[PATCH] smackfs: restrict bytes count in smackfs write functions

From: Sabyrzhan Tasbolatov
Date: Sun Jan 24 2021 - 09:37:27 EST


syzbot found WARNINGs in several smackfs write operations where
bytes count is passed to memdup_user_nul which exceeds
GFP MAX_ORDER. Check count size if bigger SMK_LONGLABEL,
for smk_write_syslog if bigger than PAGE_SIZE - 1.

Reported-by: syzbot+a71a442385a0b2815497@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx>
---
security/smack/smackfs.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 5d44b7d258ef..88678c6f1b8c 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -1167,7 +1167,7 @@ static ssize_t smk_write_net4addr(struct file *file, const char __user *buf,
return -EPERM;
if (*ppos != 0)
return -EINVAL;
- if (count < SMK_NETLBLADDRMIN)
+ if (count < SMK_NETLBLADDRMIN || count > SMK_LONGLABEL)
return -EINVAL;

data = memdup_user_nul(buf, count);
@@ -1427,7 +1427,7 @@ static ssize_t smk_write_net6addr(struct file *file, const char __user *buf,
return -EPERM;
if (*ppos != 0)
return -EINVAL;
- if (count < SMK_NETLBLADDRMIN)
+ if (count < SMK_NETLBLADDRMIN || count > SMK_LONGLABEL)
return -EINVAL;

data = memdup_user_nul(buf, count);
@@ -2647,6 +2647,8 @@ static ssize_t smk_write_syslog(struct file *file, const char __user *buf,

if (!smack_privileged(CAP_MAC_ADMIN))
return -EPERM;
+ if (count > PAGE_SIZE - 1)
+ return -EINVAL;

data = memdup_user_nul(buf, count);
if (IS_ERR(data))
@@ -2744,6 +2746,8 @@ static ssize_t smk_write_relabel_self(struct file *file, const char __user *buf,
*/
if (*ppos != 0)
return -EINVAL;
+ if (count > SMK_LONGLABEL)
+ return -EINVAL;

data = memdup_user_nul(buf, count);
if (IS_ERR(data))
--
2.25.1