[PATCH AUTOSEL 4.14 14/16] smackfs: restrict bytes count in smackfs write functions

Sasha Levin
2021-02-24T14:17:54Z

From: Sabyrzhan Tasbolatov <snovitoll@gmail.com>

[ Upstream commit 7ef4c19d245f3dc233fd4be5acea436edd1d83d8 ]

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 than PAGE_SIZE.

Per smackfs doc, smk_write_net4addr accepts any label or -CIPSO,
smk_write_net6addr accepts any label or -DELETE. I couldn't find
any general rule for other label lengths except SMK_LABELLEN,
SMK_LONGLABEL, SMK_CIPSOMAX which are documented.

Let's constrain, in general, smackfs label lengths for PAGE_SIZE.
Although fuzzer crashes write to smackfs/netlabel on 0x400000 length.

Here is a quick way to reproduce the WARNING:
python -c "print('A' * 0x400000)" > /sys/fs/smackfs/netlabel

Reported-by: syzbot+a71a442385a0b2815497@syzkaller.appspotmail.com
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
security/smack/smackfs.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index accd3846f1e3e..4f8c1a272df07 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -1191,7 +1191,7 @@ 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 > PAGE_SIZE - 1)
return -EINVAL;

data = memdup_user_nul(buf, count);
@@ -1451,7 +1451,7 @@ 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 > PAGE_SIZE - 1)
return -EINVAL;

data = memdup_user_nul(buf, count);
@@ -1858,6 +1858,10 @@ static ssize_t smk_write_ambient(struct file *file, const char __user *buf,
if (!smack_privileged(CAP_MAC_ADMIN))
return -EPERM;

+ /* Enough data must be present */
+ if (count == 0 || count > PAGE_SIZE)
+ return -EINVAL;
+
data = memdup_user_nul(buf, count);
if (IS_ERR(data))
return PTR_ERR(data);
@@ -2029,6 +2033,9 @@ static ssize_t smk_write_onlycap(struct file *file, const char __user *buf,
if (!smack_privileged(CAP_MAC_ADMIN))
return -EPERM;

+ if (count > PAGE_SIZE)
+ return -EINVAL;
+
data = memdup_user_nul(buf, count);
if (IS_ERR(data))
return PTR_ERR(data);
@@ -2116,6 +2123,9 @@ static ssize_t smk_write_unconfined(struct file *file, const char __user *buf,
if (!smack_privileged(CAP_MAC_ADMIN))
return -EPERM;

+ if (count > PAGE_SIZE)
+ return -EINVAL;
+
data = memdup_user_nul(buf, count);
if (IS_ERR(data))
return PTR_ERR(data);
@@ -2669,6 +2679,10 @@ static ssize_t smk_write_syslog(struct file *file, const char __user *buf,
if (!smack_privileged(CAP_MAC_ADMIN))
return -EPERM;

+ /* Enough data must be present */
+ if (count == 0 || count > PAGE_SIZE)
+ return -EINVAL;
+
data = memdup_user_nul(buf, count);
if (IS_ERR(data))
return PTR_ERR(data);
@@ -2761,10 +2775,13 @@ static ssize_t smk_write_relabel_self(struct file *file, const char __user *buf,
return -EPERM;

/*
+ * No partial write.
* Enough data must be present.
*/
if (*ppos != 0)
return -EINVAL;
+ if (count == 0 || count > PAGE_SIZE)
+ return -EINVAL;

data = memdup_user_nul(buf, count);
if (IS_ERR(data))
--
2.27.0