linux-kernel - [PATCH] proc: Avoid mixing integer types in mem

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Date:   Wed, 12 May 2021 09:52:12 -0300
From:   Marcelo Henrique Cerri <marcelo.cerri@...onical.com>
To:     linux-fsdevel@...r.kernel.org
Cc:     Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        David Disseldorp <ddiss@...e.de>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Michel Lespinasse <walken@...gle.com>,
        Helge Deller <deller@....de>, Oleg Nesterov <oleg@...hat.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] proc: Avoid mixing integer types in mem_rw()

Use size_t when capping the count argument received by mem_rw(). Since
count is size_t, using min_t(int, ...) can lead to a negative value
that will later be passed to access_remote_vm(), which can cause
unexpected behavior.

Since we are capping the value to at maximum PAGE_SIZE, the conversion
from size_t to int when passing it to access_remote_vm() as "len"
shouldn't be a problem.

Reviewed-by: David Disseldorp <ddiss@...e.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@...onical.com>
---
 fs/proc/base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 3851bfcdba56..8dbc6a1aaadb 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -854,7 +854,7 @@ static ssize_t mem_rw(struct file *file, char __user *buf,
 	flags = FOLL_FORCE | (write ? FOLL_WRITE : 0);
 
 	while (count > 0) {
-		int this_len = min_t(int, count, PAGE_SIZE);
+		size_t this_len = min_t(size_t, count, PAGE_SIZE);
 
 		if (write && copy_from_user(page, buf, this_len)) {
 			copied = -EFAULT;
-- 
2.25.1