locks: only validate the lock vs. f_mode in F_SETLK codepaths

v2: replace missing break in switch statement (as pointed out by Dave
    Jones)

commit bce7560d4946 (locks: consolidate checks for compatible
filp->f_mode values in setlk handlers) introduced a regression in the
F_GETLK handler.

flock64_to_posix_lock is a shared codepath between F_GETLK and F_SETLK,
but the f_mode checks should only be applicable to the F_SETLK codepaths
according to POSIX.

Instead of just reverting the patch, add a new function to do this
checking and have the F_SETLK handlers call it.

Cc: Dave Jones <davej@redhat.com>
Reported-and-Tested-by: Reuben Farrelly <reuben@reub.net>
Signed-off-by: Jeff Layton <jlayton@poochiereds.net>

1 files changed, 24 insertions, 12 deletions

diff --git a/fs/locks.c b/fs/locks.c
index e663aeac579e..e390bd9ae068 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -389,18 +389,6 @@ static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
         fl->fl_ops = NULL;
         fl->fl_lmops = NULL;
 
-        /* Ensure that fl->fl_filp has compatible f_mode */
-        switch (l->l_type) {
-        case F_RDLCK:
-                if (!(filp->f_mode & FMODE_READ))
-                        return -EBADF;
-                break;
-        case F_WRLCK:
-                if (!(filp->f_mode & FMODE_WRITE))
-                        return -EBADF;
-                break;
-        }
-
         return assign_type(fl, l->l_type);
 }
 
@@ -2034,6 +2022,22 @@ static int do_lock_file_wait(struct file *filp, unsigned int cmd,
         return error;
 }
 
+/* Ensure that fl->fl_filp has compatible f_mode for F_SETLK calls */
+static int
+check_fmode_for_setlk(struct file_lock *fl)
+{
+        switch (fl->fl_type) {
+        case F_RDLCK:
+                if (!(fl->fl_file->f_mode & FMODE_READ))
+                        return -EBADF;
+                break;
+        case F_WRLCK:
+                if (!(fl->fl_file->f_mode & FMODE_WRITE))
+                        return -EBADF;
+        }
+        return 0;
+}
+
 /* Apply the lock described by l to an open file descriptor.
  * This implements both the F_SETLK and F_SETLKW commands of fcntl().
  */
@@ -2071,6 +2075,10 @@ again:
         if (error)
                 goto out;
 
+        error = check_fmode_for_setlk(file_lock);
+        if (error)
+                goto out;
+
         /*
          * If the cmd is requesting file-private locks, then set the
          * FL_OFDLCK flag and override the owner.
@@ -2206,6 +2214,10 @@ again:
         if (error)
                 goto out;
 
+        error = check_fmode_for_setlk(file_lock);
+        if (error)
+                goto out;
+
         /*
          * If the cmd is requesting file-private locks, then set the
          * FL_OFDLCK flag and override the owner.