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    Subject[PATCH] kernfs: fix potential null-ptr-deref in kernfs_path_from_node_locked()
    Date
    Ensure that the 'buf' is not empty before strlcpy() uses it.

    Commit bbe70e4e4211 ("fs: kernfs: Fix possible null-pointer dereferences
    in kernfs_path_from_node_locked()") first noticed this, but it didn't
    fix it completely.

    Fixes: 9f6df573a404 ("kernfs: Add API to generate relative kernfs path")
    Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
    ---
    fs/kernfs/dir.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
    index f33b3baad07cb36..b2422265c86edf2 100644
    --- a/fs/kernfs/dir.c
    +++ b/fs/kernfs/dir.c
    @@ -140,6 +140,9 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
    size_t depth_from, depth_to, len = 0;
    int i, j;

    + if (!buf)
    + return -EINVAL;
    +
    if (!kn_to)
    return strlcpy(buf, "(null)", buflen);

    @@ -149,9 +152,6 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
    if (kn_from == kn_to)
    return strlcpy(buf, "/", buflen);

    - if (!buf)
    - return -EINVAL;
    -
    common = kernfs_common_ancestor(kn_from, kn_to);
    if (WARN_ON(!common))
    return -EINVAL;
    --
    2.25.1
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