[PATCH pstore fix v1] pstore: fix use after free

[PATCH pstore fix v1] pstore: fix use after free

[Norbert Manthey]

The pstore_mkfile() function is passed a pointer to a struct
pstore_record. On success it consumes this 'record' pointer and
references it from the created inode.

On failure, however, it may or may not free the record. There are even
two different code paths which return -ENOMEM -- one of which does and
the other doesn't free the record.

Make the behaviour deterministic by never consuming and freeing the
record when returning failure, allowing the caller to do the cleanup
consistently.

Signed-off-by: Norbert Manthey <nmanthey@amazon.de>

---
 fs/pstore/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -333,7 +333,6 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
 	private = kzalloc(sizeof(*private), GFP_KERNEL);
 	if (!private)
 		goto fail_alloc;
-	private->record = record;
 
 	switch (record->type) {
 	case PSTORE_TYPE_DMESG:
@@ -387,6 +386,8 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
 	if (!dentry)
 		goto fail_private;
 
+	private->record = record;
+
 	inode->i_size = private->total_size = size;
 
 	inode->i_private = private;
-- 
2.7.4




Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Ralf Herbrich
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879

Re: [PATCH pstore fix v1] pstore: fix use after free

[Kees Cook]

On Fri, Jul 05, 2019 at 03:06:00PM +0200, Norbert Manthey wrote:
> The pstore_mkfile() function is passed a pointer to a struct
> pstore_record. On success it consumes this 'record' pointer and
> references it from the created inode.
> 
> On failure, however, it may or may not free the record. There are even
> two different code paths which return -ENOMEM -- one of which does and
> the other doesn't free the record.
> 
> Make the behaviour deterministic by never consuming and freeing the
> record when returning failure, allowing the caller to do the cleanup
> consistently.

Yup, good catch. Looks like a double-free in the one failure case.

> Signed-off-by: Norbert Manthey <nmanthey@amazon.de>

Fixes: 83f70f0769ddd ("pstore: Do not duplicate record metadata")
Fixes: 1dfff7dd67d1a ("pstore: Pass record contents instead of copying")
Cc: stable@vger.kernel.org

Applied to my pstore tree. :)

-Kees

> ---
>  fs/pstore/inode.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
> --- a/fs/pstore/inode.c
> +++ b/fs/pstore/inode.c
> @@ -333,7 +333,6 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
>  	private = kzalloc(sizeof(*private), GFP_KERNEL);
>  	if (!private)
>  		goto fail_alloc;
> -	private->record = record;
>  
>  	switch (record->type) {
>  	case PSTORE_TYPE_DMESG:
> @@ -387,6 +386,8 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
>  	if (!dentry)
>  		goto fail_private;
>  
> +	private->record = record;
> +
>  	inode->i_size = private->total_size = size;
>  
>  	inode->i_private = private;
> -- 
> 2.7.4
> 
> 
> 
> 
> Amazon Development Center Germany GmbH
> Krausenstr. 38
> 10117 Berlin
> Geschaeftsfuehrung: Christian Schlaeger, Ralf Herbrich
> Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
> Sitz: Berlin
> Ust-ID: DE 289 237 879
> 
> 
> 

-- 
Kees Cook