user/sven/linux.git/fs/exec.c, branch v5.4.300

parisc: Fix stack start for ADDR_NO_RANDOMIZE personality

2024-11-08T15:20:40Z

commit f31b256994acec6929306dfa86ac29716e7503d6 upstream. Fix the stack start address calculation for the parisc architecture in setup_arg_pages() when address randomization is disabled. When the ADDR_NO_RANDOMIZE process personality is disabled there is no need to add additional space for the stack. Note that this patch touches code inside an #ifdef CONFIG_STACK_GROWSUP hunk, which is why only the parisc architecture is affected since it's the only Linux architecture where the stack grows upwards. Without this patch you will find the stack in the middle of some mapped libaries and suddenly limited to 6MB instead of 8MB: root@parisc:~# setarch -R /bin/bash -c "cat /proc/self/maps" 00010000-00019000 r-xp 00000000 08:05 1182034 /usr/bin/cat 00019000-0001a000 rwxp 00009000 08:05 1182034 /usr/bin/cat 0001a000-0003b000 rwxp 00000000 00:00 0 [heap] f90c4000-f9283000 r-xp 00000000 08:05 1573004 /usr/lib/hppa-linux-gnu/libc.so.6 f9283000-f9285000 r--p 001bf000 08:05 1573004 /usr/lib/hppa-linux-gnu/libc.so.6 f9285000-f928a000 rwxp 001c1000 08:05 1573004 /usr/lib/hppa-linux-gnu/libc.so.6 f928a000-f9294000 rwxp 00000000 00:00 0 f9301000-f9323000 rwxp 00000000 00:00 0 [stack] f98b4000-f98e4000 r-xp 00000000 08:05 1572869 /usr/lib/hppa-linux-gnu/ld.so.1 f98e4000-f98e5000 r--p 00030000 08:05 1572869 /usr/lib/hppa-linux-gnu/ld.so.1 f98e5000-f98e9000 rwxp 00031000 08:05 1572869 /usr/lib/hppa-linux-gnu/ld.so.1 f9ad8000-f9b00000 rw-p 00000000 00:00 0 f9b00000-f9b01000 r-xp 00000000 00:00 0 [vdso] With the patch the stack gets correctly mapped at the end of the process memory map: root@panama:~# setarch -R /bin/bash -c "cat /proc/self/maps" 00010000-00019000 r-xp 00000000 08:13 16385582 /usr/bin/cat 00019000-0001a000 rwxp 00009000 08:13 16385582 /usr/bin/cat 0001a000-0003b000 rwxp 00000000 00:00 0 [heap] fef29000-ff0eb000 r-xp 00000000 08:13 16122400 /usr/lib/hppa-linux-gnu/libc.so.6 ff0eb000-ff0ed000 r--p 001c2000 08:13 16122400 /usr/lib/hppa-linux-gnu/libc.so.6 ff0ed000-ff0f2000 rwxp 001c4000 08:13 16122400 /usr/lib/hppa-linux-gnu/libc.so.6 ff0f2000-ff0fc000 rwxp 00000000 00:00 0 ff4b4000-ff4e4000 r-xp 00000000 08:13 16121913 /usr/lib/hppa-linux-gnu/ld.so.1 ff4e4000-ff4e6000 r--p 00030000 08:13 16121913 /usr/lib/hppa-linux-gnu/ld.so.1 ff4e6000-ff4ea000 rwxp 00032000 08:13 16121913 /usr/lib/hppa-linux-gnu/ld.so.1 ff6d7000-ff6ff000 rw-p 00000000 00:00 0 ff6ff000-ff700000 r-xp 00000000 00:00 0 [vdso] ff700000-ff722000 rwxp 00000000 00:00 0 [stack] Reported-by: Camm Maguire Signed-off-by: Helge Deller Fixes: d045c77c1a69 ("parisc,metag: Fix crashes due to stack randomization on stack-grows-upwards architectures") Fixes: 17d9822d4b4c ("parisc: Consider stack randomization for mmap base only when necessary") Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Greg Kroah-Hartman

