| Message ID | 1563625366-3602-1-git-send-email-wang6495@umn.edu |
|---|---|
| State | Accepted |
| Delegated to: | Pablo Neira |
| Headers | show |
| Series | netfilter: ebtables: compat: fix a memory leak bug | expand |
Wenwen Wang <wang6495@umn.edu> wrote: > From: Wenwen Wang <wenwen@cs.uga.edu> > > In compat_do_replace(), a temporary buffer is allocated through vmalloc() > to hold entries copied from the user space. The buffer address is firstly > saved to 'newinfo->entries', and later on assigned to 'entries_tmp'. Then > the entries in this temporary buffer is copied to the internal kernel > structure through compat_copy_entries(). If this copy process fails, > compat_do_replace() should be terminated. However, the allocated temporary > buffer is not freed on this path, leading to a memory leak. > > To fix the bug, free the buffer before returning from compat_do_replace(). > > Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu> Reviewed-by: Florian Westphal <fw@strlen.de>
On Sat, Jul 20, 2019 at 07:22:45AM -0500, Wenwen Wang wrote: > From: Wenwen Wang <wenwen@cs.uga.edu> > > In compat_do_replace(), a temporary buffer is allocated through vmalloc() > to hold entries copied from the user space. The buffer address is firstly > saved to 'newinfo->entries', and later on assigned to 'entries_tmp'. Then > the entries in this temporary buffer is copied to the internal kernel > structure through compat_copy_entries(). If this copy process fails, > compat_do_replace() should be terminated. However, the allocated temporary > buffer is not freed on this path, leading to a memory leak. > > To fix the bug, free the buffer before returning from compat_do_replace(). Applied, thanks.
Nice catch. The code that exists is confusing due to newinfo->entries being overwritten and then freed in the existing code path as you state in your commit log. * Wenwen Wang <wang6495@umn.edu> [190720 08:23]: > From: Wenwen Wang <wenwen@cs.uga.edu> > > In compat_do_replace(), a temporary buffer is allocated through vmalloc() > to hold entries copied from the user space. The buffer address is firstly > saved to 'newinfo->entries', and later on assigned to 'entries_tmp'. Then > the entries in this temporary buffer is copied to the internal kernel > structure through compat_copy_entries(). If this copy process fails, > compat_do_replace() should be terminated. However, the allocated temporary > buffer is not freed on this path, leading to a memory leak. > > To fix the bug, free the buffer before returning from compat_do_replace(). > > Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu> > --- > net/bridge/netfilter/ebtables.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c > index 963dfdc..fd84b48e 100644 > --- a/net/bridge/netfilter/ebtables.c > +++ b/net/bridge/netfilter/ebtables.c > @@ -2261,8 +2261,10 @@ static int compat_do_replace(struct net *net, void __user *user, > state.buf_kern_len = size64; > > ret = compat_copy_entries(entries_tmp, tmp.entries_size, &state); > - if (WARN_ON(ret < 0)) > + if (WARN_ON(ret < 0)) { > + vfree(entries_tmp); > goto out_unlock; > + } Would it be worth adding a new goto label above out_unlock and free this entries_tmp? It could then be used in previous failure path as well. Thanks, Liam
On Mon, Jul 22, 2019 at 7:34 AM Liam R. Howlett <Liam.Howlett@oracle.com> wrote: > > Nice catch. The code that exists is confusing due to newinfo->entries > being overwritten and then freed in the existing code path as you state > in your commit log. > > * Wenwen Wang <wang6495@umn.edu> [190720 08:23]: > > From: Wenwen Wang <wenwen@cs.uga.edu> > > > > In compat_do_replace(), a temporary buffer is allocated through vmalloc() > > to hold entries copied from the user space. The buffer address is firstly > > saved to 'newinfo->entries', and later on assigned to 'entries_tmp'. Then > > the entries in this temporary buffer is copied to the internal kernel > > structure through compat_copy_entries(). If this copy process fails, > > compat_do_replace() should be terminated. However, the allocated temporary > > buffer is not freed on this path, leading to a memory leak. > > > > To fix the bug, free the buffer before returning from compat_do_replace(). > > > > Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu> > > --- > > net/bridge/netfilter/ebtables.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c > > index 963dfdc..fd84b48e 100644 > > --- a/net/bridge/netfilter/ebtables.c > > +++ b/net/bridge/netfilter/ebtables.c > > @@ -2261,8 +2261,10 @@ static int compat_do_replace(struct net *net, void __user *user, > > state.buf_kern_len = size64; > > > > ret = compat_copy_entries(entries_tmp, tmp.entries_size, &state); > > - if (WARN_ON(ret < 0)) > > + if (WARN_ON(ret < 0)) { > > + vfree(entries_tmp); > > goto out_unlock; > > + } > > > Would it be worth adding a new goto label above out_unlock and free this > entries_tmp? It could then be used in previous failure path as well. Yes, that would make the code much clearer and easier to understand. Thanks! Wenwen
diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c index 963dfdc..fd84b48e 100644 --- a/net/bridge/netfilter/ebtables.c +++ b/net/bridge/netfilter/ebtables.c @@ -2261,8 +2261,10 @@ static int compat_do_replace(struct net *net, void __user *user, state.buf_kern_len = size64; ret = compat_copy_entries(entries_tmp, tmp.entries_size, &state); - if (WARN_ON(ret < 0)) + if (WARN_ON(ret < 0)) { + vfree(entries_tmp); goto out_unlock; + } vfree(entries_tmp); tmp.entries_size = size64;