Btrfs: avoid buffer overrun in btrfs_printk

The buffer read-overrun would be triggered by a printk format
starting with <N>, where N is a single digit.  NUL-terminate
after strncpy.  Use memcpy, not strncpy, since we know the
string we're copying fits in the destination buffer and
contains no NUL byte.

Signed-off-by: Jim Meyering <meyering@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 2cd32175753d..46b26650415f 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -188,7 +188,8 @@ void btrfs_printk(struct btrfs_fs_info *fs_info, const char *fmt, ...)
         va_start(args, fmt);
 
         if (fmt[0] == '<' && isdigit(fmt[1]) && fmt[2] == '>') {
-                strncpy(lvl, fmt, 3);
+                memcpy(lvl, fmt, 3);
+                lvl[3] = '\0';
                 fmt += 3;
                 type = logtypes[fmt[1] - '0'];
         } else