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Since 2.5.34 the code has had the potential to not allocate siginfo for SIGSTOP signals. Except for ptrace this is perfectly fine as only ptrace can use PTRACE_PEEK_SIGINFO and see what the contents of the delivered siginfo are. Users of PTRACE_PEEK_SIGINFO that care about the contents siginfo for SIGSTOP are rare, but they do exist. A seccomp self test has cared and lldb cares. Jack Andersen <jackoalan@gmail.com> writes: > The patch titled > `signal: Never allocate siginfo for SIGKILL or SIGSTOP` > created a regression for users of PTRACE_GETSIGINFO needing to > discern signals that were raised via the tgkill syscall. > > A notable user of this tgkill+ptrace combination is lldb while > debugging a multithreaded program. Without the ability to detect a > SIGSTOP originating from tgkill, lldb does not have a way to > synchronize on a per-thread basis and falls back to SIGSTOP-ing the > entire process. Everyone affected by this please note. The kernel can still fail to allocate a siginfo structure. The allocation is with GFP_KERNEL and is best effort only. If memory is tight when the signal allocation comes in this will fail to allocate a siginfo. So I strongly recommend looking at more robust solutions for synchronizing with a single thread such as PTRACE_INTERRUPT. Or if that does not work persuading your friendly local kernel developer to build the interface you need. Reported-by: Tycho Andersen <tycho@tycho.ws> Reported-by: Kees Cook <keescook@chromium.org> Reported-by: Jack Andersen <jackoalan@gmail.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: Christian Brauner <christian@brauner.io> Cc: stable@vger.kernel.org Fixes: f149b3155744 ("signal: Never allocate siginfo for SIGKILL or SIGSTOP") Fixes: 6dfc88977e42 ("[PATCH] shared thread signals") History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.