exec: Fix ToCToU between perm check and set-uid/gid usage

2024-08-19T03:33:54Z

commit f50733b45d865f91db90919f8311e2127ce5a0cb upstream. When opening a file for exec via do_filp_open(), permission checking is done against the file's metadata at that moment, and on success, a file pointer is passed back. Much later in the execve() code path, the file metadata (specifically mode, uid, and gid) is used to determine if/how to set the uid and gid. However, those values may have changed since the permissions check, meaning the execution may gain unintended privileges. For example, if a file could change permissions from executable and not set-id: ---------x 1 root root 16048 Aug 7 13:16 target to set-id and non-executable: ---S------ 1 root root 16048 Aug 7 13:16 target it is possible to gain root privileges when execution should have been disallowed. While this race condition is rare in real-world scenarios, it has been observed (and proven exploitable) when package managers are updating the setuid bits of installed programs. Such files start with being world-executable but then are adjusted to be group-exec with a set-uid bit. For example, "chmod o-x,u+s target" makes "target" executable only by uid "root" and gid "cdrom", while also becoming setuid-root: -rwxr-xr-x 1 root cdrom 16048 Aug 7 13:16 target becomes: -rwsr-xr-- 1 root cdrom 16048 Aug 7 13:16 target But racing the chmod means users without group "cdrom" membership can get the permission to execute "target" just before the chmod, and when the chmod finishes, the exec reaches brpm_fill_uid(), and performs the setuid to root, violating the expressed authorization of "only cdrom group members can setuid to root". Re-check that we still have execute permissions in case the metadata has changed. It would be better to keep a copy from the perm-check time, but until we can do that refactoring, the least-bad option is to do a full inode_permission() call (under inode lock). It is understood that this is safe against dead-locks, but hardly optimal. Reported-by: Marco Vanotti Tested-by: Marco Vanotti Suggested-by: Linus Torvalds Cc: stable@vger.kernel.org Cc: Eric Biederman Cc: Alexander Viro Cc: Christian Brauner Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman

exec: Fix NOMMU linux_binprm::exec in transfer_args_to_stack()

2024-04-13T10:51:31Z

commit 2aea94ac14d1e0a8ae9e34febebe208213ba72f7 upstream. In NOMMU kernel the value of linux_binprm::p is the offset inside the temporary program arguments array maintained in separate pages in the linux_binprm::page. linux_binprm::exec being a copy of linux_binprm::p thus must be adjusted when that array is copied to the user stack. Without that adjustment the value passed by the NOMMU kernel to the ELF program in the AT_EXECFN entry of the aux array doesn't make any sense and it may break programs that try to access memory pointed to by that entry. Adjust linux_binprm::exec before the successful return from the transfer_args_to_stack(). Cc: Fixes: b6a2fea39318 ("mm: variable length argument support") Fixes: 5edc2a5123a7 ("binfmt_elf_fdpic: wire up AT_EXECFD, AT_EXECFN, AT_SECURE") Signed-off-by: Max Filippov Link: https://lore.kernel.org/r/20240320182607.1472887-1-jcmvbkbc@gmail.com Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman

exec: Force single empty string when argv is empty

2022-06-06T06:33:50Z

commit dcd46d897adb70d63e025f175a00a89797d31a43 upstream. Quoting[1] Ariadne Conill: "In several other operating systems, it is a hard requirement that the second argument to execve(2) be the name of a program, thus prohibiting a scenario where argc < 1. POSIX 2017 also recommends this behaviour, but it is not an explicit requirement[2]: The argument arg0 should point to a filename string that is associated with the process being started by one of the exec functions. ... Interestingly, Michael Kerrisk opened an issue about this in 2008[3], but there was no consensus to support fixing this issue then. Hopefully now that CVE-2021-4034 shows practical exploitative use[4] of this bug in a shellcode, we can reconsider. This issue is being tracked in the KSPP issue tracker[5]." While the initial code searches[6][7] turned up what appeared to be mostly corner case tests, trying to that just reject argv == NULL (or an immediately terminated pointer list) quickly started tripping[8] existing userspace programs. The next best approach is forcing a single empty string into argv and adjusting argc to match. The number of programs depending on argc == 0 seems a smaller set than those calling execve with a NULL argv. Account for the additional stack space in bprm_stack_limits(). Inject an empty string when argc == 0 (and set argc = 1). Warn about the case so userspace has some notice about the change: process './argc0' launched './argc0' with NULL argv: empty string added Additionally WARN() and reject NULL argv usage for kernel threads. [1] https://lore.kernel.org/lkml/20220127000724.15106-1-ariadne@dereferenced.org/ [2] https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html [3] https://bugzilla.kernel.org/show_bug.cgi?id=8408 [4] https://www.qualys.com/2022/01/25/cve-2021-4034/pwnkit.txt [5] https://github.com/KSPP/linux/issues/176 [6] https://codesearch.debian.net/search?q=execve%5C+*%5C%28%5B%5E%2C%5D%2B%2C+*NULL&literal=0 [7] https://codesearch.debian.net/search?q=execlp%3F%5Cs*%5C%28%5B%5E%2C%5D%2B%2C%5Cs*NULL&literal=0 [8] https://lore.kernel.org/lkml/20220131144352.GE16385@xsang-OptiPlex-9020/ Reported-by: Ariadne Conill Reported-by: Michael Kerrisk Cc: Matthew Wilcox Cc: Christian Brauner Cc: Rich Felker Cc: Eric Biederman Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Kees Cook Acked-by: Christian Brauner Acked-by: Ariadne Conill Acked-by: Andy Lutomirski Link: https://lore.kernel.org/r/20220201000947.2453721-1-keescook@chromium.org [vegard: fixed conflicts due to missing 886d7de631da71e30909980fdbf318f7caade262^- and 3950e975431bc914f7e81b8f2a2dbdf2064acb0f^-] Signed-off-by: Vegard Nossum Signed-off-by: Greg Kroah-Hartman

vfs: check fd has read access in kernel_read_file_from_fd()

