Re: [PATCH] tomoyo: Avoid potential null pointer access

[Zheng Zengkai]

Hello, Tetsuo

Got it , Thank you for your explanation.
Hello, Zheng.

Thank you for a patch, but I won't apply this patch.
Expected behavior is that tomoyo_warn_oom() is called
if tomoyo_memory_ok() is called with entry == NULL.

Adding __GFP_NOWARN might be OK, but returning without tomoyo_warn_oom() is NG.

On 2020/11/25 21:10, Zheng Zengkai wrote:
Calls to kzalloc() should be null-checked in order to avoid
any potential failures or unnecessary code execution.
Fix this by adding null checks for _entry_ right after allocation.

Fixes: 57c2590fb7fd ("TOMOYO: Update profile structure")
Reported-by: Hulk Robot <hul...@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzeng...@huawei.com>
Nacked-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>

As your say,  I found the function tomoyo_assign_namespace( )

in security/tomoyo/domain.c has the similar situation,

Can I add __GFP_NOWARN for both and remove the null check for _entry_ in 
tomoyo_assign_namespace( )?

diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index 4bee32bfe16d..bc54d3c8c70a 100644
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -498,7 +498,7 @@ static struct tomoyo_profile *tomoyo_assign_profile
        ptr = ns->profile_ptr[profile];
        if (ptr)
                return ptr;
-       entry = kzalloc(sizeof(*entry), GFP_NOFS);
+       entry = kzalloc(sizeof(*entry), GFP_NOFS | __GFP_NOWARN);
        if (mutex_lock_interruptible(&tomoyo_policy_lock))
                goto out;
        ptr = ns->profile_ptr[profile];
diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index dc4ecc0b2038..c6e5cc5cc7cd 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -473,9 +473,7 @@ struct tomoyo_policy_namespace 
*tomoyo_assign_namespace(const char *domainname)
                return ptr;
        if (len >= TOMOYO_EXEC_TMPSIZE - 10 || 
!tomoyo_domain_def(domainname))
                return NULL;
-       entry = kzalloc(sizeof(*entry) + len + 1, GFP_NOFS);
-       if (!entry)
-               return NULL;
+       entry = kzalloc(sizeof(*entry) + len + 1, GFP_NOFS | __GFP_NOWARN);
        if (mutex_lock_interruptible(&tomoyo_policy_lock))
                goto out;
        ptr = tomoyo_find_namespace(domainname, len);

---
  security/tomoyo/common.c | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index 4bee32bfe16d..99b4fafcb100 100644
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -499,6 +499,8 @@ static struct tomoyo_profile *tomoyo_assign_profile
        if (ptr)
                return ptr;
        entry = kzalloc(sizeof(*entry), GFP_NOFS);
+       if (!entry)
+               return NULL;
        if (mutex_lock_interruptible(&tomoyo_policy_lock))
                goto out;
        ptr = ns->profile_ptr[profile];

.