[PATCH 5.10 105/167] proc: Avoid mixing integer types in mem_rw()

[Greg Kroah-Hartman]

From: Marcelo Henrique Cerri <marcelo.cerri@xxxxxxxxxxxxx>

[ Upstream commit d238692b4b9f2c36e35af4c6e6f6da36184aeb3e ]

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.

Link: https://lkml.kernel.org/r/20210512125215.3348316-1-marcelo.cerri@xxxxxxxxxxxxx
Reviewed-by: David Disseldorp <ddiss@xxxxxxx>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@xxxxxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 df9b17dd92cb..5d52aea8d7e7 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -855,7 +855,7 @@ 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;
-- 
2.30.2