kernel/linux.git/fs/binfmt_misc.c, branch v6.6.131

binfmt_misc: restore write access before closing files opened by open_exec()

2026-03-25T10:06:01+00:00

[ Upstream commit 90f601b497d76f40fa66795c3ecf625b6aced9fd ] bm_register_write() opens an executable file using open_exec(), which internally calls do_open_execat() and denies write access on the file to avoid modification while it is being executed. However, when an error occurs, bm_register_write() closes the file using filp_close() directly. This does not restore the write permission, which may cause subsequent write operations on the same file to fail. Fix this by calling exe_file_allow_write_access() before filp_close() to restore the write permission properly. Fixes: e7850f4d844e ("binfmt_misc: fix possible deadlock in bm_register_write") Signed-off-by: Zilin Guan Link: https://patch.msgid.link/20251105022923.1813587-1-zilin@seu.edu.cn Signed-off-by: Christian Brauner [ Use allow_write_access() instead of exe_file_allow_write_access() according to commit 0357ef03c94ef ("fs: don't block write during exec on pre-content watched files"). ] Signed-off-by: Robert Garcia Signed-off-by: Greg Kroah-Hartman

binfmt_misc: cleanup on filesystem umount

2024-08-29T15:33:27+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

fs: convert to ctime accessor functions

2023-07-13T08:28:04+00:00

In later patches, we're going to change how the inode's ctime field is used. Switch to using accessor functions instead of raw accesses of inode->i_ctime. Reviewed-by: Jan Kara Signed-off-by: Jeff Layton Message-Id: <20230705190309.579783-23-jlayton@kernel.org> Signed-off-by: Christian Brauner

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

2022-12-02T21:57:04+00:00

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

Fix regression due to "fs: move binfmt_misc sysctl to its own file"

2022-02-09T17:50:02+00:00

Commit 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file") did not go unnoticed, binfmt-support stopped to work on my Debian system since v5.17-rc2 (did not check with -rc1). The existance of the /proc/sys/fs/binfmt_misc is a precondition for attempting to mount the binfmt_misc fs, which in turn triggers the autoload of the binfmt_misc module. Without it, no module is loaded and no binfmt is available at boot. Building as built-in or manually loading the module and mounting the fs works fine, it's therefore only a matter of interaction with user-space. I could try to improve the Debian systemd configuration but I can't say anything about the other distributions. This patch restores a working system right after boot. Fixes: 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file") Signed-off-by: Domenico Andreoli Cc: Andrew Morton Cc: Luis Chamberlain Reviewed-by: Tong Zhang Signed-off-by: Linus Torvalds

binfmt_misc: fix crash when load/unload module

2022-01-30T07:56:58+00:00

We should unregister the table upon module unload otherwise something horrible will happen when we load binfmt_misc module again. Also note that we should keep value returned by register_sysctl_mount_point() and release it later, otherwise it will leak. Also, per Christian's comment, to fully restore the old behavior that won't break userspace the check(binfmt_misc_header) should be eliminated. To reproduce: modprobe binfmt_misc modprobe -r binfmt_misc modprobe binfmt_misc modprobe -r binfmt_misc modprobe binfmt_misc resulting in modprobe: can't load module binfmt_misc (kernel/fs/binfmt_misc.ko): Cannot allocate memory and an unhappy kernel: binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point BUG: unable to handle page fault for address: fffffbfff8004802 Call Trace: init_misc_binfmt+0x2d/0x1000 [binfmt_misc] Link: https://lkml.kernel.org/r/20220124181812.1869535-2-ztong0001@gmail.com Fixes: 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file") Signed-off-by: Tong Zhang Co-developed-by: Christian Brauner Acked-by: Luis Chamberlain Cc: Eric Biederman Cc: Kees Cook Cc: Iurii Zaikin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

