kernfs: Fix range checks in kernfs_get_target_path

[ Upstream commit a75e78f21f9ad4b810868c89dbbabcc3931591ca ]

The terminating NUL byte is only there because the buffer is
allocated with kzalloc(PAGE_SIZE, GFP_KERNEL), but since the
range-check is off-by-one, and PAGE_SIZE==PATH_MAX, the
returned string may not be zero-terminated if it is exactly
PATH_MAX characters long.  Furthermore also the initial loop
may theoretically exceed PATH_MAX and cause a fault.

Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c
index 5145ae2f0572e333d5ce6733a3c97881e9f28bab..d273e3accade642d47366f9176750da1bf1f79dc 100644 (file)
--- a/fs/kernfs/symlink.c
+++ b/fs/kernfs/symlink.c
@@ -63,6 +63,9 @@ static int kernfs_get_target_path(struct kernfs_node *parent,
                if (base == kn)
                        break;
 
+               if ((s - path) + 3 >= PATH_MAX)
+                       return -ENAMETOOLONG;
+
                strcpy(s, "../");
                s += 3;
                base = base->parent;
@@ -79,7 +82,7 @@ static int kernfs_get_target_path(struct kernfs_node *parent,
        if (len < 2)
                return -EINVAL;
        len--;
-       if ((s - path) + len > PATH_MAX)
+       if ((s - path) + len >= PATH_MAX)
                return -ENAMETOOLONG;
 
        /* reverse fillup of target string from target to base */