From 034dd340b08be1f2f0477ad16131d609f9dbd53c Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 30 Aug 2026 09:22:00 -0700 Subject: Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace Pull tracing fixes from Steven Rostedt: - Fix error output of boot instance creation failure Currently if a boot instance creation fails, instead of printing out the name of the instance that failed, it prints "(null)". That is because it prints "cur_str" that had already been processed by strsep(). Print the saved name instead. While at it, print the error code of the failure. - Fix use-after-free for same named historgrams Histograms can be named so that they can be used in multiple events. But if the named histogram has a variable attached, the second event that uses the named histogram which duplicates it and needs to free the original after duplication leaves the old variable in place and still visible. If another histogram uses than variable, it will use the stale one which will try to reference the freed duplicate histogram and crash the kernel. Free the duplicate variables along with the duplicated histogram data. - Check return value of kthread_run() in event self test The events self tests uses a kthread for testing but does not check if it succeeded in creating a kthread. If the kthread creation were to fail, the code will still try to call kthread_stop() on the error returned. - Fix race between reading trace_pipe and updating subbuffer size If a user is reading the trace_pipe file at the same time they update the ring buffer sub-buffer size, can cause the trace_pipe read to read stale data. Add trace_access_lock() around updating the ring buffer sub-buffer size. - Fix eventfs_inode on failure path in creation of the events directory In the creation of the "events" directory, if after allocating the eventfs_inode a failure is detected, it calls cleanup_ei() which calls free_ei(). The free_ei() will test if eventfs_inode being freed has no children. It is a bug if it does. But on the failure case of the creation of the "events" directory, the children lists have not yet been initialized and the free will trigger a warning because list_empty() on an uninitialized list returns false. Move the initialization into init_ei() where it makes more sense and makes sure that a created eventfs_inode has its lists initialized upon creation. - Check return value of kthread_run() in ftrace direct sample code The sample code that shows how to use the ftrace direct calls does not test the return of kthread_run() to see if it succeeds. Return a failure if the kthread_run() doesn't succeed. - Clear user events state on fork in case of alloc failure On fork, the child gets a pointer to the parent's user events state. It makes a copy of it then updates the child's pointer to it. But if the allocation fails, the duplication function leaves the child with a pointer to its parent's descriptor. When the child cleans up its data, it will free the parent's descriptor while the parent is still using it. In the duplication function, set the child's user_event_mm to NULL before testing if the allocation succeeded, and when it exits it will not free the parent's descriptor. - Fix retry exhaustion in simple ring buffer reader swap simple_ring_buffer_swap_reader_page() starts with retry set to 8 and post-decrements it only after a failed link replacement. On the final attempt, a successful replacement leaves retry at zero, while a failed replacement leaves it at -1. But the check for success expects the retry value to be non-zero and exits with an error on zero. This is the opposite result. Fix it. - Fail nicely when the remote swap_reader_page() returns an error Currently, if the swap_reader_page() of a remote buffer fails, it triggers a WARN_ON_ONCE() and continues normally. Instead, have it exit with an error and a pr_warn() print instead of a full WARNING. * tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: ring-buffer: Stop remote reader update when page swap fails tracing: Fix retry exhaustion in simple ring buffer reader swap tracing/user_events: Clear copied tracing state before fork duplication samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify eventfs: Initialize ei->children and ei->list in init_ei() tracing: Fix use-after-free in trace_pipe read on sub-buffer order change tracing: Fix crash passing ERR_PTR to kthread_stop() tracing: Fix use-after-free with same-name named triggers tracing: Fix logged instance name on creation failure --- Documentation/security/sak.rst | 91 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 91 insertions(+) create mode 100644 Documentation/security/sak.rst (limited to 'Documentation/security/sak.rst') diff --git a/Documentation/security/sak.rst b/Documentation/security/sak.rst new file mode 100644 index 000000000..260e1d368 --- /dev/null +++ b/Documentation/security/sak.rst @@ -0,0 +1,91 @@ +========================================= +Linux Secure Attention Key (SAK) handling +========================================= + +:Date: 18 March 2001 +:Author: Andrew Morton + +An operating system's Secure Attention Key is a security tool which is +provided as protection against trojan password capturing programs. It +is an undefeatable way of killing all programs which could be +masquerading as login applications. Users need to be taught to enter +this key sequence before they log in to the system. + +From the PC keyboard, Linux has two similar but different ways of +providing SAK. One is the ALT-SYSRQ-K sequence. You shouldn't use +this sequence. It is only available if the kernel was compiled with +sysrq support. + +The proper way of generating a SAK is to define the key sequence using +``loadkeys``. This will work whether or not sysrq support is compiled +into the kernel. + +SAK works correctly when the keyboard is in raw mode. This means that +once defined, SAK will kill a running X server. If the system is in +run level 5, the X server will restart. This is what you want to +happen. + +What key sequence should you use? Well, CTRL-ALT-DEL is used to reboot +the machine. CTRL-ALT-BACKSPACE is magical to the X server. We'll +choose CTRL-ALT-PAUSE. + +In your rc.sysinit (or rc.local) file, add the command:: + + echo "control alt keycode 101 = SAK" | /bin/loadkeys + +And that's it! Only the superuser may reprogram the SAK key. + + +.. note:: + + 1. Linux SAK is said to be not a "true SAK" as is required by + systems which implement C2 level security. This author does not + know why. + + + 2. On the PC keyboard, SAK kills all applications which have + /dev/console opened. + + Unfortunately this includes a number of things which you don't + actually want killed. This is because these applications are + incorrectly holding /dev/console open. Be sure to complain to your + Linux distributor about this! + + You can identify processes which will be killed by SAK with the + command:: + + # ls -l /proc/[0-9]*/fd/* | grep console + l-wx------ 1 root root 64 Mar 18 00:46 /proc/579/fd/0 -> /dev/console + + Then:: + + # ps aux|grep 579 + root 579 0.0 0.1 1088 436 ? S 00:43 0:00 gpm -t ps/2 + + So ``gpm`` will be killed by SAK. This is a bug in gpm. It should + be closing standard input. You can work around this by finding the + initscript which launches gpm and changing it thusly: + + Old:: + + daemon gpm + + New:: + + daemon gpm < /dev/null + + Vixie cron also seems to have this problem, and needs the same treatment. + + Also, one prominent Linux distribution has the following three + lines in its rc.sysinit and rc scripts:: + + exec 3<&0 + exec 4>&1 + exec 5>&2 + + These commands cause **all** daemons which are launched by the + initscripts to have file descriptors 3, 4 and 5 attached to + /dev/console. So SAK kills them all. A workaround is to simply + delete these lines, but this may cause system management + applications to malfunction - test everything well. + -- cgit v1.3.1