2021-10-27T07:54:27Z

commit 032146cda85566abcd1c4884d9d23e4e30a07e9a upstream. If we open a file without read access and then pass the fd to a syscall whose implementation calls kernel_read_file_from_fd(), we get a warning from __kernel_read(): if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ))) This currently affects both finit_module() and kexec_file_load(), but it could affect other syscalls in the future. Link: https://lkml.kernel.org/r/20211007220110.600005-1-willy@infradead.org Fixes: b844f0ecbc56 ("vfs: define kernel_copy_file_from_fd()") Signed-off-by: Matthew Wilcox (Oracle) Reported-by: Hao Sun Reviewed-by: Kees Cook Acked-by: Christian Brauner Cc: Al Viro Cc: Mimi Zohar Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

exec: Transform exec_update_mutex into a rw_semaphore

2021-01-09T12:44:55Z

[ Upstream commit f7cfd871ae0c5008d94b6f66834e7845caa93c15 ] Recently syzbot reported[0] that there is a deadlock amongst the users of exec_update_mutex. The problematic lock ordering found by lockdep was: perf_event_open (exec_update_mutex -> ovl_i_mutex) chown (ovl_i_mutex -> sb_writes) sendfile (sb_writes -> p->lock) by reading from a proc file and writing to overlayfs proc_pid_syscall (p->lock -> exec_update_mutex) While looking at possible solutions it occured to me that all of the users and possible users involved only wanted to state of the given process to remain the same. They are all readers. The only writer is exec. There is no reason for readers to block on each other. So fix this deadlock by transforming exec_update_mutex into a rw_semaphore named exec_update_lock that only exec takes for writing. Cc: Jann Horn Cc: Vasiliy Kulikov Cc: Al Viro Cc: Bernd Edlinger Cc: Oleg Nesterov Cc: Christopher Yeoh Cc: Cyrill Gorcunov Cc: Sargun Dhillon Cc: Christian Brauner Cc: Arnd Bergmann Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo Fixes: eea9673250db ("exec: Add exec_update_mutex to replace cred_guard_mutex") [0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.org Signed-off-by: Eric W. Biederman Signed-off-by: Sasha Levin

mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race

2020-11-05T10:43:13Z

[ Upstream commit d53c3dfb23c45f7d4f910c3a3ca84bf0a99c6143 ] Reading and modifying current->mm and current->active_mm and switching mm should be done with irqs off, to prevent races seeing an intermediate state. This is similar to commit 38cf307c1f20 ("mm: fix kthread_use_mm() vs TLB invalidate"). At exec-time when the new mm is activated, the old one should usually be single-threaded and no longer used, unless something else is holding an mm_users reference (which may be possible). Absent other mm_users, there is also a race with preemption and lazy tlb switching. Consider the kernel_execve case where the current thread is using a lazy tlb active mm: call_usermodehelper() kernel_execve() old_mm = current->mm; active_mm = current->active_mm; *** preempt *** --------------------> schedule() prev->active_mm = NULL; mmdrop(prev active_mm); ... <-------------------- schedule() current->mm = mm; current->active_mm = mm; if (!old_mm) mmdrop(active_mm); If we switch back to the kernel thread from a different mm, there is a double free of the old active_mm, and a missing free of the new one. Closing this race only requires interrupts to be disabled while ->mm and ->active_mm are being switched, but the TLB problem requires also holding interrupts off over activate_mm. Unfortunately not all archs can do that yet, e.g., arm defers the switch if irqs are disabled and expects finish_arch_post_lock_switch() to be called to complete the flush; um takes a blocking lock in activate_mm(). So as a first step, disable interrupts across the mm/active_mm updates to close the lazy tlb preempt race, and provide an arch option to extend that to activate_mm which allows architectures doing IPI based TLB shootdowns to close the second race. This is a bit ugly, but in the interest of fixing the bug and backporting before all architectures are converted this is a compromise. Signed-off-by: Nicholas Piggin Acked-by: Peter Zijlstra (Intel) Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200914045219.3736466-2-npiggin@gmail.com Signed-off-by: Sasha Levin

