[PATCH 4.9 42/60] proc: Avoid mixing integer types in mem_rw()

Greg Kroah-Hartman
2021-07-26T15:45:06Z

From: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>

[ 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@canonical.com
Reviewed-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Souza Cascardo <cascardo@canonical.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
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/base.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 0368ff9335cb..886e408f4769 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -867,7 +867,7 @@ static ssize_t mem_rw(struct file *file, char __user *buf,
flags |= FOLL_WRITE;

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