nfsd: more careful input validation in nfsctl write methods

Neil Brown points out that we're checking buf[size-1] in a couple places
without first checking whether size is zero.

Actually, given the implementation of simple_transaction_get(), buf[-1]
is zero, so in both of these cases the subsequent check of the value of
buf[size-1] will catch this case.

But it seems fragile to depend on that, so add explicit checks for this
case.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Acked-by: NeilBrown <neilb@suse.de>

1 files changed, 4 insertions, 1 deletions

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index bc22e0b0343a..8516137cdbb0 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -304,6 +304,9 @@ static ssize_t write_filehandle(struct file *file, char *buf, size_t size)
         struct auth_domain *dom;
         struct knfsd_fh fh;
 
+        if (size == 0)
+                return -EINVAL;
+
         if (buf[size-1] != '\n')
                 return -EINVAL;
         buf[size-1] = 0;
@@ -663,7 +666,7 @@ static ssize_t write_recoverydir(struct file *file, char *buf, size_t size)
         char *recdir;
         int len, status;
 
-        if (size > PATH_MAX || buf[size-1] != '\n')
+        if (size == 0 || size > PATH_MAX || buf[size-1] != '\n')
                 return -EINVAL;
         buf[size-1] = 0;