> On Wed, 2023-10-11 at 16:43 +0800, 黄思聪 wrote:
> > Pointer dereference error may occur in "alloc_init_deleg" function.
> >
> > The "alloc_init_deleg" function located in "fs/nfsd/nfs4state.c" may occur a pointer dereference error when it calls the function "nfs4_alloc_stid" located in the same kernel file. The "nfs4_alloc_stid" function will call the "kmem_cache_zalloc" function to allocate enough memory for storing the "stid" variable. If there are significant memory fragmentation issues, insufficient free memory blocks, or internal errors in the allocation function, the "kmem_cache_zalloc" function will return NULL. Then the "nfs4_alloc_stid" function will return NULL to the "alloc_init_deleg" function. Finally, the "alloc_init_deleg" function will execute the following instructions.
> > dp = delegstateid(nfs4_alloc_stid(clp, deleg_slab, nfs4_free_deleg));
> > if (dp == NULL)
> > goto out_dec;
> > dp->dl_stid.sc_stateid.si_generation = 1;
> >
> > The "delegstateid" function is defined as below:
> > static inline struct nfs4_delegation *delegstateid(struct nfs4_stid *s)
> > {
> > return container_of(s, struct nfs4_delegation, dl_stid);
> > }
> >
> > When the parameter "struct nfs4_stid *s" is NULL, the function will return a strange value which is a negative number. The value will be interpreted as a very large number. Then the variable "dp" in the "alloc_init_deleg" function will get the value, and it will pass the following "if" conditional statements. In the last, the variable "dp" will be dereferenced, and it will cause an error.
> >
> > My experimental kernel version is "LINUX 6.1", and this problem exists in all the version from "LINUX v3.2-rc1" to "LINUX v6.6-rc5".
>
>
> (I don't think there are security implications here, so I'm cc'ing the
> mailing list and making this public.)
>
> Well spotted! Ordinarily you'd be correct, but dl_stid is the first
> field in the struct, so the container_of will just return the same
> value that you pass in.
>
> Still, this is not something we ought to rely on going forward. Would
> you care to make a patch to clean this up and make that a bit less
> subtle?
>
> Thanks!
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
Thank you for your feedback! Indeed, you are correct! Next time I will check it twice before reporting a problem.
My patch is below:
Modify the conditional statement for null pointer check in the function
'alloc_init_deleg' to make this function more robust and clear. Otherwise,
this function may have potential pointer dereference problem in the future,
when modifying or expanding the nfs4_delegation structure.
Signed-off-by: Sicong Huang <huangsicong@xxxxxxxxx>
---
fs/nfsd/nfs4state.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index b1118050ff52..516b8bd6cb53 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1160,6 +1160,7 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
struct nfs4_clnt_odstate *odstate, u32 dl_type)
{
struct nfs4_delegation *dp;
+ struct nfs4_stid *stid;
long n;
dprintk("NFSD alloc_init_deleg\n");
@@ -1168,9 +1169,10 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
goto out_dec;
if (delegation_blocked(&fp->fi_fhandle))
goto out_dec;
- dp = delegstateid(nfs4_alloc_stid(clp, deleg_slab, nfs4_free_deleg));
- if (dp == NULL)
+ stid = nfs4_alloc_stid(clp, deleg_slab, nfs4_free_deleg);
+ if (stid == NULL)
goto out_dec;
+ dp = delegstateid(stid);
/*
* delegation seqid's are never incremented. The 4.1 special
--
2.34.1
Best Regards,
Sicong Huang
</huangsicong@xxxxxxxxx></jlayton@xxxxxxxxxx>
