lockd: preserve multiple NLM_SHARE grants from the same owner

When an NFSv3/NLM client issues multiple NLM_SHARE calls from a single
host for the same (file, owner) tuple, the current implementation
overwrites the recorded access and deny modes with the latest pair.
A subsequent NLM_UNSHARE then drops the entire entry, even if other
grants were implicitly subsumed by the most recent SHARE.  This is
particularly visible to Windows-style clients that map each open of
a file to a distinct NLM_SHARE, all carrying the same NLM owner
handle.  For example:

    1. SHARE(access=RW, deny=W)   -> entry [RW, deny W]
    2. SHARE(access=R,  deny=N)   -> entry [R, deny N]   (RW/W overwritten)
    3. UNSHARE(access=R, deny=N)  -> entry freed
    4. UNSHARE(access=RW, deny=W) -> nothing to release

NLM has no duplicate reply cache, so both SHARE and UNSHARE handlers
must be idempotent under UDP retransmit.

Track each (access, deny) pair with a single bit in a u16 bitmap.
fsh_access and fsh_mode are each in {0..3}, so there are 16 possible
pairs; index = (access << 2) | deny.  SHARE sets the bit, UNSHARE
clears it, both via idempotent bit operations.  s_access and s_mode
are recomputed as the union of the (access, deny) values whose bit
is set, and the entry is freed once s_access_deny_bmap reaches zero.

NLM_UNSHARE gains the access and deny modes as arguments so the
correct bit can be cleared.  The two callers in svcproc.c and
svc4proc.c are updated to forward the decoded values.

Signed-off-by: Oscar Ou <oscarou@synology.com>
Link: https://patch.msgid.link/20260703063856.2423734-1-oscarou@synology.com
Signed-off-by: Chuck Lever <cel@kernel.org>

fs/lockd/share.h

@@ -8,9 +8,14 @@
 #ifndef _LOCKD_SHARE_H
 #define _LOCKD_SHARE_H
 
+#include <linux/bits.h>
+
 /* Synthetic svid for lockowner lookup during share operations */
 #define LOCKD_SHARE_SVID	(~(u32)0)
 
+/* One bit per (access, deny) pair; index = (access << 2) | deny */
+#define LOCKD_FSH_BIT(a, d)	BIT(((a) << 2) | (d))
+
 /*
  * DOS share for a specific file
  */
@@ -21,12 +26,13 @@ struct lockd_share {
 	struct xdr_netobj	s_owner;	/* owner handle */
 	u32			s_access;	/* access mode */
 	u32			s_mode;		/* deny mode */
+	u16			s_access_deny_bmap;	/* held (access, deny) pairs */
 };
 
 __be32	nlmsvc_share_file(struct nlm_host *host, struct nlm_file *file,
 			  struct xdr_netobj *oh, u32 access, u32 mode);
 __be32	nlmsvc_unshare_file(struct nlm_host *host, struct nlm_file *file,
-			    struct xdr_netobj *oh);
+			    struct xdr_netobj *oh, u32 access, u32 mode);
 void	nlmsvc_traverse_shares(struct nlm_host *, struct nlm_file *,
 					       nlm_host_match_fn_t);
 

fs/lockd/svc4proc.c

@@ -1079,7 +1079,9 @@ static __be32 nlm4svc_proc_unshare(struct svc_rqst *rqstp)
 	if (resp->xdrgen.stat)
 		goto out;
 
-	resp->xdrgen.stat = nlmsvc_unshare_file(host, file, &lock->oh);
+	resp->xdrgen.stat = nlmsvc_unshare_file(host, file, &lock->oh,
+						argp->xdrgen.share.access,
+						argp->xdrgen.share.mode);
 
 	nlmsvc_release_lockowner(lock);
 

fs/lockd/svcproc.c

@@ -1098,7 +1098,9 @@ static __be32 nlmsvc_proc_unshare(struct svc_rqst *rqstp)
 	if (resp->xdrgen.stat)
 		goto out;
 
-	resp->xdrgen.stat = nlmsvc_unshare_file(host, file, &lock->oh);
+	resp->xdrgen.stat = nlmsvc_unshare_file(host, file, &lock->oh,
+						argp->xdrgen.share.access,
+						argp->xdrgen.share.mode);
 
 	nlmsvc_release_lockowner(lock);
 

fs/lockd/svcshare.c

@@ -25,6 +25,25 @@ nlm_cmp_owner(struct lockd_share *share, struct xdr_netobj *oh)
 	    && !memcmp(share->s_owner.data, oh->data, oh->len);
 }
 
+/*
+ * Recompute s_access / s_mode as the union of every (access, deny) pair
+ * whose bit is currently set in s_access_deny_bmap.
+ */
+static void nlm_recompute_share(struct lockd_share *share)
+{
+	u32 new_access = 0, new_mode = 0;
+	unsigned int i;
+
+	for (i = 0; i < 16; i++) {
+		if (share->s_access_deny_bmap & BIT(i)) {
+			new_access |= i >> 2;
+			new_mode   |= i & 3;
+		}
+	}
+	share->s_access = new_access;
+	share->s_mode = new_mode;
+}
+
 /**
  * nlmsvc_share_file - create a share
  * @host: Network client peer
@@ -64,12 +83,13 @@ nlmsvc_share_file(struct nlm_host *host, struct nlm_file *file,
 	share->s_host       = host;
 	share->s_owner.data = ohdata;
 	share->s_owner.len  = oh->len;
+	share->s_access_deny_bmap  = 0;
 	share->s_next       = file->f_shares;
 	file->f_shares      = share;
 
 update:
-	share->s_access = access;
-	share->s_mode = mode;
+	share->s_access_deny_bmap |= LOCKD_FSH_BIT(access, mode);
+	nlm_recompute_share(share);
 	return nlm_granted;
 }
 
@@ -78,12 +98,14 @@ nlmsvc_share_file(struct nlm_host *host, struct nlm_file *file,
  * @host: Network client peer
  * @file: File to be unshared
  * @oh: Share owner handle
+ * @access: Access mode of the SHARE being released
+ * @mode: Deny mode of the SHARE being released
  *
  * Returns an NLM status code.
  */
 __be32
 nlmsvc_unshare_file(struct nlm_host *host, struct nlm_file *file,
-		    struct xdr_netobj *oh)
+		    struct xdr_netobj *oh, u32 access, u32 mode)
 {
 	struct lockd_share	*share, **shpp;
 
@@ -93,8 +115,12 @@ nlmsvc_unshare_file(struct nlm_host *host, struct nlm_file *file,
 	for (shpp = &file->f_shares; (share = *shpp) != NULL;
 					shpp = &share->s_next) {
 		if (share->s_host == host && nlm_cmp_owner(share, oh)) {
-			*shpp = share->s_next;
-			kfree(share);
+			share->s_access_deny_bmap &= ~LOCKD_FSH_BIT(access, mode);
+			nlm_recompute_share(share);
+			if (!share->s_access_deny_bmap) {
+				*shpp = share->s_next;
+				kfree(share);
+			}
 			return nlm_granted;
 		}
 	}