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kernfs: Fix range checks in kernfs_get_target_path

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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>
This commit is contained in:
Bernd Edlinger 2018-07-07 17:52:47 +00:00 committed by Greg Kroah-Hartman
parent bdae566d5d
commit a75e78f21f
1 changed files with 4 additions and 1 deletions
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5
fs/kernfs/symlink.c
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@ -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 */