exec: Add exec_update_mutex to replace cred_guard_mutex

2020-10-01T11:17:47Z

[ Upstream commit eea9673250db4e854e9998ef9da6d4584857f0ea ] The cred_guard_mutex is problematic as it is held over possibly indefinite waits for userspace. The possible indefinite waits for userspace that I have identified are: The cred_guard_mutex is held in PTRACE_EVENT_EXIT waiting for the tracer. The cred_guard_mutex is held over "put_user(0, tsk->clear_child_tid)" in exit_mm(). The cred_guard_mutex is held over "get_user(futex_offset, ...") in exit_robust_list. The cred_guard_mutex held over copy_strings. The functions get_user and put_user can trigger a page fault which can potentially wait indefinitely in the case of userfaultfd or if userspace implements part of the page fault path. In any of those cases the userspace process that the kernel is waiting for might make a different system call that winds up taking the cred_guard_mutex and result in deadlock. Holding a mutex over any of those possibly indefinite waits for userspace does not appear necessary. Add exec_update_mutex that will just cover updating the process during exec where the permissions and the objects pointed to by the task struct may be out of sync. The plan is to switch the users of cred_guard_mutex to exec_update_mutex one by one. This lets us move forward while still being careful and not introducing any regressions. Link: https://lore.kernel.org/lkml/20160921152946.GA24210@dhcp22.suse.cz/ Link: https://lore.kernel.org/lkml/AM6PR03MB5170B06F3A2B75EFB98D071AE4E60@AM6PR03MB5170.eurprd03.prod.outlook.com/ Link: https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@redhat.com/ Link: https://lore.kernel.org/lkml/20160923095031.GA14923@redhat.com/ Link: https://lore.kernel.org/lkml/20170213141452.GA30203@redhat.com/ Ref: 45c1a159b85b ("Add PTRACE_O_TRACEVFORKDONE and PTRACE_O_TRACEEXIT facilities.") Ref: 456f17cd1a28 ("[PATCH] user-vm-unlock-2.5.31-A2") Reviewed-by: Kirill Tkhai Signed-off-by: "Eric W. Biederman" Signed-off-by: Bernd Edlinger Signed-off-by: Eric W. Biederman Signed-off-by: Sasha Levin

exec: Move would_dump into flush_old_exec

2020-05-20T06:20:34Z

commit f87d1c9559164294040e58f5e3b74a162bf7c6e8 upstream. I goofed when I added mm->user_ns support to would_dump. I missed the fact that in the case of binfmt_loader, binfmt_em86, binfmt_misc, and binfmt_script bprm->file is reassigned. Which made the move of would_dump from setup_new_exec to __do_execve_file before exec_binprm incorrect as it can result in would_dump running on the script instead of the interpreter of the script. The net result is that the code stopped making unreadable interpreters undumpable. Which allows them to be ptraced and written to disk without special permissions. Oops. The move was necessary because the call in set_new_exec was after bprm->mm was no longer valid. To correct this mistake move the misplaced would_dump from __do_execve_file into flos_old_exec, before exec_mmap is called. I tested and confirmed that without this fix I can attach with gdb to a script with an unreadable interpreter, and with this fix I can not. Cc: stable@vger.kernel.org Fixes: f84df2a6f268 ("exec: Ensure mm->user_ns contains the execed files") Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman

signal: Extend exec_id to 64bits

2020-04-17T08:50:12Z

commit d1e7fd6462ca9fc76650fbe6ca800e35b24267da upstream. Replace the 32bit exec_id with a 64bit exec_id to make it impossible to wrap the exec_id counter. With care an attacker can cause exec_id wrap and send arbitrary signals to a newly exec'd parent. This bypasses the signal sending checks if the parent changes their credentials during exec. The severity of this problem can been seen that in my limited testing of a 32bit exec_id it can take as little as 19s to exec 65536 times. Which means that it can take as little as 14 days to wrap a 32bit exec_id. Adam Zabrocki has succeeded wrapping the self_exe_id in 7 days. Even my slower timing is in the uptime of a typical server. Which means self_exec_id is simply a speed bump today, and if exec gets noticably faster self_exec_id won't even be a speed bump. Extending self_exec_id to 64bits introduces a problem on 32bit architectures where reading self_exec_id is no longer atomic and can take two read instructions. Which means that is is possible to hit a window where the read value of exec_id does not match the written value. So with very lucky timing after this change this still remains expoiltable. I have updated the update of exec_id on exec to use WRITE_ONCE and the read of exec_id in do_notify_parent to use READ_ONCE to make it clear that there is no locking between these two locations. Link: https://lore.kernel.org/kernel-hardening/20200324215049.GA3710@pi3.com.pl Fixes: 2.3.23pre2 Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman