Re: [PATCH] afs: Fix memory leak in afs_put_sysnames()

[David Howells]

Markus Elfring  wrote:

> > sysnames should be freed after refcnt being decreased to zero in
> > afs_put_sysnames().
> 
> * I suggest to use the wording “reference counter”.

Can you use ASCII quotes please?  Not all fonts contain these quotes, and
occasionally they got copied into commit messages.

> * Where did you notice a “memory leak” here?

He said "sysnames should be freed after refcnt being decreased to zero in
afs_put_sysnames()".

> * Will the tag “Fixes” become relevant for the commit message?

It is the correct tag.

David

Re: [PATCH] afs: Fix memory leak in afs_put_sysnames()

[David Howells]

Zhihao Cheng  wrote:

> sysnames should be freed after refcnt being decreased to zero in
> afs_put_sysnames().

Good catch.

> Besides, it would be better set net->sysnames to 'NULL' after net->sysnames
> being released if afs_put_sysnames() aims on an afs_sysnames object.

Why?  We don't normally clear pointers when cleaning up a struct - and of the
two places this is relevant, in one we fail to set up a namespace and in the
other we're tearing down a namespace.  In neither case should the pointer be
accessed again.

> @@ -894,7 +894,7 @@ static struct dentry *afs_lookup_atsys(struct inode *dir, 
> struct dentry *dentry,
>*/
>   ret = NULL;
>  out_s:
> - afs_put_sysnames(subs);
> + afs_put_sysnames_and_null(net);

This is definitely wrong.  We obtained a ref 23 lines above and dropped the
lock:

read_lock(>sysnames_lock);
subs = net->sysnames;
refcount_inc(>usage);
read_unlock(>sysnames_lock);

We are dropping *that* ref, not the one in the struct.

Just adding the missing kfree() call into afs_put_sysnames() should suffice,
thanks.

David

Re: [PATCH] afs: Fix memory leak in afs_put_sysnames()

[Markus Elfring]

> sysnames should be freed after refcnt being decreased to zero in
> afs_put_sysnames().

* I suggest to use the wording “reference counter”.

* Where did you notice a “memory leak” here?


> Besides, it would be better set net->sysnames
> to 'NULL' after net->sysnames being released if afs_put_sysnames()
> aims on an afs_sysnames object.

* Would you like to consider an adjustment for this information?

* How do you think about to add an imperative wording?

* Will the tag “Fixes” become relevant for the commit message?

Regards,
Markus

[PATCH] afs: Fix memory leak in afs_put_sysnames()

[Zhihao Cheng]

sysnames should be freed after refcnt being decreased to zero in
afs_put_sysnames(). Besides, it would be better set net->sysnames
to 'NULL' after net->sysnames being released if afs_put_sysnames()
aims on an afs_sysnames object.

Signed-off-by: Zhihao Cheng 
Cc:  # v4.17+
Fixes: 6f8880d8e681557 ("afs: Implement @sys substitution handling")
---
 fs/afs/dir.c  |  2 +-
 fs/afs/internal.h |  2 ++
 fs/afs/main.c |  4 ++--
 fs/afs/proc.c | 25 -
 4 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index d1e1caa23c8b..cb9d8aa91048 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -894,7 +894,7 @@ static struct dentry *afs_lookup_atsys(struct inode *dir, 
struct dentry *dentry,
 */
ret = NULL;
 out_s:
-   afs_put_sysnames(subs);
+   afs_put_sysnames_and_null(net);
kfree(buf);
 out_p:
key_put(key);
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 80255513e230..615dd5f9ad6f 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -1093,12 +1093,14 @@ extern void __net_exit afs_proc_cleanup(struct afs_net 
*);
 extern int afs_proc_cell_setup(struct afs_cell *);
 extern void afs_proc_cell_remove(struct afs_cell *);
 extern void afs_put_sysnames(struct afs_sysnames *);
+extern void afs_put_sysnames_and_null(struct afs_net *);
 #else
 static inline int afs_proc_init(struct afs_net *net) { return 0; }
 static inline void afs_proc_cleanup(struct afs_net *net) {}
 static inline int afs_proc_cell_setup(struct afs_cell *cell) { return 0; }
 static inline void afs_proc_cell_remove(struct afs_cell *cell) {}
 static inline void afs_put_sysnames(struct afs_sysnames *sysnames) {}
+static inline void afs_put_sysnames_and_null(struct afs_net *net) {}
 #endif
 
 /*
diff --git a/fs/afs/main.c b/fs/afs/main.c
index c9c45d7078bd..6bf73fc65fb5 100644
--- a/fs/afs/main.c
+++ b/fs/afs/main.c
@@ -132,7 +132,7 @@ static int __net_init afs_net_init(struct net *net_ns)
net->live = false;
afs_proc_cleanup(net);
 error_proc:
-   afs_put_sysnames(net->sysnames);
+   afs_put_sysnames_and_null(net);
 error_sysnames:
net->live = false;
return ret;
@@ -150,7 +150,7 @@ static void __net_exit afs_net_exit(struct net *net_ns)
afs_purge_servers(net);
afs_close_socket(net);
afs_proc_cleanup(net);
-   afs_put_sysnames(net->sysnames);
+   afs_put_sysnames_and_null(net);
 }
 
 static struct pernet_operations afs_net_ops = {
diff --git a/fs/afs/proc.c b/fs/afs/proc.c
index 468e1713bce1..26e1e73281a6 100644
--- a/fs/afs/proc.c
+++ b/fs/afs/proc.c
@@ -554,15 +554,30 @@ static int afs_proc_sysname_write(struct file *file, char 
*buf, size_t size)
goto out;
 }
 
-void afs_put_sysnames(struct afs_sysnames *sysnames)
+static void afs_free_sysnames(struct afs_sysnames *sysnames)
 {
int i;
 
+   for (i = 0; i < sysnames->nr; i++)
+   if (sysnames->subs[i] != afs_init_sysname &&
+   sysnames->subs[i] != sysnames->blank)
+   kfree(sysnames->subs[i]);
+   kfree(sysnames);
+}
+
+void afs_put_sysnames(struct afs_sysnames *sysnames)
+{
+   if (sysnames && refcount_dec_and_test(>usage))
+   afs_free_sysnames(sysnames);
+}
+
+void afs_put_sysnames_and_null(struct afs_net *net)
+{
+   struct afs_sysnames *sysnames = net->sysnames;
+
if (sysnames && refcount_dec_and_test(>usage)) {
-   for (i = 0; i < sysnames->nr; i++)
-   if (sysnames->subs[i] != afs_init_sysname &&
-   sysnames->subs[i] != sysnames->blank)
-   kfree(sysnames->subs[i]);
+   afs_free_sysnames(sysnames);
+   net->sysnames = NULL;
}
 }
 
-- 
2.25.4