linux-kernel - [PATCH 4.19 092/113] proc: use down_read_killable mmap_sem for /proc/pid/map

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Date:   Mon, 29 Jul 2019 21:22:59 +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>,
        Roman Gushchin <guro@...com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Michal Hocko <mhocko@...e.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Koutný <mkoutny@...e.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 092/113] proc: use down_read_killable mmap_sem for /proc/pid/map_files

[ Upstream commit cd9e2bb8271c971d9f37c722be2616c7f8ba0664 ]

Do not remain stuck forever if something goes wrong.  Using a killable
lock permits cleanup of stuck tasks and simplifies investigation.

It seems ->d_revalidate() could return any error (except ECHILD) to abort
validation and pass error as result of lookup sequence.

[akpm@...ux-foundation.org: fix proc_map_files_lookup() return value, per Andrei]
Link: http://lkml.kernel.org/r/156007493995.3335.9595044802115356911.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Reviewed-by: Roman Gushchin <guro@...com>
Reviewed-by: Cyrill Gorcunov <gorcunov@...il.com>
Reviewed-by: Kirill Tkhai <ktkhai@...tuozzo.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Michal Koutný <mkoutny@...e.com>
Cc: Oleg Nesterov <oleg@...hat.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>
---
 fs/proc/base.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index f999e8bd3771..a7fbda72afeb 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1960,9 +1960,12 @@ static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
 		goto out;
 
 	if (!dname_to_vma_addr(dentry, &vm_start, &vm_end)) {
-		down_read(&mm->mmap_sem);
-		exact_vma_exists = !!find_exact_vma(mm, vm_start, vm_end);
-		up_read(&mm->mmap_sem);
+		status = down_read_killable(&mm->mmap_sem);
+		if (!status) {
+			exact_vma_exists = !!find_exact_vma(mm, vm_start,
+							    vm_end);
+			up_read(&mm->mmap_sem);
+		}
 	}
 
 	mmput(mm);
@@ -2008,8 +2011,11 @@ static int map_files_get_link(struct dentry *dentry, struct path *path)
 	if (rc)
 		goto out_mmput;
 
+	rc = down_read_killable(&mm->mmap_sem);
+	if (rc)
+		goto out_mmput;
+
 	rc = -ENOENT;
-	down_read(&mm->mmap_sem);
 	vma = find_exact_vma(mm, vm_start, vm_end);
 	if (vma && vma->vm_file) {
 		*path = vma->vm_file->f_path;
@@ -2105,7 +2111,11 @@ static struct dentry *proc_map_files_lookup(struct inode *dir,
 	if (!mm)
 		goto out_put_task;
 
-	down_read(&mm->mmap_sem);
+	result = ERR_PTR(-EINTR);
+	if (down_read_killable(&mm->mmap_sem))
+		goto out_put_mm;
+
+	result = ERR_PTR(-ENOENT);
 	vma = find_exact_vma(mm, vm_start, vm_end);
 	if (!vma)
 		goto out_no_vma;
@@ -2116,6 +2126,7 @@ static struct dentry *proc_map_files_lookup(struct inode *dir,
 
 out_no_vma:
 	up_read(&mm->mmap_sem);
+out_put_mm:
 	mmput(mm);
 out_put_task:
 	put_task_struct(task);
@@ -2157,7 +2168,12 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
 	mm = get_task_mm(task);
 	if (!mm)
 		goto out_put_task;
-	down_read(&mm->mmap_sem);
+
+	ret = down_read_killable(&mm->mmap_sem);
+	if (ret) {
+		mmput(mm);
+		goto out_put_task;
+	}
 
 	nr_files = 0;
 
-- 
2.20.1