From fe69d560b5bd9ec77b5d5749bd7027344daef47e Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Fri, 23 Apr 2021 10:29:59 +0200 Subject: kernel/fork: always deny write access to current MM exe_file MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit We want to remove VM_DENYWRITE only currently only used when mapping the executable during exec. During exec, we already deny_write_access() the executable, however, after exec completes the VMAs mapped with VM_DENYWRITE effectively keeps write access denied via deny_write_access(). Let's deny write access when setting or replacing the MM exe_file. With this change, we can remove VM_DENYWRITE for mapping executables. Make set_mm_exe_file() return an error in case deny_write_access() fails; note that this should never happen, because exec code does a deny_write_access() early and keeps write access denied when calling set_mm_exe_file. However, it makes the code easier to read and makes set_mm_exe_file() and replace_mm_exe_file() look more similar. This represents a minor user space visible change: sys_prctl(PR_SET_MM_MAP/EXE_FILE) can now fail if the file is already opened writable. Also, after sys_prctl(PR_SET_MM_MAP/EXE_FILE) the file cannot be opened writable. Note that we can already fail with -EACCES if the file doesn't have execute permissions. Acked-by: "Eric W. Biederman" Acked-by: Christian König Signed-off-by: David Hildenbrand --- fs/exec.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'fs/exec.c') diff --git a/fs/exec.c b/fs/exec.c index 38f63451b928..9294049f5487 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1270,7 +1270,9 @@ int begin_new_exec(struct linux_binprm * bprm) * not visibile until then. This also enables the update * to be lockless. */ - set_mm_exe_file(bprm->mm, bprm->file); + retval = set_mm_exe_file(bprm->mm, bprm->file); + if (retval) + goto out; /* If the binary is not readable then enforce mm->dumpable=0 */ would_dump(bprm, bprm->file); -- cgit v1.2.3-70-g09d2