From d284770333373625457fb369ddcbcbedeb1312ff Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 20 Aug 2017 13:26:27 -0700 Subject: [PATCH] Sanitize 'move_pages()' permission checks commit 197e7e521384a23b9e585178f3f11c9fa08274b9 upstream. The 'move_paghes()' system call was introduced long long ago with the same permission checks as for sending a signal (except using CAP_SYS_NICE instead of CAP_SYS_KILL for the overriding capability). That turns out to not be a great choice - while the system call really only moves physical page allocations around (and you need other capabilities to do a lot of it), you can check the return value to map out some the virtual address choices and defeat ASLR of a binary that still shares your uid. So change the access checks to the more common 'ptrace_may_access()' model instead. This tightens the access checks for the uid, and also effectively changes the CAP_SYS_NICE check to CAP_SYS_PTRACE, but it's unlikely that anybody really _uses_ this legacy system call any more (we hav ebetter NUMA placement models these days), so I expect nobody to notice. Famous last words. Change-Id: I033691ba22e3bd606e61e94d54c4f6def301b8a8 Reported-by: Otto Ebeling Acked-by: Eric W. Biederman Cc: Willy Tarreau Signed-off-by: Linus Torvalds [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings --- mm/migrate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/migrate.c b/mm/migrate.c index 755277966a54..a84e20e7098a 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1424,7 +1424,7 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages, * Check if this process has the right to modify the specified * process. Use the regular "ptrace_may_access()" checks. */ - if (!ptrace_may_access(task, PTRACE_MODE_READ)) { + if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { rcu_read_unlock(); err = -EPERM; goto out;