releases/5.11.3/proc-use-kvzalloc-for-our-kernel-buffer.patch

From f0b6742cee54097003e23e28df53f415e9340fe2 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Thu, 25 Feb 2021 17:20:49 -0800
Subject: proc: use kvzalloc for our kernel buffer

From: Josef Bacik <josef@toxicpanda.com>

[ Upstream commit 4508943794efdd94171549c0bd52810e2f4ad9fe ]

Since

  sysctl: pass kernel pointers to ->proc_handler

we have been pre-allocating a buffer to copy the data from the proc
handlers into, and then copying that to userspace.  The problem is this
just blindly kzalloc()'s the buffer size passed in from the read, which in
the case of our 'cat' binary was 64kib.  Order-4 allocations are not
awesome, and since we can potentially allocate up to our maximum order, so
use kvzalloc for these buffers.

[willy@infradead.org: changelog tweaks]

Link: https://lkml.kernel.org/r/6345270a2c1160b89dd5e6715461f388176899d1.1612972413.git.josef@toxicpanda.com
Fixes: 32927393dc1c ("sysctl: pass kernel pointers to ->proc_handler")
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
CC: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/proc/proc_sysctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index d2018f70d1fae..070d2df8ab9cf 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -571,7 +571,7 @@ static ssize_t proc_sys_call_handler(struct kiocb *iocb, struct iov_iter *iter,
 	error = -ENOMEM;
 	if (count >= KMALLOC_MAX_SIZE)
 		goto out;
-	kbuf = kzalloc(count + 1, GFP_KERNEL);
+	kbuf = kvzalloc(count + 1, GFP_KERNEL);
 	if (!kbuf)
 		goto out;
 
@@ -600,7 +600,7 @@ static ssize_t proc_sys_call_handler(struct kiocb *iocb, struct iov_iter *iter,
 
 	error = count;
 out_free_buf:
-	kfree(kbuf);
+	kvfree(kbuf);
 out:
 	sysctl_head_finish(head);
 
-- 
2.27.0