2019-05-22 19:18:24

by Bharath Vedartham

Subject: [PATCH] 9p/cache.c: Fix memory leak in v9fs_cache_session_get_cookie

v9fs_cache_session_get_cookie assigns a random cachetag to
v9ses->cachetag, if the cachetag is not assigned previously.

v9fs_random_cachetag allocates memory to v9ses->cachetag with kmalloc
and uses scnprintf to fill it up with a cachetag.

But if scnprintf fails, v9ses->cachetag is not freed in the current code causing a memory leak.

Fix this by freeing v9ses->cachetag it v9fs_random_cachetag fails.

This was reported by syzbot, the link to the report is below:
https://syzkaller.appspot.com/bug?id=f012bdf297a7a4c860c38a88b44fbee43fd9bbf3

Reported-by: [email protected]
Signed-off-by: Bharath Vedartham <[email protected]>
---
fs/9p/cache.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/9p/cache.c b/fs/9p/cache.c
index 9eb3470..4463b91 100644
--- a/fs/9p/cache.c
+++ b/fs/9p/cache.c
@@ -66,6 +66,7 @@ void v9fs_cache_session_get_cookie(struct v9fs_session_info *v9ses)
if (!v9ses->cachetag) {
if (v9fs_random_cachetag(v9ses) < 0) {
v9ses->fscache = NULL;
+ kfree(v9ses->cachetag);
return;
}
}
--
2.7.4

2019-05-22 20:06:20

by Dominique Martinet

Subject: Re: [PATCH] 9p/cache.c: Fix memory leak in v9fs_cache_session_get_cookie

Bharath Vedartham wrote on Thu, May 23, 2019:
> v9fs_cache_session_get_cookie assigns a random cachetag to
> v9ses->cachetag, if the cachetag is not assigned previously.
>
> v9fs_random_cachetag allocates memory to v9ses->cachetag with kmalloc
> and uses scnprintf to fill it up with a cachetag.
>
> But if scnprintf fails, v9ses->cachetag is not freed in the current code causing a memory leak.
>
> Fix this by freeing v9ses->cachetag it v9fs_random_cachetag fails.
>
> This was reported by syzbot, the link to the report is below:
> https://syzkaller.appspot.com/bug?id=f012bdf297a7a4c860c38a88b44fbee43fd9bbf3
>
> Reported-by: [email protected]
> Signed-off-by: Bharath Vedartham <[email protected]>
> ---
> fs/9p/cache.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/9p/cache.c b/fs/9p/cache.c
> index 9eb3470..4463b91 100644
> --- a/fs/9p/cache.c
> +++ b/fs/9p/cache.c
> @@ -66,6 +66,7 @@ void v9fs_cache_session_get_cookie(struct v9fs_session_info *v9ses)
> if (!v9ses->cachetag) {
> if (v9fs_random_cachetag(v9ses) < 0) {
> v9ses->fscache = NULL;
> + kfree(v9ses->cachetag);

I would also reset v9ses->cachetag to NULL just in case,
v9fs_cache_session_get_cookie will use v9ses->cachetag as it is if it is
not null and you were leaving an invalid pointer there

I do not see any reason it could be called multiple times but
v9fs_cache_session_get_cookie does not return any error (void function)
so something later on could try to use that cachetag incorrectly later
on

Thanks,
--
Dominique