user/sven/linux.git/kernel/ptrace.c, branch v5.9.2

ptrace: reintroduce usage of subjective credentials in ptrace_has_cap()

2020-01-18T12:51:39Z

Commit 69f594a38967 ("ptrace: do not audit capability check when outputing /proc/pid/stat") introduced the ability to opt out of audit messages for accesses to various proc files since they are not violations of policy. While doing so it somehow switched the check from ns_capable() to has_ns_capability{_noaudit}(). That means it switched from checking the subjective credentials of the task to using the objective credentials. This is wrong since. ptrace_has_cap() is currently only used in ptrace_may_access() And is used to check whether the calling task (subject) has the CAP_SYS_PTRACE capability in the provided user namespace to operate on the target task (object). According to the cred.h comments this would mean the subjective credentials of the calling task need to be used. This switches ptrace_has_cap() to use security_capable(). Because we only call ptrace_has_cap() in ptrace_may_access() and in there we already have a stable reference to the calling task's creds under rcu_read_lock() there's no need to go through another series of dereferences and rcu locking done in ns_capable{_noaudit}(). As one example where this might be particularly problematic, Jann pointed out that in combination with the upcoming IORING_OP_OPENAT feature, this bug might allow unprivileged users to bypass the capability checks while asynchronously opening files like /proc/*/mem, because the capability checks for this would be performed against kernel credentials. To illustrate on the former point about this being exploitable: When io_uring creates a new context it records the subjective credentials of the caller. Later on, when it starts to do work it creates a kernel thread and registers a callback. The callback runs with kernel creds for ktask->real_cred and ktask->cred. To prevent this from becoming a full-blown 0-day io_uring will call override_cred() and override ktask->cred with the subjective credentials of the creator of the io_uring instance. With ptrace_has_cap() currently looking at ktask->real_cred this override will be ineffective and the caller will be able to open arbitray proc files as mentioned above. Luckily, this is currently not exploitable but will turn into a 0-day once IORING_OP_OPENAT{2} land in v5.6. Fix it now! Cc: Oleg Nesterov Cc: Eric Paris Cc: stable@vger.kernel.org Reviewed-by: Kees Cook Reviewed-by: Serge Hallyn Reviewed-by: Jann Horn Fixes: 69f594a38967 ("ptrace: do not audit capability check when outputing /proc/pid/stat") Signed-off-by: Christian Brauner

ptrace: add PTRACE_GET_SYSCALL_INFO request

2019-07-17T02:23:24Z

PTRACE_GET_SYSCALL_INFO is a generic ptrace API that lets ptracer obtain details of the syscall the tracee is blocked in. There are two reasons for a special syscall-related ptrace request. Firstly, with the current ptrace API there are cases when ptracer cannot retrieve necessary information about syscalls. Some examples include: * The notorious int-0x80-from-64-bit-task issue. See [1] for details. In short, if a 64-bit task performs a syscall through int 0x80, its tracer has no reliable means to find out that the syscall was, in fact, a compat syscall, and misidentifies it. * Syscall-enter-stop and syscall-exit-stop look the same for the tracer. Common practice is to keep track of the sequence of ptrace-stops in order not to mix the two syscall-stops up. But it is not as simple as it looks; for example, strace had a (just recently fixed) long-standing bug where attaching strace to a tracee that is performing the execve system call led to the tracer identifying the following syscall-exit-stop as syscall-enter-stop, which messed up all the state tracking. * Since the introduction of commit 84d77d3f06e7 ("ptrace: Don't allow accessing an undumpable mm"), both PTRACE_PEEKDATA and process_vm_readv become unavailable when the process dumpable flag is cleared. On such architectures as ia64 this results in all syscall arguments being unavailable for the tracer. Secondly, ptracers also have to support a lot of arch-specific code for obtaining information about the tracee. For some architectures, this requires a ptrace(PTRACE_PEEKUSER, ...) invocation for every syscall argument and return value. ptrace(2) man page: long ptrace(enum __ptrace_request request, pid_t pid, void *addr, void *data); ... PTRACE_GET_SYSCALL_INFO Retrieve information about the syscall that caused the stop. The information is placed into the buffer pointed by "data" argument, which should be a pointer to a buffer of type "struct ptrace_syscall_info". The "addr" argument contains the size of the buffer pointed to by "data" argument (i.e., sizeof(struct ptrace_syscall_info)). The return value contains the number of bytes available to be written by the kernel. If the size of data to be written by the kernel exceeds the size specified by "addr" argument, the output is truncated. [ldv@altlinux.org: selftests/seccomp/seccomp_bpf: update for PTRACE_GET_SYSCALL_INFO] Link: http://lkml.kernel.org/r/20190708182904.GA12332@altlinux.org Link: http://lkml.kernel.org/r/20190510152842.GF28558@altlinux.org Signed-off-by: Elvira Khabirova Co-developed-by: Dmitry V. Levin Signed-off-by: Dmitry V. Levin Reviewed-by: Oleg Nesterov Reviewed-by: Kees Cook Reviewed-by: Andy Lutomirski Cc: Eugene Syromyatnikov Cc: Benjamin Herrenschmidt Cc: Greentime Hu Cc: Helge Deller [parisc] Cc: James E.J. Bottomley Cc: James Hogan Cc: kbuild test robot Cc: Michael Ellerman Cc: Paul Burton Cc: Paul Mackerras Cc: Ralf Baechle Cc: Richard Kuo Cc: Shuah Khan Cc: Vincent Chen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

