From: Christoph Hellwig <hch@xxxxxx> Subject: exec: use force_uaccess_begin during exec and exit Both exec and exit want to ensure that the uaccess routines actually do access user pointers. Use the newly added force_uaccess_begin helper instead of an open coded set_fs for that to prepare for kernel builds where set_fs() does not exist. Link: http://lkml.kernel.org/r/20200710135706.537715-7-hch@xxxxxx Signed-off-by: Christoph Hellwig <hch@xxxxxx> Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Nick Hu <nickhu@xxxxxxxxxxxxx> Cc: Greentime Hu <green.hu@xxxxxxxxx> Cc: Vincent Chen <deanbo422@xxxxxxxxx> Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/exec.c | 7 ++++++- kernel/exit.c | 2 +- 2 files changed, 7 insertions(+), 2 deletions(-) --- a/fs/exec.c~exec-use-force_uaccess_begin-during-exec-and-exit +++ a/fs/exec.c @@ -1402,7 +1402,12 @@ int begin_new_exec(struct linux_binprm * if (retval) goto out_unlock; - set_fs(USER_DS); + /* + * Ensure that the uaccess routines can actually operate on userspace + * pointers: + */ + force_uaccess_begin(); + me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD | PF_NOFREEZE | PF_NO_SETAFFINITY); flush_thread(); --- a/kernel/exit.c~exec-use-force_uaccess_begin-during-exec-and-exit +++ a/kernel/exit.c @@ -732,7 +732,7 @@ void __noreturn do_exit(long code) * mm_release()->clear_child_tid() from writing to a user-controlled * kernel address. */ - set_fs(USER_DS); + force_uaccess_begin(); if (unlikely(in_atomic())) { pr_info("note: %s[%d] exited with preempt_count %d\n", _