fs: move binfmt_misc sysctl to its own file

2022-01-22T06:33:35+00:00

kernel/sysctl.c is a kitchen sink where everyone leaves their dirty dishes, this makes it very difficult to maintain. To help with this maintenance let's start by moving sysctls to places where they actually belong. The proc sysctl maintainers do not want to know what sysctl knobs you wish to add for your own piece of code, we just care about the core logic. This moves the binfmt_misc sysctl to its own file to help remove clutter from kernel/sysctl.c. Link: https://lkml.kernel.org/r/20211124231435.1445213-5-mcgrof@kernel.org Signed-off-by: Luis Chamberlain Cc: Al Viro Cc: Amir Goldstein Cc: Andy Shevchenko Cc: Antti Palosaari Cc: Arnd Bergmann Cc: Benjamin Herrenschmidt Cc: Benjamin LaHaise Cc: Clemens Ladisch Cc: David Airlie Cc: Douglas Gilbert Cc: Eric Biederman Cc: Greg Kroah-Hartman Cc: Iurii Zaikin Cc: James E.J. Bottomley Cc: Jani Nikula Cc: Jani Nikula Cc: Jan Kara Cc: Joel Becker Cc: John Ogness Cc: Joonas Lahtinen Cc: Joseph Qi Cc: Julia Lawall Cc: Kees Cook Cc: Lukas Middendorf Cc: Mark Fasheh Cc: Martin K. Petersen Cc: Paul Turner Cc: Peter Zijlstra Cc: Petr Mladek Cc: Phillip Potter Cc: Qing Wang Cc: "Rafael J. Wysocki" Cc: Rodrigo Vivi Cc: Sebastian Reichel Cc: Sergey Senozhatsky Cc: Stephen Kitt Cc: Steven Rostedt (VMware) Cc: Suren Baghdasaryan Cc: Tetsuo Handa Cc: "Theodore Ts'o" Cc: Xiaoming Ni Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

binfmt_misc: fix possible deadlock in bm_register_write

2021-03-13T19:27:30+00:00

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

binfmt_misc: pass binfmt_misc flags to the interpreter

2021-02-15T17:28:30+00:00

It can be useful to the interpreter to know which flags are in use. For instance, knowing if the preserve-argv[0] is in use would allow to skip the pathname argument. This patch uses an unused auxiliary vector, AT_FLAGS, to add a flag to inform interpreter if the preserve-argv[0] is enabled. Note by Helge Deller: The real-world user of this patch is qemu-user, which needs to know if it has to preserve the argv[0]. See Debian bug #970460. Signed-off-by: Laurent Vivier Reviewed-by: YunQiang Su URL: http://bugs.debian.org/970460 Signed-off-by: Helge Deller

Merge branch 'akpm' (patches from Andrew)

2020-06-05T02:18:29+00:00

Merge yet more updates from Andrew Morton: - More MM work. 100ish more to go. Mike Rapoport's "mm: remove __ARCH_HAS_5LEVEL_HACK" series should fix the current ppc issue - Various other little subsystems * emailed patches from Andrew Morton : (127 commits) lib/ubsan.c: fix gcc-10 warnings tools/testing/selftests/vm: remove duplicate headers selftests: vm: pkeys: fix multilib builds for x86 selftests: vm: pkeys: use the correct page size on powerpc selftests/vm/pkeys: override access right definitions on powerpc selftests/vm/pkeys: test correct behaviour of pkey-0 selftests/vm/pkeys: introduce a sub-page allocator selftests/vm/pkeys: detect write violation on a mapped access-denied-key page selftests/vm/pkeys: associate key on a mapped page and detect write violation selftests/vm/pkeys: associate key on a mapped page and detect access violation selftests/vm/pkeys: improve checks to determine pkey support selftests/vm/pkeys: fix assertion in test_pkey_alloc_exhaust() selftests/vm/pkeys: fix number of reserved powerpc pkeys selftests/vm/pkeys: introduce powerpc support selftests/vm/pkeys: introduce generic pkey abstractions selftests: vm: pkeys: use the correct huge page size selftests/vm/pkeys: fix alloc_random_pkey() to make it really random selftests/vm/pkeys: fix assertion in pkey_disable_set/clear() selftests/vm/pkeys: fix pkey_disable_clear() selftests: vm: pkeys: add helpers for pkey bits ...