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Message-Id: <20190729190808.252237041@linuxfoundation.org>
Date: Mon, 29 Jul 2019 21:22:40 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org,
Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
Michal Koutný <mkoutny@...e.com>,
Oleg Nesterov <oleg@...hat.com>,
Michal Hocko <mhocko@...e.com>,
Alexey Dobriyan <adobriyan@...il.com>,
Matthew Wilcox <willy@...radead.org>,
Cyrill Gorcunov <gorcunov@...il.com>,
Kirill Tkhai <ktkhai@...tuozzo.com>,
Al Viro <viro@...iv.linux.org.uk>,
Roman Gushchin <guro@...com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.2 164/215] mm: use down_read_killable for locking mmap_sem in access_remote_vm
[ Upstream commit 1e426fe28261b03f297992e89da3320b42816f4e ]
This function is used by ptrace and proc files like /proc/pid/cmdline and
/proc/pid/environ.
Access_remote_vm never returns error codes, all errors are ignored and
only size of successfully read data is returned. So, if current task was
killed we'll simply return 0 (bytes read).
Mmap_sem could be locked for a long time or forever if something goes
wrong. Using a killable lock permits cleanup of stuck tasks and
simplifies investigation.
Link: http://lkml.kernel.org/r/156007494202.3335.16782303099589302087.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Reviewed-by: Michal Koutný <mkoutny@...e.com>
Acked-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Cyrill Gorcunov <gorcunov@...il.com>
Cc: Kirill Tkhai <ktkhai@...tuozzo.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Roman Gushchin <guro@...com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
mm/memory.c | 4 +++-
mm/nommu.c | 3 ++-
2 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index ddf20bd0c317..9a4401d21e94 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4349,7 +4349,9 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
void *old_buf = buf;
int write = gup_flags & FOLL_WRITE;
- down_read(&mm->mmap_sem);
+ if (down_read_killable(&mm->mmap_sem))
+ return 0;
+
/* ignore errors, just check how much was successfully transferred */
while (len) {
int bytes, ret, offset;
diff --git a/mm/nommu.c b/mm/nommu.c
index d8c02fbe03b5..b2823519f8cd 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1792,7 +1792,8 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
struct vm_area_struct *vma;
int write = gup_flags & FOLL_WRITE;
- down_read(&mm->mmap_sem);
+ if (down_read_killable(&mm->mmap_sem))
+ return 0;
/* the access must start within one of the target process's mappings */
vma = find_vma(mm, addr);
--
2.20.1
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