeu Lima de Souza Cascardo Reviewed-by: Andrew Morton Cc: Alexander Viro Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

fs: add ksys_close() wrapper; remove in-kernel calls to sys_close()

2018-04-02T18:16:00+00:00

Using the ksys_close() wrapper allows us to get rid of in-kernel calls to the sys_close() syscall. The ksys_ prefix denotes that this function is meant as a drop-in replacement for the syscall. In particular, it uses the same calling convention as sys_close(), with one subtle difference: The few places which checked the return value did not care about the return value re-writing in sys_close(), so simply use a wrapper around __close_fd(). This patch is part of a series which removes in-kernel calls to syscalls. On this basis, the syscall entry path can be streamlined. For details, see http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net Cc: Al Viro Cc: Andrew Morton Signed-off-by: Dominik Brodowski

fs/binfmt_misc.c: node could be NULL when evicting inode

2017-10-13T23:18:33+00:00

inode->i_private is assigned by a Node pointer only after registering a new binary format, so it could be NULL if inode was created by bm_fill_super() (or iput() was called by the error path in bm_register_write()), and this could result in NULL pointer dereference when evicting such an inode. e.g. mount binfmt_misc filesystem then umount it immediately: mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc umount /proc/sys/fs/binfmt_misc will result in BUG: unable to handle kernel NULL pointer dereference at 0000000000000013 IP: bm_evict_inode+0x16/0x40 [binfmt_misc] ... Call Trace: evict+0xd3/0x1a0 iput+0x17d/0x1d0 dentry_unlink_inode+0xb9/0xf0 __dentry_kill+0xc7/0x170 shrink_dentry_list+0x122/0x280 shrink_dcache_parent+0x39/0x90 do_one_tree+0x12/0x40 shrink_dcache_for_umount+0x2d/0x90 generic_shutdown_super+0x1f/0x120 kill_litter_super+0x29/0x40 deactivate_locked_super+0x43/0x70 deactivate_super+0x45/0x60 cleanup_mnt+0x3f/0x70 __cleanup_mnt+0x12/0x20 task_work_run+0x86/0xa0 exit_to_usermode_loop+0x6d/0x99 syscall_return_slowpath+0xba/0xf0 entry_SYSCALL_64_fastpath+0xa3/0xa Fix it by making sure Node (e) is not NULL. Link: http://lkml.kernel.org/r/20171010100642.31786-1-eguan@redhat.com Fixes: 83f918274e4b ("exec: binfmt_misc: shift filp_close(interp_file) from kill_node() to bm_evict_inode()") Signed-off-by: Eryu Guan Acked-by: Oleg Nesterov Cc: Alexander Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

exec: binfmt_misc: kill the onstack iname[BINPRM_BUF_SIZE] array

2017-10-04T00:54:25+00:00

After the previous change "fmt" can't go away, we can kill iname/iname_addr and use fmt->interpreter. Link: http://lkml.kernel.org/r/20170922143653.GA17232@redhat.com Signed-off-by: Oleg Nesterov Acked-by: Kees Cook Cc: Al Viro Cc: Ben Woodard Cc: James Bottomley Cc: Jim Foraker Cc: Cc: Travis Gummels Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

exec: binfmt_misc: fix race between load_misc_binary() and kill_node()

2017-10-04T00:54:25+00:00

load_misc_binary() makes a local copy of fmt->interpreter under entries_lock to avoid the race with kill_node() but this is not enough; the whole Node can be freed after we drop entries_lock, not only the ->interpreter string. Add dget/dput(fmt->dentry) to ensure bm_evict_inode() can't destroy/free this Node. Link: http://lkml.kernel.org/r/20170922143650.GA17227@redhat.com Signed-off-by: Oleg Nesterov Acked-by: Kees Cook Cc: Al Viro Cc: Ben Woodard Cc: James Bottomley Cc: Jim Foraker Cc: Travis Gummels Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds