From ed2849d3ecfa339435818eeff28f6c3424300cec Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Tue, 16 Nov 2010 16:55:19 +1100 Subject: [PATCH 1/2] sunrpc: prevent use-after-free on clearing XPT_BUSY When an xprt is created, it has a refcount of 1, and XPT_BUSY is set. The refcount is *not* owned by the thread that created the xprt (as is clear from the fact that creators never put the reference). Rather, it is owned by the absence of XPT_DEAD. Once XPT_DEAD is set, (And XPT_BUSY is clear) that initial reference is dropped and the xprt can be freed. So when a creator clears XPT_BUSY it is dropping its only reference and so must not touch the xprt again. However svc_recv, after calling ->xpo_accept (and so getting an XPT_BUSY reference on a new xprt), calls svc_xprt_recieved. This clears XPT_BUSY and then svc_xprt_enqueue - this last without owning a reference. This is dangerous and has been seen to leave svc_xprt_enqueue working with an xprt containing garbage. So we need to hold an extra counted reference over that call to svc_xprt_received. For safety, any time we clear XPT_BUSY and then use the xprt again, we first get a reference, and the put it again afterwards. Note that svc_close_all does not need this extra protection as there are no threads running, and the final free can only be called asynchronously from such a thread. Signed-off-by: NeilBrown Cc: stable@kernel.org Signed-off-by: J. Bruce Fields --- net/sunrpc/svc_xprt.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index ea2ff78dcf7b..3f2c5559ca1a 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -212,6 +212,7 @@ int svc_create_xprt(struct svc_serv *serv, const char *xprt_name, spin_lock(&svc_xprt_class_lock); list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) { struct svc_xprt *newxprt; + unsigned short newport; if (strcmp(xprt_name, xcl->xcl_name)) continue; @@ -230,8 +231,9 @@ int svc_create_xprt(struct svc_serv *serv, const char *xprt_name, spin_lock_bh(&serv->sv_lock); list_add(&newxprt->xpt_list, &serv->sv_permsocks); spin_unlock_bh(&serv->sv_lock); + newport = svc_xprt_local_port(newxprt); clear_bit(XPT_BUSY, &newxprt->xpt_flags); - return svc_xprt_local_port(newxprt); + return newport; } err: spin_unlock(&svc_xprt_class_lock); @@ -425,8 +427,13 @@ void svc_xprt_received(struct svc_xprt *xprt) { BUG_ON(!test_bit(XPT_BUSY, &xprt->xpt_flags)); xprt->xpt_pool = NULL; + /* As soon as we clear busy, the xprt could be closed and + * 'put', so we need a reference to call svc_xprt_enqueue with: + */ + svc_xprt_get(xprt); clear_bit(XPT_BUSY, &xprt->xpt_flags); svc_xprt_enqueue(xprt); + svc_xprt_put(xprt); } EXPORT_SYMBOL_GPL(svc_xprt_received); From c1ac3ffcd0bc7e9617f62be8c7043d53ab84deac Mon Sep 17 00:00:00 2001 From: Neil Brown Date: Thu, 2 Dec 2010 11:14:30 +1100 Subject: [PATCH 2/2] nfsd: Fix possible BUG_ON firing in set_change_info If vfs_getattr in fill_post_wcc returns an error, we don't set fh_post_change. For NFSv4, this can result in set_change_info triggering a BUG_ON. i.e. fh_post_saved being zero isn't really a bug. So: - instead of BUGging when fh_post_saved is zero, just clear ->atomic. - if vfs_getattr fails in fill_post_wcc, take a copy of i_ctime anyway. This will be used i seg_change_info, but not overly trusted. - While we are there, remove the pointless 'if' statements in set_change_info. There is no harm setting all the values. Signed-off-by: NeilBrown Cc: stable@kernel.org Signed-off-by: J. Bruce Fields --- fs/nfsd/nfs3xdr.c | 6 ++++-- fs/nfsd/xdr4.h | 21 ++++++++++----------- 2 files changed, 14 insertions(+), 13 deletions(-) diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c index 2a533a0af2a9..7e84a852cdae 100644 --- a/fs/nfsd/nfs3xdr.c +++ b/fs/nfsd/nfs3xdr.c @@ -260,9 +260,11 @@ void fill_post_wcc(struct svc_fh *fhp) err = vfs_getattr(fhp->fh_export->ex_path.mnt, fhp->fh_dentry, &fhp->fh_post_attr); fhp->fh_post_change = fhp->fh_dentry->d_inode->i_version; - if (err) + if (err) { fhp->fh_post_saved = 0; - else + /* Grab the ctime anyway - set_change_info might use it */ + fhp->fh_post_attr.ctime = fhp->fh_dentry->d_inode->i_ctime; + } else fhp->fh_post_saved = 1; } diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h index 4d476ff08ae6..60fce3dc5cb5 100644 --- a/fs/nfsd/xdr4.h +++ b/fs/nfsd/xdr4.h @@ -484,18 +484,17 @@ static inline bool nfsd4_not_cached(struct nfsd4_compoundres *resp) static inline void set_change_info(struct nfsd4_change_info *cinfo, struct svc_fh *fhp) { - BUG_ON(!fhp->fh_pre_saved || !fhp->fh_post_saved); - cinfo->atomic = 1; + BUG_ON(!fhp->fh_pre_saved); + cinfo->atomic = fhp->fh_post_saved; cinfo->change_supported = IS_I_VERSION(fhp->fh_dentry->d_inode); - if (cinfo->change_supported) { - cinfo->before_change = fhp->fh_pre_change; - cinfo->after_change = fhp->fh_post_change; - } else { - cinfo->before_ctime_sec = fhp->fh_pre_ctime.tv_sec; - cinfo->before_ctime_nsec = fhp->fh_pre_ctime.tv_nsec; - cinfo->after_ctime_sec = fhp->fh_post_attr.ctime.tv_sec; - cinfo->after_ctime_nsec = fhp->fh_post_attr.ctime.tv_nsec; - } + + cinfo->before_change = fhp->fh_pre_change; + cinfo->after_change = fhp->fh_post_change; + cinfo->before_ctime_sec = fhp->fh_pre_ctime.tv_sec; + cinfo->before_ctime_nsec = fhp->fh_pre_ctime.tv_nsec; + cinfo->after_ctime_sec = fhp->fh_post_attr.ctime.tv_sec; + cinfo->after_ctime_nsec = fhp->fh_post_attr.ctime.tv_nsec; + } int nfs4svc_encode_voidres(struct svc_rqst *, __be32 *, void *);