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    Subject[PATCH AUTOSEL 4.14 099/103] kernfs: Fix range checks in kernfs_get_target_path
    Date
    From: Bernd Edlinger <bernd.edlinger@hotmail.de>

    [ 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>
    ---
    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 5145ae2f0572e..d273e3accade6 100644
    --- 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 */
    --
    2.20.1
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