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SubjectRe: [PATCH RESEND] exec: don't force_sigsegv processes with a pending fatal signal
Hi Ivan,

2018-07-31 1:56 GMT+01:00 Ivan Delalande <colona@arista.com>:
> We were seeing unexplained segfaults in coreutils processes and other
> basic utilities that we tracked down to binfmt_elf failing to load
> segments for ld.so. Digging further, the actual problem seems to occur
> when a process gets sigkilled while it is still being loaded by the
> kernel. In our case when _do_page_fault goes for a retry it will return
> early as it first checks for fatal_signal_pending(), so load_elf_interp
> also returns with error and as a result search_binary_handler will
> force_sigsegv() which is pretty confusing as nothing actually failed
> here.
>
> Fixes: 19d860a140be ("handle suicide on late failure exits in execve() in search_binary_handler()")
> Reference: https://lkml.org/lkml/2013/2/14/5
> Signed-off-by: Ivan Delalande <colona@arista.com>

+Cc: Oleg Nesterov <oleg@redhat.com>
+Cc: Andy Lutomirski <luto@kernel.org>

> ---
> fs/exec.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index bdd0eacefdf5..6e8007edbb2d 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1656,7 +1656,8 @@ int search_binary_handler(struct linux_binprm *bprm)
> if (retval < 0 && !bprm->mm) {
> /* we got to flush_old_exec() and failed after it */
> read_unlock(&binfmt_lock);
> - force_sigsegv(SIGSEGV, current);
> + if (!fatal_signal_pending(current))
> + force_sigsegv(SIGSEGV, current);

I would suggest to add something like:
: if (print_fatal_signals)
: pr_info("load_binary() failed: %d\n", retval);

It was interesting to catch that it actually segfaults during loading,
probably will save someone a couple of minutes too ;-)

> return retval;
> }
> if (retval != -ENOEXEC || !bprm->file) {

Thanks,
Dmitry

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