2019-07-08T16:54:55Z

Pull arm64 updates from Catalin Marinas: - arm64 support for syscall emulation via PTRACE_SYSEMU{,_SINGLESTEP} - Wire up VM_FLUSH_RESET_PERMS for arm64, allowing the core code to manage the permissions of executable vmalloc regions more strictly - Slight performance improvement by keeping softirqs enabled while touching the FPSIMD/SVE state (kernel_neon_begin/end) - Expose a couple of ARMv8.5 features to user (HWCAP): CondM (new XAFLAG and AXFLAG instructions for floating point comparison flags manipulation) and FRINT (rounding floating point numbers to integers) - Re-instate ARM64_PSEUDO_NMI support which was previously marked as BROKEN due to some bugs (now fixed) - Improve parking of stopped CPUs and implement an arm64-specific panic_smp_self_stop() to avoid warning on not being able to stop secondary CPUs during panic - perf: enable the ARM Statistical Profiling Extensions (SPE) on ACPI platforms - perf: DDR performance monitor support for iMX8QXP - cache_line_size() can now be set from DT or ACPI/PPTT if provided to cope with a system cache info not exposed via the CPUID registers - Avoid warning on hardware cache line size greater than ARCH_DMA_MINALIGN if the system is fully coherent - arm64 do_page_fault() and hugetlb cleanups - Refactor set_pte_at() to avoid redundant READ_ONCE(*ptep) - Ignore ACPI 5.1 FADTs reported as 5.0 (infer from the 'arm_boot_flags' introduced in 5.1) - CONFIG_RANDOMIZE_BASE now enabled in defconfig - Allow the selection of ARM64_MODULE_PLTS, currently only done via RANDOMIZE_BASE (and an erratum workaround), allowing modules to spill over into the vmalloc area - Make ZONE_DMA32 configurable * tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (54 commits) perf: arm_spe: Enable ACPI/Platform automatic module loading arm_pmu: acpi: spe: Add initial MADT/SPE probing ACPI/PPTT: Add function to return ACPI 6.3 Identical tokens ACPI/PPTT: Modify node flag detection to find last IDENTICAL x86/entry: Simplify _TIF_SYSCALL_EMU handling arm64: rename dump_instr as dump_kernel_instr arm64/mm: Drop [PTE|PMD]_TYPE_FAULT arm64: Implement panic_smp_self_stop() arm64: Improve parking of stopped CPUs arm64: Expose FRINT capabilities to userspace arm64: Expose ARMv8.5 CondM capability to userspace arm64: defconfig: enable CONFIG_RANDOMIZE_BASE arm64: ARM64_MODULES_PLTS must depend on MODULES arm64: bpf: do not allocate executable memory arm64/kprobes: set VM_FLUSH_RESET_PERMS on kprobe instruction pages arm64/mm: wire up CONFIG_ARCH_HAS_SET_DIRECT_MAP arm64: module: create module allocations without exec permissions arm64: Allow user selection of ARM64_MODULE_PLTS acpi/arm64: ignore 5.1 FADTs that are reported as 5.0 arm64: Allow selecting Pseudo-NMI again ...

ptrace: Fix ->ptracer_cred handling for PTRACE_TRACEME

2019-07-04T17:00:41Z

Fix two issues: When called for PTRACE_TRACEME, ptrace_link() would obtain an RCU reference to the parent's objective credentials, then give that pointer to get_cred(). However, the object lifetime rules for things like struct cred do not permit unconditionally turning an RCU reference into a stable reference. PTRACE_TRACEME records the parent's credentials as if the parent was acting as the subject, but that's not the case. If a malicious unprivileged child uses PTRACE_TRACEME and the parent is privileged, and at a later point, the parent process becomes attacker-controlled (because it drops privileges and calls execve()), the attacker ends up with control over two processes with a privileged ptrace relationship, which can be abused to ptrace a suid binary and obtain root privileges. Fix both of these by always recording the credentials of the process that is requesting the creation of the ptrace relationship: current_cred() can't change under us, and current is the proper subject for access control. This change is theoretically userspace-visible, but I am not aware of any code that it will actually break. Fixes: 64b875f7ac8a ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP") Signed-off-by: Jann Horn Acked-by: Oleg Nesterov Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2019-06-12T01:44:45Z

