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cifs: fix possible uninitialized access and race on iface_list

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iface[0] was accessed regardless of the count value and without
locking.

* check count before accessing any ifaces
* make copy of iface list (it's a simple POD array) and use it without
  locking.

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
This commit is contained in:
Aurelien Aptel 2019-12-04 16:14:54 +01:00 committed by Steve French
parent 3345bb44ba
commit 9a7d5a9e6d
1 changed files with 26 additions and 3 deletions
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29
fs/cifs/sess.c
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@ -77,6 +77,8 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
int i = 0;
int rc = 0;
int tries = 0;
struct cifs_server_iface *ifaces = NULL;
size_t iface_count;
if (left <= 0) {
cifs_dbg(FYI,
@ -90,6 +92,26 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
return 0;
}
/*
* Make a copy of the iface list at the time and use that
* instead so as to not hold the iface spinlock for opening
* channels
*/
spin_lock(&ses->iface_lock);
iface_count = ses->iface_count;
if (iface_count <= 0) {
spin_unlock(&ses->iface_lock);
cifs_dbg(FYI, "no iface list available to open channels\n");
return 0;
}
ifaces = kmemdup(ses->iface_list, iface_count*sizeof(*ifaces),
GFP_ATOMIC);
if (!ifaces) {
spin_unlock(&ses->iface_lock);
return 0;
}
spin_unlock(&ses->iface_lock);
/*
* Keep connecting to same, fastest, iface for all channels as
* long as its RSS. Try next fastest one if not RSS or channel
@ -105,9 +127,9 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
break;
}
iface = &ses->iface_list[i];
iface = &ifaces[i];
if (is_ses_using_iface(ses, iface) && !iface->rss_capable) {
i = (i+1) % ses->iface_count;
i = (i+1) % iface_count;
continue;
}
@ -115,7 +137,7 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
if (rc) {
cifs_dbg(FYI, "failed to open extra channel on iface#%d rc=%d\n",
i, rc);
i = (i+1) % ses->iface_count;
i = (i+1) % iface_count;
continue;
}
@ -124,6 +146,7 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
left--;
}
kfree(ifaces);
return ses->chan_count - old_chan_count;
}