From a75e78f21f9ad4b810868c89dbbabcc3931591ca Mon Sep 17 00:00:00 2001

From: Bernd Edlinger <bernd.edlinger@hotmail.de>

Date: Sat, 7 Jul 2018 17:52:47 +0000

Subject: [PATCH] kernfs: Fix range checks in kernfs_get_target_path

Git-commit: a75e78f21f9ad4b810868c89dbbabcc3931591ca

Patch-mainline: v4.20-rc1

References: bsc#1051510

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>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 fs/kernfs/symlink.c | 5 ++++-

 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c

index 305b220af45d..162f43b80c84 100644

--- a/fs/kernfs/symlink.c

+++ b/fs/kernfs/symlink.c

@@ -72,6 +72,9 @@ 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;

@@ -88,7 +91,7 @@ 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 */

-- 

2.16.4