Pull ptrace fixes from Eric Biederman: "This is just two very minor fixes: - prevent ptrace from reading unitialized kernel memory found twice by syzkaller - restore a missing smp_rmb in ptrace_may_access and add comment tp it so it is not removed by accident again. Apologies for being a little slow about getting this to you, I am still figuring out how to develop with a little baby in the house" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: ptrace: restore smp_rmb() in __ptrace_may_access() signal/ptrace: Don't leak unitialized kernel memory with PTRACE_PEEK_SIGINFO

ptrace: restore smp_rmb() in __ptrace_may_access()

2019-06-11T20:08:28Z

Restore the read memory barrier in __ptrace_may_access() that was deleted a couple years ago. Also add comments on this barrier and the one it pairs with to explain why they're there (as far as I understand). Fixes: bfedb589252c ("mm: Add a user_ns owner to mm_struct and fix ptrace permission checks") Cc: stable@vger.kernel.org Acked-by: Kees Cook Acked-by: Oleg Nesterov Signed-off-by: Jann Horn Signed-off-by: Eric W. Biederman

ptrace: move clearing of TIF_SYSCALL_EMU flag to core

2019-06-05T16:51:17Z

While the TIF_SYSCALL_EMU is set in ptrace_resume independent of any architecture, currently only powerpc and x86 unset the TIF_SYSCALL_EMU flag in ptrace_disable which gets called from ptrace_detach. Let's move the clearing of TIF_SYSCALL_EMU flag to __ptrace_unlink which gets executed from ptrace_detach and also keep it along with or close to clearing of TIF_SYSCALL_TRACE. Cc: Paul Mackerras Cc: Michael Ellerman Cc: Thomas Gleixner Cc: Ingo Molnar Acked-by: Oleg Nesterov Signed-off-by: Sudeep Holla Signed-off-by: Catalin Marinas

signal/ptrace: Don't leak unitialized kernel memory with PTRACE_PEEK_SIGINFO

2019-05-30T11:38:29Z

Recently syzbot in conjunction with KMSAN reported that ptrace_peek_siginfo can copy an uninitialized siginfo to userspace. Inspecting ptrace_peek_siginfo confirms this. The problem is that off when initialized from args.off can be initialized to a negaive value. At which point the "if (off >= 0)" test to see if off became negative fails because off started off negative. Prevent the core problem by adding a variable found that is only true if a siginfo is found and copied to a temporary in preparation for being copied to userspace. Prevent args.off from being truncated when being assigned to off by testing that off is <= the maximum possible value of off. Convert off to an unsigned long so that we should not have to truncate args.off, we have well defined overflow behavior so if we add another check we won't risk fighting undefined compiler behavior, and so that we have a type whose maximum value is easy to test for. Cc: Andrei Vagin Cc: stable@vger.kernel.org Reported-by: syzbot+0d602a1b0d8c95bdf299@syzkaller.appspotmail.com Fixes: 84c751bd4aeb ("ptrace: add ability to retrieve signals without removing from a queue (v4)") Signed-off-by: "Eric W. Biederman"

treewide: Add SPDX license identifier for missed files

2019-05-21T08:50:45Z

Add SPDX license identifiers to all files which: - Have no license information of any form - Have EXPORT_.*_SYMBOL_GPL inside which was used in the initial scan/conversion to ignore the file These files fall under the project license, GPL v2 only. The resulting SPDX license identifier is: GPL-2.0-only Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

ptrace: take into account saved_sigmask in PTRACE{GET,SET}SIGMASK

2019-03-29T17:01:37Z

There are a few system calls (pselect, ppoll, etc) which replace a task sigmask while they are running in a kernel-space When a task calls one of these syscalls, the kernel saves a current sigmask in task->saved_sigmask and sets a syscall sigmask. On syscall-exit-stop, ptrace traps a task before restoring the saved_sigmask, so PTRACE_GETSIGMASK returns the syscall sigmask and PTRACE_SETSIGMASK does nothing, because its sigmask is replaced by saved_sigmask, when the task returns to user-space. This patch fixes this problem. PTRACE_GETSIGMASK returns saved_sigmask if it's set. PTRACE_SETSIGMASK drops the TIF_RESTORE_SIGMASK flag. Link: http://lkml.kernel.org/r/20181120060616.6043-1-avagin@gmail.com Fixes: 29000caecbe8 ("ptrace: add ability to get/set signal-blocked mask") Signed-off-by: Andrei Vagin Acked-by: Oleg Nesterov Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds