| Message ID | 1508496110-2292-1-git-send-email-elena.reshetova@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Elena Reshetova <elena.reshetova@intel.com> writes: > atomic_t variables are currently used to implement reference > counters with the following properties: > - counter is initialized to 1 using atomic_set() > - a resource is freed upon counter reaching zero > - once counter reaches zero, its further > increments aren't allowed > - counter schema uses basic atomic operations > (set, inc, inc_not_zero, dec_and_test, etc.) > > Such atomic variables should be converted to a newly provided > refcount_t type and API that prevents accidental counter overflows > and underflows. This is important since overflows and underflows > can lead to use-after-free situation and be exploitable. > > The variable tcon_link.tl_count is used as pure reference counter. > Convert it to refcount_t and fix up the operations. <snip> > - cifs_get_tlink(tlink); > + refcount_set(&tlink->tl_count, 1); Since cifs_get_tlink() basically only increments the reference count and given that this is a new tlink I also think this replacement is ok. Looks good to me and passes 'make C=1'. Reviewed-by: Aurelien Aptel <aaptel@suse.com>
> Elena Reshetova <elena.reshetova@intel.com> writes: > > atomic_t variables are currently used to implement reference > > counters with the following properties: > > - counter is initialized to 1 using atomic_set() > > - a resource is freed upon counter reaching zero > > - once counter reaches zero, its further > > increments aren't allowed > > - counter schema uses basic atomic operations > > (set, inc, inc_not_zero, dec_and_test, etc.) > > > > Such atomic variables should be converted to a newly provided > > refcount_t type and API that prevents accidental counter overflows > > and underflows. This is important since overflows and underflows > > can lead to use-after-free situation and be exploitable. > > > > The variable tcon_link.tl_count is used as pure reference counter. > > Convert it to refcount_t and fix up the operations. > > <snip> > > > - cifs_get_tlink(tlink); > > + refcount_set(&tlink->tl_count, 1); > > Since cifs_get_tlink() basically only increments the reference count and > given that this is a new tlink I also think this replacement is ok. > > Looks good to me and passes 'make C=1'. > > Reviewed-by: Aurelien Aptel <aaptel@suse.com> Thank you very much for your review Aurelien! Do you know who would be the person to take this patch further? Best Regards, Elena. > > -- > Aurélien Aptel / SUSE Labs Samba Team > GPG: 1839 CB5F 9F5B FB9B AA97 8C99 03C8 A49B 521B D5D3 > SUSE Linux GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany > GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
merged into cifs-2.6.git for-next On Mon, Oct 30, 2017 at 10:03 AM, Aurélien Aptel <aaptel@suse.com> wrote: > Elena Reshetova <elena.reshetova@intel.com> writes: >> atomic_t variables are currently used to implement reference >> counters with the following properties: >> - counter is initialized to 1 using atomic_set() >> - a resource is freed upon counter reaching zero >> - once counter reaches zero, its further >> increments aren't allowed >> - counter schema uses basic atomic operations >> (set, inc, inc_not_zero, dec_and_test, etc.) >> >> Such atomic variables should be converted to a newly provided >> refcount_t type and API that prevents accidental counter overflows >> and underflows. This is important since overflows and underflows >> can lead to use-after-free situation and be exploitable. >> >> The variable tcon_link.tl_count is used as pure reference counter. >> Convert it to refcount_t and fix up the operations. > > <snip> > >> - cifs_get_tlink(tlink); >> + refcount_set(&tlink->tl_count, 1); > > Since cifs_get_tlink() basically only increments the reference count and > given that this is a new tlink I also think this replacement is ok. > > Looks good to me and passes 'make C=1'. > > Reviewed-by: Aurelien Aptel <aaptel@suse.com> > > -- > Aurélien Aptel / SUSE Labs Samba Team > GPG: 1839 CB5F 9F5B FB9B AA97 8C99 03C8 A49B 521B D5D3 > SUSE Linux GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany > GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) > -- > To unsubscribe from this list: send the line "unsubscribe linux-cifs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h index de5b2e1..18963bf 100644 --- a/fs/cifs/cifsglob.h +++ b/fs/cifs/cifsglob.h @@ -28,6 +28,7 @@ #include "cifsacl.h" #include <crypto/internal/hash.h> #include <linux/scatterlist.h> +#include <linux/refcount.h> #include <uapi/linux/cifs/cifs_mount.h> #include "smb2pdu.h" @@ -974,7 +975,7 @@ struct tcon_link { #define TCON_LINK_PENDING 1 #define TCON_LINK_IN_TREE 2 unsigned long tl_time; - atomic_t tl_count; + refcount_t tl_count; struct cifs_tcon *tl_tcon; }; @@ -992,7 +993,7 @@ static inline struct tcon_link * cifs_get_tlink(struct tcon_link *tlink) { if (tlink && !IS_ERR(tlink)) - atomic_inc(&tlink->tl_count); + refcount_inc(&tlink->tl_count); return tlink; } diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c index 0bfc228..f861152 100644 --- a/fs/cifs/connect.c +++ b/fs/cifs/connect.c @@ -2868,7 +2868,7 @@ cifs_put_tlink(struct tcon_link *tlink) if (!tlink || IS_ERR(tlink)) return; - if (!atomic_dec_and_test(&tlink->tl_count) || + if (!refcount_dec_and_test(&tlink->tl_count) || test_bit(TCON_LINK_IN_TREE, &tlink->tl_flags)) { tlink->tl_time = jiffies; return; @@ -4328,7 +4328,7 @@ cifs_sb_tlink(struct cifs_sb_info *cifs_sb) newtlink->tl_tcon = ERR_PTR(-EACCES); set_bit(TCON_LINK_PENDING, &newtlink->tl_flags); set_bit(TCON_LINK_IN_TREE, &newtlink->tl_flags); - cifs_get_tlink(newtlink); + refcount_set(&newtlink->tl_count, 1); spin_lock(&cifs_sb->tlink_tree_lock); /* was one inserted after previous search? */ @@ -4406,11 +4406,11 @@ cifs_prune_tlinks(struct work_struct *work) tlink = rb_entry(tmp, struct tcon_link, tl_rbnode); if (test_bit(TCON_LINK_MASTER, &tlink->tl_flags) || - atomic_read(&tlink->tl_count) != 0 || + refcount_read(&tlink->tl_count) != 0 || time_after(tlink->tl_time + TLINK_IDLE_EXPIRE, jiffies)) continue; - cifs_get_tlink(tlink); + refcount_set(&tlink->tl_count, 1); clear_bit(TCON_LINK_IN_TREE, &tlink->tl_flags); rb_erase(tmp, root);